Solar Cell Vocabulary

superconductivity

The abrupt and large increase in electrical conductivity exhibited by some metals as the temperature approaches absolute zero.

Load

The amount of electric power used by any electrical unit or appliance at any given time.

power

The amount of electrical energy available for doing work, measured in horsepower, Watts, or Btu per hour.

Global Warming

The increase in the average temperature of the Earth's surface, atmosphere and oceans which is mainly linked to the increase of

Utility grid

The interconnection of electricity generation plants through the transmission and distribution lines to customers. The grid also refers to the interconnection of utilities through the electric transmission and distribution systems.

Vmp

Voltage at maximum power

Solar thermal

General term used to describe the use of the sun's energy as heat. Generally, no electricity is produced using solar thermal energy (but there are some systems that do). An example of this is a solar hot water system on the roof tops of many houses.

Distributed Power

Generic term for any power supply located near the point where the power is used. Opposite of central power.

Direct Bandgap

In a direct bandgap semiconductor, electrons at the conduction- band minimum can combine directly with holes at the valence band maximum, while conserving momentum

Electricity

Energy resulting from the flow of charged particles, such as electrons or ions.

Mounting Equipment

Equipment/apparatus used to fasten solar (PV) modules to the roof. Peak Load - The highest electrical demand within a particular period of time.

independent system operator (ISO)

The entity responsible for maintaining system balance, reliability, and electricity market operation.

Peak Sun Hours

The equivalent number of hours per day when solar irradiance averages 1,000 w/m2. For example, six peak sun hours means that the energy received during total daylight hours equals the energy that would have been received had the irradiance for six hours been 1,000 W/m2

discharge rate

The rate, usually expressed in amperes or time, at which electrical current is taken from the battery.

Duty Cycle:

The ratio of active time to total time that is used to describe the operating regime of appliances or loads in photovoltaic systems.

kerf

The width of a cut used to create wafers from silicon ingots, often resulting in the loss of semiconductor material.

load circuit

The wire, switches, fuses, etc. that connect the load to the power source.

Open-circuit Voltage

is the maximum voltage available from a solar cell, and this occurs at zero current.

maximum power point tracker

(MPPT)--A power conditioning unit that automatically operates the PV-generator at its maximum power point under all conditions. An MPPT will typically increase power delivered to the system by 10% to 40%, depending on climate conditions and battery state of charge. You usually get more gain in winter and in colder weather due to the higher panel output.Most MPPT controllers are down converters - from a higher voltage to a lower one.

MICROCRYSTALLINE SILICON

(also called nanocrystalline silicon) is amorphous silicon, but also contains small crystals; It absorbs a broader spectrum of light and is flexible.

HERMETIC SEAL

Being impervious to external influences. Typically associated with the sealing of a package so that oxygen, moisture, and other outside environments cannot enter the package

Photovoltaic

Capable of producing a voltage when exposed to radiant energy, especially light.

Texturing

Formation of pyramids in the surface of silicon to decrease the reflectivity of a surface

diffusion furnace

Furnace used to make junctions in semiconductors by diffusing dopant atoms into the surface of the material.

donor

In a photovoltaic device, an n-type dopant, such as phosphorus, that puts an additional electron into an energy level very near the conduction band; this electron is easily exited into the conduction band where it increases the electrical conductivity over than of an undoped semiconductor.

absorber

In a photovoltaic device, the material that readily absorbs photons to generate charge carriers (free electrons or holes).

Equilibrium

In p-n junction formation, this is the natural state where backward & forward current flows are equal. We see no net movement of charge once equilibrium is reached

Grain boundaries

Interfaces where crystals of different orientations meet.

voltage protection

Many inverters have sensing circuits that will disconnect the unit from the battery if input voltage limits are exceeded.

Conductor

Material which readily allows electric current to pass when a voltage is applied

Boost charge

Partial charge of a storage battery, usually at a high current rate for a short period.

tunneling

Quantum mechanical concept whereby an electron is found on the opposite side of an insulating barrier without having passed through or around the barrier.

Solar Thermal Electric Systems

Solar energy conversion technologies that convert solar energy to electricity, by heating a working fluid to power a turbine that drives a generator. Examples of these systems include central receiver systems, parabolic dish, and solar trough.

Customer load

The amount of power your site uses. Load may be expressed in kilowatts (capacity) or kilowatt-hours (energy). A site's peak kilowatts generally refers to when electric demand requirements are highest.

solar resource

The amount of solar insolation a site receives, usually measured in kWh/m2/day, which is equivalent to the number of peak sun hours.

current at maximum power (Imp)

The current at which maximum power is available from a module.

vacuum evaporation

The deposition of thin films of semiconductor material by the evaporation of elemental sources in a vacuum.

array current

The electrical current produced by a photovoltaic array when it is exposed to sunlight.

Enhanced greenhouse effect

The enhancement of Earth's natural greenhouse gases due to man made emissions of greenhouse gases, mostly carbon dioxide

projected area

The net south-facing glazing area projected on a vertical plane.

Power draw

The power drawn by a particular circuit element in a circuit

Lattice:

The regular periodic arrangement of atoms or molecules in a crystal of semiconductor material.

Contact Resistance

The resistance between metallic contacts and the semiconductor.

load resistance

The resistance presented by the load.

metrology

The science of measurement

Thermalisation

The situation where an electron has been given more energy by a photon than required to jump the energy bandgap, and subsequently the electron loses this surplus energy by 'bumping' into other nearby atoms (converting the kinetic energy to heat)

Solar Module

The smallest non divisible unit in a Solar PV Array (Also Solar PV Panel, Photovoltaic Module)

Hertz

The unit of electromagnetic frequency that is equal to one cycle per second.

low voltage disconnect

The voltage at which a charge controller will disconnect theload from the batteries to prevent over-discharging.

low voltage cutoff (LVC)

The voltage level at which a charge controller will disconnect the load from the battery.

ELECTROMAGNETIC SPECTRUM

a continuum of electric and magnetic radiation encompassing all wavelengths.

Instrinsic Carrier Concentration

concentration of free charge carriers formed by thermal excitation.

Sun path diagram

graphical representation of the Sun's height and azimuth.

turnkey power plant

in photovoltaics, a turnkey power plant is a fully configured solar power plant consisting of solar modules, assembly sys- tem, inverters and cabling.

conversion efficiency

(cell or module)--The ratio of the electric energy produced by a photovoltaic device (under one-sun conditions) to the energy from sunlight incident upon the cell.

passive solar home

--A house that uses a room or another part of the building as a solar collector, as opposed to active solar, such as PV.

Power Purchase Agreement (PPA)

A Power Purchase Agreement (PPA) is an agreement between a homeowner/building owner and

dry cell

A cell (battery) with a captive electrolyte. A primary battery that cannot be recharged

cadmium (Cd)

A chemical element used in making certain types of solar cells and batteries.

gallium (Ga)

A chemical element, metallic in nature, used in making certain kinds of solar cells and semiconductor devices.

Electrode:

A conductor that is brought in conducting contact with a ground.

Meter

A device that measures levels and volumes of customers' electricity and gas use.

Shunt

A device which allows electrical current to pass around another point in the circuit.

Ground fault

A difference in the currents in the hot and neutral wire which may cause electric shock

Module Derate Factor

A factor that lowers the photovoltaic module current to account for field operating conditions such as dirt accumulation on the module.

Solar Array

A group of solar panels collectively makes up a solar array.

III-V cell

A high-efficiency solar cell made from materials including Group III and Group V elements from the periodic table .

single-crystal material

A material that is composed of a single crystal or a few large crystals.

Platinum

A metal which is resistant to corrosion and is widely used for electrical contacts

chemical vapor deposition (CVD)

A method of depositing thin semiconductor films used to make certain types of photovoltaic devices. With this method, a substrate is exposed to one or more vaporized compounds, one or more of which contain desirable constituents. A chemical reaction is initiated, at or near the substrate surface, to produce the desired material that will condense on the substrate.

boule

A sausage-shaped, synthetic single-crystal mass grown in a special furnace, pulled and turned at a rate necessary to maintain the single-crystal structure during growth.

Metals

A shiny material that conducts heat and electricity very well. Flexible metals can be used as electricity conducting wires

dendrite

A slender threadlike spike of pure crystalline material, such as silicon.

microgroove

A small groove scribed into the surface of a solar cell, which is filled with metal for contacts.

On/Off Grid System

A solar energy system that is interconnected with the utility grid is said to be an on-grid or grid-tied system, while a system with battery storage is not interconnected and is described as an off-grid system.

Roof Mounted System

A solar system in which solar panels are mounted directly on the roof of a building or adjacent structure.

concentrating solar power (CSP)

A solar technology that use mirrors to reflect and concentrate sunlight onto receivers that convert solar energy to heat. This thermal energy is then used to produce electricity with a steam turbine or heat engine driving a generator.

Active solar heater

A solar water or space-heating system that moves heated air or water using pumps or fans.

Dielectric materials

A substance that is highly resistant to the flow of an electric current

Germanium

A type of semiconductor material. Has a smaller bandgap than other semiconducting materials

gigawatt (GW)

A unit of power equal to 1 billion Watts; 1 million kilowatts, or 1,000 megawatts

varistor

A voltage-dependent variable resistor. Normally used to protect sensitive equipment from power spikes or lightning strikes by shunting the energy to ground.

tin oxide

A wide band-gap semiconductor similar to indium oxide; used inheterojunction solar cells or to make a transparent conductive film, called NESA glass when deposited on glass.

CO2

An abbreviation for carbon dioxide. CO2 is well-known as a "green-house gas." When people talk about "Carbon Footprint," they are usually referring to CO2 emissions.

seasonal depth of discharge

An adjustment factor used in some system sizing procedures which "allows" the battery to be gradually discharged over a 30-90 day period of poor solar insolation. This factor results in a slightly smaller photovoltaic array.

hot spot

An undesirable phenomenon of PV device operation whereby one or more cells within a PV module or array act as a resistive load, resulting in local overheating or melting of the cell(s).

Intrinsic Semiconductor

An undoped semiconductor.

APCVD

Atmospheric pressure chemical vapor deposition.

c-Si - CRYSTALLINE SILICON SOLAR CELLS

(also called wafer silicon) are made of small silicon crystals. c-Si has been used as the light-absorbing semiconductor in most solar cells, even though it is a relatively poor absorber of light and requires a considerable thickness (several hundred microns) of material; it has proved convenient because it yields stable solar cells with good efficiencies (14-18%, half to three-quarters of the theoretical maximum -24%) and uses process technology developed from the huge knowledge base of the microelectronics industry. The silicon acts as both the source of photoelectrons, as well as providing the electric field to separate the charges and create a current. Two types of crystalline silicon are used in the industry: monocrystalline, produced by slicing wafers (up to 150mm diameter and 350 microns thick) from a high-purity single crystal boule; and polycrystalline silicon, made by sawing a cast block of silicon first into bars and then wafers (it is the main trend in crystalline silicon cell manufacture). At the sunward surface of the cell the highest possible average incident solar radiation is about 1000 W/m2.

PHOTOVOLTAIC WINDOW

(for buildings): a Building Integrated Photovoltaic (BIPV) module designed to act as a window and to simultaneously generate electricity through solar power. BIPV are photovoltaic modules integrated into the building fagade, substituting standard glass (windows) with glass laminates that encapsulate photovoltaic cells. BIPV panels (or modules) are incorporated into the building construction materials as an integrated unit; the photovoltaic system is designed for producing electricity and taking on the role of building element.

PHOTOTHERMAL TECHNOLOGY

(photothermic): the production of heat by photoexcitation (light); the photoexcitation of materials resulting in the production of thermal energy (heat). The sunlight is used to heat water or another fluid such as oil or antifreeze (sometimes to produce steam with which to drive a generator).

Gallium Arsenide (GaAs)

- A compound of the elements gallium and arsenic. A highly efficient crystalline semiconductor used in Solar PV modules . A crystalline, high-efficiency compound used to make certain types of solar cells and semiconductor material.

Orientation

- Placement with respect to the cardinal directions, North, South, East and West. Azimuth is the measure of orientation from the North

Czochralski Process

- a method of growing high quality semiconductor crystal by slowly lifting a seed crystal from a molten bath of the material under careful cooling conditions. Method was invented by polish engineer Jan Czohralski.

P-type Semiconductors

- are extrinsic semiconductors with a larger hole concentration than electron concentration.

Doping

- intentionally introducing impurities into an extremely pure (also referred to as intrinsic) semiconductor for the purpose of modulating its electrical properties.

Diffusion

- is the net movement of a substance (e.g., an atom, ion or molecule) from a region of high concentration to a region of low concentration

Fill Factor (FF)

- the ratio of the maximum power to the product of the open-circuit voltage and the short-circuit current (for an I-V curve, ) .2 The ratio of a photovoltaic cell's actual power to its power if both current andvoltage were at their maxima. A key characteristic in evaluating cell performance.

Building Integrated Photovoltaics (BIPV)

...

infrared radiation

...

Conduction Band (or conduction level):

1 an energy band in a semiconductor in which electrons can move freely in a solid, producing a net transport of charge. 2 The energy level required by an electron (or hole) for it to be considered free to escape its atom's valence shell and thus, conduct current.

Energy Audit

: A survey that shows how much energy used in a home and helps identify ways to use less energy.

Voltage regulator

: An electrical device used to keep voltage at predetermined levels.

Thermal Unit:

: One kWh = 3400 BTU. Can be compared to 860 calories (food value)

OPTOELECTRONICS

: technology concerned with the combined use of electronics and light; the study and application of electronic devices that source, detect and control light. It is usually considered a sub-field of photonics. Light often includes invisible forms of radiation such as gamma rays, X-rays, ultraviolet and infrared, in addition to visible light. Optoelectronics is based on the quantum mechanical effects of light on semiconducting materials, sometimes in the presence of electric fields.

grid-connected (PV system)

A PV system in which the PV array acts like a central generating plant, supplying power to the grid. A photovoltaic system that is connected to the electricity grid network via an inverter. 2 Because PV outputs DC electricity and grids are AC, this type of system must have an inverter between the PV and the grid to convert and feed AC power into the grid

Autonomous system

A PV system that operates without any other energy generating source. A stand-alone PV system that has no back-up generating source. May or may not include storage batteries. Most battery systems are designed for a certain minimum "days of autonomy" - which means that the batteries can supply sufficient power with no sunlight to charge the batteries. This varies from 3-5 days in the sunbelt, to 5 to 10 days elsewhere.

Solar Cell

A Solar PV cell (also called photovoltaic cell) is a solid state device that converts the energy of sunlight directly into electricity by the photovoltaic effect

Thin Film Solar PV

A Solar PV cell that is made by depositing one or more thin layers (thin film) of Solar PV material on a substrate. The thickness range of such a layer is wide and varies from a few nanometres to tens of micrometers

N-Type Silicon

A Solar PV silicon material that has been doped with a material that has more electrons in its atomic structure than does silicon. The most common example is silicon doped with phosphorous

Grid Connected System

A Solar PV system in which the array acts like a central generating plant, supplying power to the electricity grid.

Stand alone system

A Solar PV system that operates independently of the utility grid These are systems that are self-sufficient. They consist of a photovoltaic array, control circuits and batteries so that power can be supplied at any time (even at night - from the batteries). There is no connection to the grid. An example might be a calculator or a house that has not got a connection to the electrical grid

liquid electrolyte battery

A battery containing a liquid solution of acid and water. Distilled water may be added to these batteries to replenish the electrolyte as necessary. Also called a flooded battery because the plates are covered with the electrolyte

starved electrolyte cell

A battery containing little or no free fluid electrolyte.

nickel cadmium battery

A battery containing nickel and cadmium plates and an alkaline electrolyte.

vented cell

A battery designed with a vent mechanism to expel gases generated during charging.

captive electrolyte battery

A battery having an immobilized electrolyte (gelled or absorbed in a material).

float service

A battery operation in which the battery is normally connected to an external current source; for instance, a battery charger which supplies the battery load< under normal conditions, while also providing enough energy input to the battery to make up for its internal quiescent losses, thus keeping the battery always up to full power and ready for service

secondary battery

A battery that can be recharged

primary battery

A battery whose initial capacity cannot be restored by charging.

Sealed Battery

A battery with a captive electrolyte and a resealing vent cap, also called a valve‐regulated battery. Electrolyte cannot be added.

Deep‐Cycle Battery

A battery with large plates that can withstand many discharges to a low state‐of‐charge.

Shallow‐Cycle Battery

A battery with small plates that cannot withstand many discharges to a low state‐of‐charge.

Covalent Bond

A bond between atoms where each contribute one electron to the bond, so each atom can be considered as having both the electrons as part of its total collection. There are usually 2 electrons in each covalent bond for silicon.

ingot

A casting of material, usually crystalline silicon, from which slices or wafers can be cut for use in a solar cell.2 Molten and subsequently solidified silicon cubes or cylinders, ready for cutting into wafers

Schottky barrier

A cell barrier established as the interface between a semiconductor, such as silicon, and a sheet of metal.

trickle charge

A charge at a low rate, balancing through self-discharge losses, to maintain a cell or battery in a fully charged condition.

Series Controller

A charge controller that interrupts the charging current by open‐circuiting the photovoltaic (PV) array. The control element is in series with the PV array and battery.

single-stage controller

A charge controller that redirects all charging current as the battery nears full state-of-charge.

shunt controller

A charge controller that redirects or shunts the charging current away from the battery. The controller requires a large heat sink to dissipate the current from the short-circuited photovoltaic array. Most shunt controllers are for smaller systems producing 30 amperes or less.

Multi‐Stage Controller

A charging controller unit that allows different charging currents as the battery nears full state‐of‐charge.

dangling bonds

A chemical bond associated with an atom on the surface layer of a crystal. The bond does not join with another atom of the crystal, but extends in the direction of exterior of the surface.

dopant

A chemical element (impurity) added in small amounts to an otherwise pure semiconductor material to modify the electrical properties of the material. An n-dopant introduces more electrons. A p-dopant creates electron vacancies (holes).

Phosphorous (P):

A chemical element used as a dopant in making n‐type semiconductor layers.

Anisotropic etch

A chemical that etches (burns) away the surface of a semiconductor at different rates depending on the direction/plane. This way, by pouring the etching chemical on a material, some sides will burn off faster, leaving a particular shape (e.g. a pyramid)

temperature compensation

A circuit that adjusts the charge controller activation points depending on battery temperature. This feature is recommended if the battery temperature is expected to vary more than ±5°C from ambient temperature.

photovoltaic (PV) system

A complete set of components for converting sunlight into electricity by the photovoltaic process, including the array and balance of system components. 2 An installation of Solar PV modules and other components designed to produce power from sunlight and meet the power demand for a designated load.

vertical multijunction (VMJ) cell

A compound cell made of different semiconductormaterials in layers, one above the other. Sunlight entering the top passes through successive cell barriers, each of which converts a separate portion of the spectrum into electricity, thus achieving greater total conversion efficiency of the incident light. Also called a multiple junction cell. See also multijunction device and split-spectrum cell

split-spectrum cell

A compound photovoltaic device in which sunlight is first divided into spectral regions by optical means. Each region is then directed to a different photovoltaic cell optimized for converting that portion of the spectrum into electricity. Such a device achieves significantly greater overall conversion of incident sunlight into electricity. See alsomulitjunction device.

Electric field

A conceptual region where electrical charges experience a force due to other electrical charges nearby. The field is shown in lines, where closely-spaced lines indicate stronger forces experienced. The arrows on the lines indicate the direction a positive charge would flow if placed in that location in the field.

sulfation

A condition that afflicts unused and discharged batteries; large crystals of lead sulfate grow on the plate, instead of the usual tiny crystals, making the battery extremely difficult to recharge

stratification

A condition that occurs when the acid concentration varies from top to bottom in the battery electrolyte. Periodic, controlled charging at voltages that produce gassing will mix the electrolyte. See also equalization.

Partial shading

A condition where light to part of solar module or cell is blocked by external features such as tree or building

Crystal

A crystal is a solid with molecular building blocks, such as atoms or ions, that have arranged themselves in an identically repeating pattern along all three spatial dimensions

minority carrier

A current carrier, either an electron or a hole, that is in the minority in a specific layer of a semiconductor material; the diffusion of minority carriers under the action of the cell junction voltage is the current in a photovoltaic device.

storage battery

A device capable of transforming energy from electric to chemical form and vice versa. The reactions are almost completely reversible. During discharge, chemical energy is converted to electric energy and is consumed in an external circuit or apparatus.

electrochemical cell

A device containing two conducting electrodes, one positive and the other negative, made of dissimilar materials (usually metals) that are immersed in a chemical solution (electrolyte) that transmits positive ions from the negative to the positive electrode and thus forms an electrical charge. One or more cells constitute a battery.

photoelectric cell

A device for measuring light intensity that works by converting light falling on, or reach it, to electricity, and then measuring the current; used in photometers.

Alternator

A device for producing Alternating Current (AC) electricity. Usually driven by a motor, but can also be driven by other means, including water and wind power.

rectifier

A device that converts ac to dc, as in a battery charger or converter. See inverter and diode.

fuel cell

A device that converts the energy of a fuel directly to electricity and heat, without combustion. Because there is no combustion, fuel cells give off few emissions; because there are no moving parts, fuel cells are quiet.

Utility Meter

A device that measures the flow of electricity between a site that uses electricity and the electric utility company. When your solar system produces excess power, your meter literally spins backward.

Transformer

A device that transfers electrical energy from one circuit to another by magnetic coupling without requiring relative motion between its parts. It usually comprises two or more coupled windings, and, in most cases, a core to concentrate magnetic flux.

Ammeter

A device used for measuring current flow at any point in an electrical circuit.

Converter

A device used in Solar PV systems to convert electrical direct current (DC) voltage to another DC voltage

Anemometer

A device used to measure wind speed.

Thermophotovoltaic Cell (TPV):

A device where sunlight concentrated onto a absorber heats it to a high temperature, and the thermal radiation emitted by the absorber is used as the energy source for a photovoltaic cell that is designed to maximize conversion efficiency at the wavelength of the thermal radiation.

Blocking Diode

A diode used to restrict or block reverse current from flowing backward through a module. Alternatively, diode connected in series to a PV string; it protects its modules from a reverse power flow and, thus, against the risk of thermal destruction of solar cells.

transparent conducting oxide (TCO)

A doped metal oxide used to coat and improve the performance of optoelectronic devices such as photovoltaics and flat panel displays. Most TCO films are fabricated with polycrystalline or amorphous microstructures and are deposited on glass. The current industry-standard TCO is indium tin oxide. Indium is relatively rare and expensive, so research is ongoing to develop improved TCOs based on alternative materials.

Adjustable set point

A feature allowing the user to adjust the voltage levels at which acharge controller will become active.

measurement and characterization

A field of research that involves assessing the characteristics of photovoltaic materials and devices.

Charge Carrier

A free and mobile conduction electron or hole in a semiconductor

Greenhouse Gases

A gas that contributes to the greenhouse effect by absorbing infrared radiation. The most prevalent of these gases is carbon dioxide, which is released in large quantities when fossil fuels are burned. Nothing is burned to convert sunlight into power. Since solar energy does not have any gaseous by-products, it is considered "clean."

lead-acid battery

A general category that includes batteries with plates made of pure lead, lead-antimony, or lead-calcium immersed in an acid electrolyte.

I-V curve

A graphical presentation of the current versus the voltage from a photovoltaic device as the load is increased from the short circuit (no load) condition to the open circuit (maximum voltage) condition. The shape of the curve characterizes cell performance.

Photovoltaic array

A group of solar electric panels connected together.

Battery bank

A grouping of individual batteries such that they are electrically connected in series/parallel combinations to give the desired total output voltage and current. This group will have two outlet terminals with which to connect to a circuit, providing a single connection point to access all the batteries

Point‐Contact Cell

A high efficiency silicon photovoltaic concentrator cell that employs light trapping techniques and point‐diffused contacts on the rear surface for current collection.

multijunction device

A high-efficiency photovoltaic device containing two or more celljunctions, each of which is optimized for a particular part of the solar spectrum. A photovoltaic device containing two or more cell junctions, each of which is optimized for a particular part of the solar spectrum, to achieve greater overall efficiency.

thin film

A layer of semiconductor material, such as copper indium diselenide orgallium arsenide, a few microns or less in thickness, used to make photovoltaic cells. Commonly called amorphous. in the manufacturing of thin-film modules, active photo- voltaic layers are applied directly to a glass or metal pane in an integrated process. the thickness of the layer applied in this process is a mere 0.002 millimetres. the thin coating of the active substance, amorphous silicon (a-si), copper in- dium (gallium) diselenide (Cis/CiGs) or cadmium telluride (Cdte) for instance, reduces the amount of material used and the manufacturing costs. although, in comparison to crystalline modules, thin-film modules have lower conver- sion efficiencies, they have better temperature coefficients, are able to convert diffused light better and are less sensitive to shadowing.

intrinsic layer

A layer of semiconductor material, used in a photovoltaic device, whose properties are essentially those of the pure, undoped, material.

Compound

A material that combines multiple elements from the periodic table together in a single structure. Each element is chemically altered in this state, so the whole material exhibits different properties to a simple physical mixture of each element.

Semiconductor

A material that has properties somewhere between insulators and conductors. They can provide insulation at low energy levels (very low temperature and no sunlight) and conduct at higher energy levels (ambient temperatures and sunlight present). Doping of these materials changes their conductive properties and makes photovoltaics possible. Any material that has a limited capacity for conducting an electric current. Certain semiconductors, including silicon, gallium arsenide, copper indium diselenide, and cadmium telluride, are uniquely suited to the photovoltaic conversion process.

Polycrystalline Silicon

A material used to make Solar PV cells which are made from large blocks of molten silicon carefully cooled and solidified. (Also Multicrystalline silicon)

VOLTAGE

A measure of the force or "push" given the electrons in an electrical circuit; a measure of electrical potential. One volt produces one amp of current when acting against a resistance of one ohm. The amount of electromotive force, measured in volts, that exists between two points.

Plates:

A metal plate, usually lead or lead compound, immersed in the electrolyte in a battery.

balancing area

A metered segment of the power system, maintained by a balancing area authority, that ensures the total of all electrical generation equals the total of all system loads.

edge-defined film-fed growth (EFG)

A method for making sheets of polycrystalline silicon for photovoltaic devices in which molten silicon is drawn upward by capillary action through a mold.

dendritic web technique

A method for making sheets of polycrystalline silicon in which silicon dendrites are slowly withdrawn from a melt of silicon whereupon a web of silicon forms between the dendrites and solidifies as it rises from the melt and cools.

physical vapor deposition

A method of depositing thin semiconductor photovoltaic films. With this method, physical processes, such as thermal evaporation or bombardment of ions, are used to deposit elemental semiconductor material on a substrate.

Screen-printing

A method of forming metal grid lines on the top surface of a solar cell. This method uses a paste containing the metal and squeezes it through a stencil outline that only allows the metal to be laid in the required pattern on the cell.

Integrated circuit

A miniaturized electronic circuit (consisting mainly of semiconductor devices, as well as passive components) that has been manufactured in the surface of a thin substrate of semiconductor material.

ELECTRONS

A negatively charged particle. The movement of electrons in an electrical conductor constitutes an electric current.

String

A number of modules or panels interconnected electrically in series to produce the operating voltage required by the load. a string is the parallel wiring of a number of solar modules connected up electrically in a series.

charge factor

A number representing the time in hours during which a battery can be charged at a constant current without damage to the battery. Usually expressed in relation to the total battery capacity, i.e., C/5 indicates a charge factor of 5 hours. Related to charge rate

Photon

A photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. Solar radiation arrives on the surface of photovoltaic cells in the form of photons, providing the main energy that activates cells to produce electricity.

Flat‐Plate Array

A photovoltaic (PV) array that consists of non‐concentrating PV modules.

tracking array

A photovoltaic (PV) array that follows the path of the sun to maximize the solar radiation incident on the PV surface. The two most common orientations are (1) one axis where the array tracks the sun east to west and (2) two-axis tracking where the array points directly at the sun at all times. Tracking arrays use both the direct and diffuse sunlight. Two-axis tracking arrays capture the maximum possible daily energy.

Fixed Tilt Array

A photovoltaic array set in at a fixed angle with respect to horizontal.

inverted metamorphic multijunction (IMM) cell

A photovoltaic cell that is a multijunction device whose layers of semiconductors are grown upside down. This special manufacturing process yields an ultra-light and flexible cell that also converts solar energy with high efficiency.

combined collector

A photovoltaic device or module that provides useful heat energy in addition to electricity.

thin film photovoltaic module

A photovoltaic module constructed with sequential layers of thin film semiconductor materials. See also amorphous silicon.

Concentrator:

A photovoltaic module, which includes optical components such as lenses (Fresnel lens) to direct and concentrate sunlight onto a solar cell of smaller area. Most concentrator arrays must directly face or track the sun. They can increase the power flux of sunlight hundreds of times. 2 -- Concentrating arrays must track the sun and use only the direct sunlight because the diffuse portion cannot be focused onto the PV cells. Efficiency is increased, but lifespan is usually decreased due to the high heat.

photovoltaic-thermal (PV/T) system

A photovoltaic system that, in addition to converting sunlight into electricity, collects the residual heat energy and delivers both heat and electricity in usable form. Also called a total energy system or solar thermal system.

sacrificial anode

A piece of metal buried near a structure that is to be protected from corrosion. The metal of the sacrificial anode is intended to corrode and reduce the corrosion of the protected structure.

Pocket Plate

A plate for a battery in which active materials are held in a perforated metal pocket

copper zinc tin sulfide/selenide (CZTS)

A polycrystalline thin-film photovoltaic material

copper indium diselenide (CuInSe2, or CIS)

A polycrystalline thin-film photovoltaic material (sometimes incorporating gallium (CIGS) and/or sulfur).

Cadmium Telluride (CdTe)

A polycrystalline thin-film photovoltaic material. 2- A thin film Solar PV technology used in the production of Solar PV modules

Distributed Generation:

A popular term for localized or on‐site power generation.

qualification test

A procedure applied to a selected set of photovoltaic modules involving the application of defined electrical, mechanical, or thermal stress in a prescribed manner and amount. Test results are subject to a list of defined requirements.

cleavage of lateral epitaxial films for transfer (CLEFT)

A process for making inexpensive gallium arsenide (GaAs) photovoltaic cells in which a thin film of GaAs is grown atop a thick, single-crystal GaAs (or other suitable material) substrate and then is cleaved from the substrate and incorporated into a cell, allowing the substrate to be reused to grow more thin-film GaAs.

Sputtering:

A process used to apply photovoltaic semiconductor material to a substrate by a physical vapor deposition process where high‐energy ions are used to bombard elemental sources of semiconductor material, which eject vapors of atoms that are then deposited in thin layers on a substrate.

exciton

A quasi-particle created in a semiconductor that is composed of an electron hole pair in a bound state. An exciton can be generated by and converted back into a photon.

nominal voltage

A reference voltage used to describe batteries, modules, or systems (i.e., a 12-volt or 24-volt battery, module, or system).

heterojunction

A region of electrical contact between two different materials.

junction

A region of transition between semiconductor layers, such as a p/n junction, which goes from a region that has a high concentration of acceptors (p-type) to one that has a high concentration of donors (n-type).

Maintenance-Free Battery

A sealed battery to which water cannot be added to maintain electrolyte level.

junction diode

A semiconductor device with a junction and a built-in potential that passes current better in one direction than the other. All solar cells are junction diodes.

p-type semiconductor

A semiconductor in which holes carry the current; produced bydoping an intrinsic semiconductor with an electron acceptor impurity (e.g., boron insilicon). A semiconductor in which holes carry the current; produced by doping an intrinsic semiconductor with an electron acceptor impurity (e.g., boron in silicon).

P-I-N

A semiconductor photovoltaic (PV) device structure that layers an intrinsic semiconductor between a p-type semiconductor and an n-type semiconductor; this structure is most often used with amorphous silicon PV devices.

P/N

A semiconductor photovoltaic device structure in which the junction is formed between a p-type layer and an n-type layer.

n-type semiconductor

A semiconductor produced by doping an intrinsic semiconductor with an electron-donor impurity (e.g., phosphorous in silicon).

Ground Mounted Systems

A solar system that is not attached directly to a building, but is supported by a structure that is built low to the ground. Ground mounts are ideal for sites with limited roof space and a lot of open land.

Crystals

A solid in which the constituent atoms, molecules, or ions are packed in a regularly and strictly ordered repeating pattern extending in all three spatial dimensions. The material is quite rigid and the structure is usually highly stable

photovoltaic (PV) device

A solid-state electrical device that converts light directly intodirect current electricity of voltage-current characteristics that are a function of the characteristics of the light source and the materials in and design of the device. Solar photovoltaic devices are made of various semiconductor materials including silicon,cadmium sulfide, cadmium telluride, and gallium arsenide, and in single crystalline,multicrystalline, or amorphous forms.

one-axis tracking

A system capable of rotating about one axis, usually following the sun from East to West.

two-axis tracking

A system capable of rotating independently about two axes (e.g., vertical and horizontal) and following the sun for maximum efficiency of the solar array.

Reverse saturation current

A system that provides electricity in remote locations, without requiring connection to an electricity distribution system. Small leakage current that flows when a diode (or p-n junction) is operated in reverse bias or reverse polarity

Rankine cycle

A thermodynamic cycle used in steam turbines to convert heat energy into work. Concentrating solar power plants often rely on the Rankine cycle. In CSP systems, mirrors focus sunlight on a heat-transfer fluid. This is used to creates steam, which spins a turbine to generate electricity. rate is commonly normalized by a charge control device with respect to the rated capacity of the cell or battery.

polycrystalline thin film

A thin film made of multicrystalline material.

Ribbon silicon

A type of crystalline silicon which is fabricated by a variety of solidification (crystallization) methods that withdraw thin silicon sheets from pools of relatively pure molten silicon

Multicrystalline silicon

A type of crystalline silicon which typically has a simpler technique for production, and hence, is cheaper. The silicon is made up of many smaller crystals, all at different orientations

Crystalline Silicon:

A type of photovoltaic cell made from a slice of single‐crystal silicon or polycrystalline silicon.

Photoelectrochemical Cell:

A type of photovoltaic device in which the electricity induced in the cell is used immediately within the cell to produce a chemical, such as hydrogen, which can then be withdrawn for use.

ribbon (photovoltaic) cells

A type of photovoltaic device made in a continuous process of pulling material from a molten bath of photovoltaic material, such as silicon, to form a thin sheet of material.

internal quantum efficiency (internal QE or IQE)

A type of quantum efficiency. Refers to the efficiency with which light not transmitted through or reflected away from the cell can generate charge carriers that can generate current.

Transistor

A type of semiconductor device, commonly used as an amplifier. It is used widely in a variety of digital and analog functions, including amplification, switching, voltage regulation, signal modulation, and oscillators.

Harmonics

A wave of signal can be transmitted with waves of multiple frequencies overlayed on the main one. These are the harmonics and their allowable frequencies are always an integer multiple of the fundamental frequency

Sine Wave

A waveform corresponding to a single‐frequency periodic oscillation that can be mathematically represented as a function of amplitude versus angle in which the value of the curve at any point is equal to the sine of that angle.

modified sine wave

A waveform that has at least three states (i.e., positive, off, and negative). Has less harmonic content than a square wave.

series connection

A way of joining photovoltaic cells or batteries by connecting positive leads to negative leads; such a configuration increases the voltage.

parallel connection

A way of joining solar cells or photovoltaic modules by connecting positive leads together and negative leads together; such a configuration increases the current, but not the voltage. A wiring configuration used to increase current (amperage). Parallel wiring is positive to positive (+ to +) and negative to negative (- to -). Opposite of a series connection.

Window

A wide band gap material chosen for its transparency to light. Generally used as the top layer of a photovoltaic device, the window allows almost all of the light to reach the semiconductor layers beneath.

Indium Oxide

A wide band gap semiconductor that can be heavily doped with tin to make a highly conductive, transparent thin film. Often used as a front contact or one component of a heterojunction solar cell.

AGM

Absorbed Glass Mat, a newer type of battery construction that uses saturated absorbent glass mats rather than gelled or liquid electrolyte. Somewhat more expensive than flooded (liquid), but offers very good reliability.

hydrogenated amorphous silicon

Amorphous silicon with a small amount of incorporated hydrogen. The hydrogen neutralizes dangling bonds in the amorphous silicon, allowing charge carriers to flow more freely.

a:Si

Amorphous silicon. Silicon material having no definite or regular crystal structure.

peak power current

Amperes produced by a photovoltaic module or array operating at the voltage of the I-V curve that will produce maximum power from the module.

RMS

Amps, excluding the effects of all harmonic exponents; it could be called fundamental power factor

Short circuit

An accidental low-resistance connection between two terminals of a power source that are meant to be at different voltages. A short- circuit is where a power source is connected (at its outlet terminals) by wires without any resistors connected in-between to consume the power. What happens is that very high currents (lots of electrons) flow from the power source directly back into itself. These high currents cause overheating in the power source itself (e.g. in a PV module, the high currents can cause melting of interconnects, or even explosions in a battery because of the chemicals inside). Short circuits also cause fires because sparks, and arcs form and burn combustibles

Net Metering

An agreement between a solar system owner and the local electric utility that allows the system owner to buy and sell energy in the form of electric credits. When the solar system produces excess energy, it is sold back to the electric utility at peak prices, literally causing the electric meter to spin backwards. When the system is not producing energy, the system owner can use the credits to buy back energy at off-peak prices.

Flat‐Plate Module

An arrangement of photovoltaic cells or material mounted on a rigid flat . An arrangement of photovoltaic cells or material mounted on a rigid flat surface with the cells exposed freely to incoming sunlight.

stand-alone (PV system

An autonomous or hybrid photovoltaic system not connected to a grid. May or may not have storage, but most stand-alone systems require batteries or some other form of storage.

Peak Watt (Wp)

the amount of power a photovoltaic module will produce at standard test conditions (normally 1,000 W/m2 and 25° cell temperature).

SUBSTRATE

the material forming the base of the cell beneath the junction or superstrate (the material on the top of the junction). In most wafer cells, the substrate is quite thick and provides physical support. The physical material upon which a photovoltaic cell is applied.

Peak power output (peak output)

the maximum power output possible from a solar module or power system under standard test conditions (stC) is de- fined as the peak power output (also known as peak power). it is measured in watt (w) and stated as watt peak (wp). perform the immediate conversion of light into electrical energy (direct current voltage and current). Also called a solar cell

temperature coefficient

the temperature coefficient is an indication of the degree to which module output changes if the temperature of the solar cell rises.

Ohm (Ω)

the unit of electrical resistance.

Photocurrent:

An electric current induced by radiant energy.

Electric Panel

An electrical distribution board that houses electrical circuit breakers. It is the main point at which electricity is distributed throughout a building. It is otherwise known as a breaker box or electrical cabinet.

ion

An electrically charged atom or group of atoms that has lost or gained electrons; a loss makes the resulting particle positively charged; a gain makes the particle negatively charged

Selenium

An element in the periodic table which has photovoltaic and photoconductive properties

Pyranometer

An instrument used for measuring global solar irradiance

Depletion region

An insulating region within a conductive, doped semiconductor material where the charge carriers have been swept away through recombination. It is also the region at the very centre of a p-n junction where there is no net charge

Module

An integral, encapsulated unit containing a number of PV cells. A group of photovoltaic cells combined in series and/or parallel and encapsulated in an environmentally protective laminate. The smallest replaceable unit in a PV array, modules are the building blocks for arrays.

smart grid

An intelligent electric power system that regulates the two-way flow of electricity and information between power plants and consumers to control grid activity.

DSC - DYE (-Sensitized) SOLAR CELLS

(DSSc, DYSC, Gratzel cells) convert light energy to electricity on a molecular level, similar to natural photosynthesis (it's the first example of an artificial "molecular machine" in a commercial application). A relatively new class of low-cost solar cell, that belong to the group of Thin film solar cells, it is based on a semiconductor formed between a photo-sensitized anode and an electrolyte, a photo electrochemical system.

photovoltaic-thermal

(PV/T) system--A photovoltaic system that, in addition to converting sunlight into electricity, collects the residual heat energy and delivers both heat and electricity in usable form. Also called a total energy system

utility-interactive inverter

An inverter that can function only when tied to the utility grid, and uses the prevailing line-voltage frequency on the utility line as a control parameter to ensure that the PV system's output is fully synchronized with the utility power.

Utility Interactive Inverter

An inverter that can function only when tied to the utility grid, and uses the prevailing line-voltage frequency on the utility line as a control parameter to ensure that the PV systems output is fully synchronised with the utility power

line-commutated inverter

An inverter that is tied to a power grid or line. The commutation of power (conversion from direct current to alternating current) is controlled by the power line, so that, if there is a failure in the power grid, the photovoltaic system cannot feed power into the line.

sine wave inverter

An inverter that produces utility-quality, sine wave power forms.

Fresnel Lens

An optical device that focuses light like a magnifying glass; concentric rings are faced at slightly different angles so that light falling on any ring is focused to the same point.

SOLID-STATE LIGHTING

(SSL): a technology that uses semi-conducting materials to convert electricity into light. A type of lighting that utilizes light-emitting diodes (LEDs), organic light-emitting diodes (OLED), or polymer light-emitting diodes (PLED) as sources of illumination rather than electrical filaments, plasma (used in arc lamps such as fluorescent lamps), or gas. The term "solid-state" refers to the fact that light in an LED is emitted from a solid object (a block of semiconductor) rather than from a vacuum or gas tube, as is the case in traditional incandescent light bulbs and fluorescent lamps.

LIFE-CYCLE COST

(Total Cost of Ownership-TCO) the total costs associated with purchasing, operating, and maintaining a lighting system over its life.

ground loop

An undesirable feedback condition caused by two or more circuits sharing a common electrical line, usually a grounded conductor.

reverse current protection

Any method of preventing unwanted current flow from the battery to the photovoltaic array (usually at night). See also blocking diode.

Subsystem

Any one of several components in a photovoltaic system (i.e., array, controller, batteries, inverter, load).

CIS or CIGS modules

Cis or CiGs modules are a type of thin-film module whose solar cells are made up of several layers of copper indium (gallium) diselenide which are doped with different impuri- ties. efficiency is currently around 12 percent

Satellite Power System (SPS):

Concept for providing large amounts of electricity for use on the Earth from one or more satellites in geosynchronous Earth orbit. A very large array of solar cells on each satellite would provide electricity, which would be converted to microwave energy and beamed to a receiving antenna on the ground. There, it would be reconverted into electricity and distributed the same as any other centrally generated power, through a grid.

reverse bias

Condition where the current producing capability of a PV cell is significantly less than that of other cells in its series string. This can occur when a cell is shaded, cracked, or otherwise degraded or when it is electrically poorly matched with other cells in its string

light-induced defects-

Defects, such as dangling bonds, induced in an amorphous silicon semiconductor upon initial exposure to light

Valence band

Describes electrons in the outer orbit of their atoms and are tied to the atom and not free to move or conduct current. They possess less energy than is required to free themselves and conduct current. The highest energy band in a semiconductor that can be filled withelectrons.

Power supply

Device or system that supplies electrical or other types of energy to an output load or group of loads. The term is most commonly applied to electrical energy supplies

Solar Panel

Devices that collect energy from the sun (solar energy). This is usually solar photovoltaic (PV) modules that use solar cells to convert light from the sun into electricity, or solar thermal (heat) collectors that use the sun's energy to heat water or another fluid such as oil or antifreeze.

deep discharge

Discharging a battery to 20-percent or less of its full charge

EFG

Edge-defined Film-fed Growth. A method for making sheets of polycrystalline silicon in which molten silicon is drawn upward by capillary action through a mold.

Control Circuitry/ Controller

Electric circuit used to monitor and distribute the photovoltaic array output. This usually includes a MPPT, charge controller and regulator and sometimes other more complicated components such as an inverter

Direct current

Electric current that always flows in the same direction: positive to negative. Batteries and photovoltaic cells are all DC devices.

thermal electric

Electric energy derived from heat energy, usually by heating a working fluid, which drives a turbogenerator. See 'solar thermal electric

spinning reserve

Electric power plant or utility capacity on-line and running at low power in excess of actual load.

Fuses

Electrical protection devices that break the electrical circuit if too much current is present. Fuses are particularly important for circuits with batteries, where very large currents can be drawn in the event of a fault or short circuit (over 200 amps depending on the battery type and size). This may damage sensitive electrical devices like microprocessors.

Electrodeposition:

Electrolytic process in which a metal is deposited at the cathode from a solution of its ions.

solar energy

Electromagnetic energy transmitted from the sun (solar radiation). The amount that reaches the earth is equal to one billionth of total solar energy generated, or the equivalent of about 420 trillion kilowatt-hours.

ultraviolet

Electromagnetic radiation in the wavelength range of 4 to 400 nanometers.

Circuit elements

Elements such as resistors, inductors and capacitors which made up a circuit

valence level energy/valence state

Energy content of an electron in orbit about an atomic nucleus. Also called bound state.

Stand-alone system

Energy generated by these systems is stored in batteries and then subsequently used. Also known as "off-grid," these systems are not connected to the utility grid. stand-alone systems (also known as off-grid systems) are photovoltaic systems which are operated independently of the grid and which thus generate a self-sufficient supply of electricity. with these systems, the electricity produced is not fed into the grid but stored in accumulators from where it is sourced for consumption. stand-alone systems are par- ticularly suitable for remote locations in regions with small or unstable grids or for areas where linking up to the grid would not be commercially viable. A solar energy system that is not connected to the utility grid. Also called an off-grid system. To provide continuous power, these systems must be connected to storage units that can store excess power produced during daylight hours for use at night.

Fermi level

Energy level at which the probability of finding an electron is one-half. In a metal, the Fermi level is very near the top of the filled levels in the partially filled valence band. In a semiconductor, the Fermi level is in the band gap.

monolithic

Fabricated as a single structure

Flexible Thin Film Solar

Flexible thin film cells and modules are created by depositing the photoactive layer and other necessary layers on a flexible background material

Conventional current

Flow of positive charge (externally from positive to negative terminal of a generating source). In metal wires, this is opposite in direction to actual physical current that is caused by electrons

Oxidise

For a material to combine chemically with oxygen (often the oxygen already present in air), to produce a new substance with different properties

float-zone process

In reference to solar photovoltaic cell manufacture, a method of growing a large-size, high-quality crystal whereby coils heat a polycrystalline ingot placed atop a single-crystal seed. As the coils are slowly raised the molten interface beneath the coils becomes single crystal.

Float‐Zone Process

In reference to solar photovoltaic cell manufacture, a method of growing a large‐size, high‐quality crystal whereby coils heat a polycrystalline ingot placed atop a single‐crystal seed. As the coils are slowly raised the molten interface beneath the coils becomes a single crystal.

Motor

In this text, a motor refers to a device that converts electrical energy or stored energy in fuel, into rotational energy in a spinning shaft. The spinning shaft can be connected to other devices to cause them to turn as well.

P-N junction

Interface between p-type and n-type silicon. Due to the charge differences between the doped materials, an electric field is set up. Also know as a diode and forms the basis of a solar cell and allows electrons to be collected from within the cell to flow as current

temperature factors

It is common for three elements in photovoltaic system sizing to have distinct temperature corrections: a factor used to decrease battery capacity at cold temperatures; a factor used to decrease PV module voltage at high temperatures; and a factor used to decrease the current carrying capability of wire at high temperatures.

gel-type battery

Lead-acid battery in which the electrolyte is composed of a silica gel matrix.

incident light

Light that shines onto the face of a solar cell or module.

Short wavelength light

Light with higher frequency in the electromagnetic spectrum. Wavelength is the inverse of frequency. The wavelength is the distance of the full-length of the wave in question.

maximum power point

MPP)--The point on the current-voltage (I-V) curve of a module under illumination, where the product of current and voltage is maximum. [UL 1703] For a typical silicon cell panel, this is about 17 volts for a 36 cell configuration.

Insulator

Material that does not allow electric current to pass through easily

MULTICRYSTALINE

Material that is solidified at such as rate that many small crystals (crystallites) form. The atoms within a single crystallite are symmetrically arranged, whereas crystallites are jumbled together. These numerous grain boundaries reduce the device efficiency. A material composed of variously oriented, small individual crystals. (Sometimes referred to as polycrystalline or semicrystalline).

Single Crystal Silicon

Material with a single crystalline formation. Many PV cells are made from single crystal silicon. A type of crystalline silicon which typically has better material parameters but is also more expensive

photovoltaic (PV) peak watt

Maximum "rated" output of a cell, module, or system. Typical rating conditions are 0.645 watts per square inch (1000 watts per square meter) of sunlight, 68 degrees F (20 degrees C) ambient air temperature and 6.2 x 10-3 mi/s (1 m/s) wind speed.

MPP

Maximum Power Point; The point on the current-voltage (I-V) curve of a module under illumination, where the product of current and voltage is maximum. For a typical silicon cell, this is at about 0.45 V.

Underground Feeder (UF):

May be used for photovoltaic array wiring if sunlight‐resistant coating is specified; can be used for interconnecting balance‐of‐system components but not recommended for use within battery enclosures.

Contacts

Metal (usually silver or aluminium) that is deposited on a solar cell to collect the generated carriers (electrons) from the cell and deliver them to a load circuit. There is a top contact (the grid you see on top of a cell) and a rear contact (usually covers the entire back of the cell). The two contacts are electrically separated by the silicon and connect to the circuit to allow current to flow.

grid lines

Metallic contacts fused to the surface of the solar cell to provide a low resistance path for electrons to flow out to the cell interconnect wires.

solar thermal electric

Method of producing electricity from solar energy by using focused sunlight to heat a working fluid, which in turn drives a turbogenerator.

Mismatch

Mismatch losses are caused by the interconnection of solar cells or modules which do not have identical properties or which experience different conditions from one another.

soft costs

Non-hardware costs related to PV systems, such as financing, permitting, installation, interconnection, and inspection.

cycle life

Number of discharge-charge cycles that a battery can tolerate under specified conditions before it fails to meet specified criteria as to performance (e.g., capacity decreases to 80-percent of the nominal capacity).

Polycrystalline

Officially called "multicrystalline," this refers to cast silicon where several crystals form in a mold. SolarWorld's German factories use this casting process as it is less expensive than pulling single crystals, but the resulting cells generally have lower efficiency due to internal resistance along the grain boundaries. Polycrystalline cells can be recognized by a visible grain, a "metal flake effect."

micrometer (micron)

One millionth of a meter.

Voc

Open-circuit voltage

LCPV - LOW CONCENTRATION PHOTOVOLTAICS:

PV systems (with a solar concentration of 2-10 suns) suitable for conventional silicon solar cells. The heat flux is low enough that the cells do not need to be actively cooled. A PV system with a low concentration ratio can have a high acceptance angle and can be installed with or without solar tracker under proper circumstance. A concentration ratio of around 2X produces 2 times more power than regular PV installation. Optical/mechanical structures can be adjusted to meet the different insolation conditions, different latitude and seasons.

i-type semiconductor

Semiconductor material that is left intrinsic, or undoped so that the concentration of charge carriers is characteristic of the material itself rather than of added impurities.

Thick‐Crystalline Materials

Semiconductor material, typically measuring from 200‐400 microns thick, that is cut from ingots or ribbons.

Indirect Bandgap

Semiconductors that have an indirect bandgap are inefficient at emitting light. Electrons require both a photon and a momentum change to move from the valence band to the conduction band

movistor

Short for metal oxide varistor. Used to protect electronic circuits from surge currents such as those produced by lightning.

Kerf losses

Silicon 'sawdust' that is generated and lost when you saw an ingot to cut individual wafers out of it.

Silicon carbide

Silicon carbide (SiC), silicon bonded with carbon, is another member of the silicon family of materials used in the PV industry. It is a common abrasive in many industries, used in everything from grinding to sandblasting. At SolarWorld, crushed SiC is mixed into a water slurry and applied to saw wires. Silicon carbide, not wire, actually does the cutting

Unencapsulated

Solar cells that have not been integrated into a module that would protect them from natural elements such as water, oxygen, dust

Watt-hours

Sometimes called watt. The amount of watts used by an appliance is an hour.

Storage

Storage refers to saving surplus electricity produced by a PV system. Generally batteries are used as storage devices.

Tracking equipment

Structure that houses PV modules and that can automatically follow the sun across the sky throughout the day to maximize output.

direct insolation

Sunlight falling directly upon a collector. Opposite of diffuse insolation.2 The radiant energy from the sun (and a small area of sky surrounding it, defined by the acceptance angle of the pyrheliometer) incident upon unit surface area during a specified time period. (MJ/m2 per hour, day, week, month or year, as the case may be).

disconnect

Switch gear used to connect or disconnect components in a photovoltaic system.

Electrical distribution system

System of delivery of electricity to the end user. The most common form of distribution is the 'electricity grid' - a network of transmission lines (wires) connecting generators to loads.

remote systems

Systems off of the utility grid. Out in the boondocks

Distributed Systems

Systems that are installed at or near the location where the electricity is used, as opposed to central systems that supply electricity to grids. A residential photovoltaic system is a distributed system

stand-off mounting

Technique for mounting a photovoltaic array on a sloped roof, which involves mounting the modules a short distance above the pitched roof and tilting them to the optimum angle.

Maximum Power Point or Peak Power Point

That point on an I-V curve that represents the largest area rectangle that can be drawn under the curve. Operating a Solar PV array at that voltage will produce maximum power

ramp rate

The ability of a generating unit to change its output over some unit of time, often measured in MW/min.

Volt

The amount of force required to drive a steady current of one ampere through a resistance of one ohm. Electrical systems of most homes and offices use 120 volts. (Volts = watts/amps)

reserve capacity

The amount of generating capacity a central power system must maintain to meet peak loads

electron volt (eV)

The amount of kinetic energy gained by an electron when accelerated through an electric potential difference of 1 Volt; equivalent to 1.603 x 10^-19; a unit of energy or work.

Peak watts

The amount of power a photovoltaic device will produce at noon on a clear day with sun approximately overhead when the cell is faced directly toward the sun.

Rated power or power rating

The amount of power a resistive circuit element or electrical device can withstand flowing through it. It is also the power that a device may generate if it's a power source. Manufacturers provide power ratings for devices they produce, and they are likely to fail if this rating is exceeded.

duty rating

The amount of time an inverter (power conditioning unit) can produce at full rated power.

Energy Payback

The amount of time required for a solar panel to generate the amount of energy it took to manufacture it. Modern PV panels have an energy payback of 1 to 3 years depending on where they're installed; over a 30+ year life, a PV system will return 10 to 30 times the energy that went into making them.

depth of discharge (DOD)

The ampere-hours removed from a fully charged cell orbattery, expressed as a percentage of rated capacity. For example, the removal of 25 ampere-hours from a fully charged 100 ampere-hours rated cell results in a 25% depth of discharge. Under certain conditions, such as discharge rates lower than that used to rate the cell, depth of discharge can exceed 100%.

tilt angle

The angle at which a photovoltaic array is set to face the sun relative to a horizontal position. The tilt angle can be set or adjusted to maximize seasonal or annual energy collection.

Packing density

The area of the module that is covered with solar cells compared to that which is blank. The packing density affects the output power of the module as well as its operating temperature. The packing density depends on the shape of the solar cells used

state of charge (SOC)

The available capacity remaining in the battery, expressed as a percentage of the rated capacity.

Minority Carrier Lifetime:

The average time a minority carrier exists before recombination

boron (B)

The chemical element commonly used as the dopant in photovoltaic device orcell material

Amorphous

The condition of a solid in which the atoms are not arranged in an orderly pattern.

Break-even

The cost of a photovoltaic system at which the cost of the electricity it produces exactly equals the price of electricity from a competing source.

superstrate

The covering on the sunny side of a photovoltaic (PV) module, providing protection for the PV materials from impact and environmental degradation while allowing maximum transmission of the appropriate wavelengths of the solar spectrum. 2 Commonly used in thin-film cells, where the thick glass layer acts as the substrate, but it actually covers the front surface of the cell where the sunlight should come in. So, when manufacturing, we lay down the glass first, then the front layer, and then the rest of the cell. Then we flip it over when ready to use.

charge rate

The current applied to a cell or battery to restore its available capacity. This rate is commonly normalized by a charge control device with respect to the rated capacity of the cell or battery. Chemical etch The process of using

short-circuit current (Isc

The current flowing freely from a photovoltaic cell through an external circuit that has no load or resistance; the maximum current possible.

rated module current (A)

The current output of a photovoltaic module measured atstandard test conditions of 1,000 w/m2 and 25°C cell temperature. the current output of a PV module measured at standard test conditions of 1,000 W/m2 and 25°C cell temperature

Short circuit current

The current through the solar cell when the voltage across the solar cell is zero (i.e., when the solar cell is short circuited)

scribing

The cutting of a grid pattern of grooves in a semiconductor material, generally for the purpose of making interconnections.

Uninterruptible Power Supply (UPS)

The designation of a power supply providing continuous uninterruptible service. The UPS will contain batteries. A device which maintains a continuous supply of electric power to connected equipment by supplying power from a separate source when utility power is not available.

Irradiance

The direct, diffuse, and reflected solar radiation that strikes a surface. Usually expressed in kilowatts per square meter. Irradiance multiplied by time equals insolation.

AC (Alternating Current)

The direction of electrical current reverses, usually many (60) times per second. Electricity transmission networks use AC because voltage can be controlled with relative ease.

POWER CONDITIONER

The electrical equipment used to convert power from a photovoltaic array into a form suitable for subsequent use. Loosely, a collective term for inverter, transformer, voltage regulator and other power controls.

Grid

The electricity transmission and distribution system that links power plants to customers through high-power transmission line service.

Photoelectric effect

The emission of electrons from most surfaces that occurs when light (photons) hits them

work function

The energy difference between the Fermi level and vacuum zero. The minimum amount of energy it takes to remove an electron from a substance into the vacuum.

Vacuum Zero:

The energy of an electron at rest in empty space; used as a reference level in energy band diagrams.

normal operating cell temperature (NOCT)

The estimated temperature of a photovoltaic when operating under 800 w/m2 irradiance, 20°C ambient temperature and wind speed of 1 meter per second. NOCT is used to estimate the nominal operating temperature of a module in its working environment.

gassing

The evolution of gas from one or more of the electrodes in the cells of a battery. Gassing commonly results from local action self-discharge or from the electrolysis of water in the electrolyte during charging

Crystallinity

The extent to which a material exhibits the properties of a crystal. If an entire silicon ingot is made of just one crystal, this is the highest level of crystallinity possible. If we observe scattered atoms that show no order that you would find in crystals, then we say the material has very low crystallinity.

Electrical Current

The flow of charged electrons through a circuit. Depending upon its behavior, an electrical current can be alternating or direct (AC or DC).

Current 1

The flow of electric charge in a conductor between two points having a difference in potential (voltage).2 The amount of electric charge flowing through a surface over time (amount of charge per second)

FULL SUN

The full sun condition is the amount of power density received at the surface of the earth at noon on a clear day - about 100 mW/cm2. Lower levels of sunlight are often expressed as 0.5 sun or 0.1 sun. A figure of 0.5 sun means that the power density of the sunlight is one-half of that of a full sun.

scheduling

The general practice of ensuring that a generator is committed and available when needed. It also can refer to scheduling of imports or exports of energy into or out of abalancing area.

Epitaxial Growth

The growth of one crystal on the surface of another crystal. The growth of the deposited crystal is oriented by the lattice structure of the original crystal.

Azimuth

The horizontal angle measured from true north, in a clockwise direction

Cloud Enhancement

The increase in solar intensity caused by reflected irradiance from nearby clouds.

square wave inverter

The inverter consists of a dc source, four switches, and the load. The switches are power semiconductors that can carry a large current and withstand a high voltage rating. The switches are turned on and off at a correct sequence, at a certain frequency. The square wave inverter is the simplest and the least expensive to purchase, but it produces the lowest quality of power.

shelf life of batteries

The length of time, under specified conditions, that a battery can be stored so that it keeps its guaranteed capacity.

Demand

The level at which electricity (or natural gas) is delivered to end-users at a given point in time. Electric demand is measured in kilowatts.

Donor Level

The level that donates conduction electrons to the system.

peak demand/load

The maximum energy demand or load in a specified time period.

Peak Load

The maximum load demand on a Solar PV system

peak load; peak demand

The maximum load, or usage, of electrical power occurring in a given period of time, typically a day.

Open Circuit Voltage

The maximum voltage produced by an illuminated photovoltaic cell, module, or array with no load connected. This value will increase as the temperature of the PV material decreases. connected (there is no current passing through the cell -zero current).

Diffusion Length

The mean distance a free electron or hole moves before recombining with another hole or electron.

total harmonic distortion

The measure of closeness in shape between a waveform and it's fundamental component.

Pulse width modulation

The modulation of signal's or power source's duty cycle, to either convey information over a communications channel or control the amount of power sent to a load

Design Month

The month having the combination of insolation and load that requires the maximum energy from the photovoltaic array. determinable) frequency. For example in Australia our AC network is 50Hz or 50 cycles per second, which means that, 50 times each second the current flows one way and 50 times per second current flow in reverse

Projected Area

The net south‐facing glazing area projected on a vertical plane

days of storage

The number of consecutive days the stand-alone system will meet a defined load without solar energy input. This term is related to system availability.

Frequency

The number of cycles through which an alternating current moves in each second. Standard electric utility frequency in the United States is 60 cycles per second, or 60 hertz. The number of repetitions per unit time of a complete waveform, expressed in Hertz (Hz).

Battery Cycle Life

The number of cycles, to a specified depth of discharge, that a cell or battery can undergo before failing to meet its specified capacity or efficiency performance criteria.

harmonic content

The number of frequencies in the output waveform in addition to the primary frequency (50 or 60 Hz.). Energy in these harmonic frequencies is lost and may cause excessive heating of the load.

Frequency (electrical)

The number of wavelength cycles a photon or an oscillating AC signal passes through in one second. It is given in the SI units, Hertz (Hz). Most electricity grids operate on 50Hz (Global) or 60Hz (US and Japan).

float life

The number of years that a battery can keep its stated capacity when it is kept at float charge.

electric circuit

The path followed by electrons from a power source (generator or battery), through an electrical system, and returning to the source.

wet shelf life

The period of time that a charged battery, when filled with electrolyte, can remain unused before dropping below a specified level of performance.

PHOTOVOLTAIC EFFECT 2

The phenomenon that occurs when photons, the "particles" in a beam of light, knock electrons loose from the atoms they strike. When this property of light is combined with the properties of semiconductors, electrons flow in one direction across a junction, setting up a voltage. With the addition of circuitry, current will flow and electric power will be available. A process or effect that generates voltage in a solar cell. The conversion of sunlight absorbed by a solar cell directly into electricity.

system operating voltage

The photovoltaic array output voltage under load. The system operating voltage is dependent on the load or batteries connected to the output terminals.

Maximum Power Point (MPP):

The point on the current‐voltage (I‐V) curve of a module under illumination, where the product of current and voltage is maximum. For a typical silicon cell, this is at about 0.45 volts

anode

The positive electrode in an electrochemical cell (battery). Also, the earth or ground in a cathodic protection system. Also, the positive terminal of a diode. The positive terminal of a diode.

MAXIMUM POWER

The power at the point on the current-voltage characteristic where the product of current and voltage is a maximum (measured in watts).

locational marginal price (LMP)

The price of a unit of energy at a particular electrical location at a given time. LMPs are influenced by the nearby generation, load level, and transmission constraints and losses

Crystallisation

The process by which a liquid substance forms a very neatly structured solid crystal when it is cooled sufficiently slowly. Only some substances form such crystals.

recombination

The process by which electrons already in the conduction band fall back to a lower energy position in the valence band The action of a free electron falling back into a hole. Recombination processes are either radiative, where the energy of recombination results in the emission of a photon, or nonradiative, where the energy of recombination is given to a second electron which then relaxes back to its original energy by emitting phonons. Recombination can take place in the bulk of the semiconductor, at the surfaces, in the junction region, at defects, or between interfaces.

Passivation

The process of incorporating materials in the solar cell to make open bonds chemically inactive. That is, they will not interact with impurities that may be present in the semiconductor material and this therefore prevents electrical performance degradation . A chemical reaction that eliminates the detrimental effect of electrically reactive atoms on a solar cell's surface

Doping2

The process of intentionally introducing impurities into an extremely pure semiconductor in order to change its electrical properties. It is done by introducing a dopant (e.g. other elements) into the semiconductor in order to alter the conduction properties. It allows conductivity to be controlled by creating an excess of positive or negative charge carriers

Equalization Charge

The process of mixing the electrolyte in batteries by periodically overcharging the batteries for a short time.

power conditioning

The process of modifying the characteristics of electrical power (for e.g., inverting direct current to alternating current

EQUALIZATION

The process of restoring all cells in a battery to an equal state-of-charge. For lead-acid batteries, this is a charging process designed to bring all cells to 100% state-of- charge. Some battery types may require a complete discharge as a part of the equalization process.

Chemical etch

The process of using chemicals such as acid and bases to dissolve away unwanted materials such as metals, grease

demand response

The process of using voluntary load reductions during peak hours

Extrinsic Semiconductor

The product of doping a pure semiconductor

resistance (R)

The property of a conductor, which opposes the flow of an electric currentresulting in the generation of heat in the conducting material. The measure of the resistance of a given conductor is the electromotive force needed for a unit current flow. The unit of resistance is ohms

DIFFUSE INSOLATION

The radiant energy from the sky incident upon unit surface area during a specified time period (Same units as for direct insolation). 2 --Sunlight received indirectly as a result of scattering due to clouds, fog, haze, dust, or other obstructions in the atmosphere. Opposite of direct insolation.

self discharge

The rate at which a battery, without a load, will lose its charge. This can vary considerably depending on the type of battery and age. It can be as low as 3% a month for a new AGM battery, and as high as 10% a week for an older Lead-Antimony (industrial) battery.

watt

The rate of energy transfer equivalent to one ampere under an electrical pressure of one volt. One watt equals 1/746 horsepower, or one joule per second. It is the product ofvoltage and current (amperage).

packing factor

The ratio of array area to actual land area or building envelope area for a system; or, the ratio of total solar cell area to the total module area, for a module.

energy density

The ratio of available energy per pound; usually used to compare storage batteries. 2 --The ratio of energy available from a battery to its volume (Wh/1) or mass (Wh/kg). "watts to weight" ratio.

photovoltaic (PV) efficiency

The ratio of electric power produced by a cell at any instant to the power of the sunlight striking the cell. This is typically about 9% to 14% for commercially available cells.

photovoltaic (PV) conversion efficiency

The ratio of the electric power produced by a photovoltaic device to the power of the sunlight incident on the device.

quantum efficiency (QE)

The ratio of the number of charge carriers collected by a photovoltaic cell to the number of photons of a given energy shining on the cell. Quantum efficiency relates to the response of a solar cell to the different wavelengths in the spectrum of light shining on the cell. QE is given as a function of either wavelength or energy. Optimally, a solar cell should generate considerable electrical current for wavelengths that are most abundant in sunlight.

power density

The ratio of the power available from a battery to its mass (W/kg) or volume (W/l).

specific gravity

The ratio of the weight of the solution to the weight of an equal volume of water at a specified temperature. Used as an indicator of battery state-of-charge.

homojunction

The region between an n-layer and a p-layer in a single material, photovoltaic cell.

electron hole pair

The result of light of sufficient energy dislodging an electron from its bond in a crystal, which creates a hole. The free electron (negative charge) and the hole (positive charge) are a pair. These pairs are the constituents of electricity.

BATTERY CELL

The simplest operating unit in a storage battery. It consists of one or more positive electrodes or plates, an electrolyte that permits ionic conduction, one or more negative electrodes or plates, separators between plates of opposite polarity, and a container for all the above.

photovoltaic (PV) module

The smallest environmentally protected, essentially planar assembly of solar cells and ancillary parts, such as interconnections, terminals, (and protective devices such as diodes) intended to generate direct current power under unconcentrated sunlight. The structural (load carrying) member of a module can either be the top layer (superstrate) or the back layer (substrate).

MODULE

The smallest non divisible, self-contained and environmentally protected physical structure housing interconnected Photovoltaic cells and providing a single DC electrical output.

Atoms

The smallest particle of an element that can exist either alone or in combination

total internal reflection

The trapping of light by refraction and reflection at critical angles inside a semiconductor device so that it cannot escape the device and must be eventually absorbed by the semiconductor.

light trapping

The trapping of light inside a semiconductor material by refracting and reflecting the light at critical angles; trapped light will travel further in the material, greatly increasing the probability of absorption and hence of producing charge carriers.

Equinox

The two times of the year when the sun crosses the equator and night and day are of equal length; usually occurs on March 21st (spring equinox) and September 23rd (fall equinox).

modularity

The use of multiple inverters connected in parallel to service different loads.

Multijunction cell

The use of multiple layers of silicon, doped with alternating p and n layers to create multiple p-n junctions. Each layer of silicon is optimized to absorb a different part of the solar spectrum, thereby increasing the overall collection efficiency of the PV device.

Solar Cooling

The use of solar thermal energy or solar electricity to power a cooling appliance. Photovoltaic systems can power evaporative coolers (swamp coolers), heat pumps, and air conditioners.

Climate change

The variation in the Earth's global climate or regional climates over time. It describes changes in the variability or average state of the atmosphere over time scales ranging from decades to millions of years. These changes can be caused by processes internal to the Earth, external forces (e.g. variations in sunlight intensity) or, more recently, human activities

High Voltage Disconnect

The voltage at which a charge controller will disconnect the photovoltaic array from the batteries to prevent overcharging

voltage at maximum power (Vmp)--

The voltage at which maximum power is available from a module. [UL 1703]

resistive voltage drop

The voltage developed across a cell by the current flow through the resistance of the cell.

high voltage disconnect hysteresis

The voltage difference between the high voltag disconnect set point and the voltage at which the full photovoltaic array current will be reapplied.

low voltage disconnect hysteresis

The voltage difference between the low voltage disconnect set point and the voltage at which the load will be reconnected.

cutoff voltage

The voltage levels (activation) at which the charge controller disconnects the photovoltaic array from the battery or the load from the battery.

float charge

The voltage required to counteract the self-discharge of the battery at a certain temperature.

Parallel

The voltages across components in parallel with each other are the same in magnitude and they also have identical polarities.

Million Solar Roofs Initiative

This is a state of California initiative to facilitate the installation of solar energy systems on one million US buildings by 2010. This initiative is largely responsible for the rebates and incentives available in California and serves as a model for many other state solar programs

input voltage

This is determined by the total power required by the alternating currentloads and the voltage of any direct current loads. Generally, the larger the load, the higher the inverter input voltage. This keeps the current at levels where switches and other components are readily available.

standby current

This is the amount of current (power) used by the inverter when no loadis active (lost power). The efficiency of the inverter is lowest when the load demand is low.

True sine wave

This is the shape of an ideal AC waveform (sinusoidal). It's the most desirable output of an inverter, producing no damage to appliances that utilise the AC electricity

Open-circuit

This is when a circuit is cut. Think of an electric cable that has been cut by scissors. This is an open circuit. Voltages in circuits are sometimes measured across an open circuit (use multimeter leads to reconnect cut cable)

Energy level

This refers to the amount of energy that an electron may actually possess. There are ranges of energy levels that electrons in semiconductors may have, and we call these ranges, "bands"

Modified square wave

This waveform is a compromise between the sine wave and the square wave. The positive and negative pulses of the square wave are thinned, separated and made taller, so the peak voltage is much closer to that of a sine wave, and the overall shape of the wave more closely resembles that of a sine wave.

Triple Junction

Three extremely thin single junction cells, with different bandgaps, stacked on top of one another

Energy/Energise

To supply or transfer enough energy to an object (e.g. an electron) to allow it to do work. If something has energy, it means it is capable of doing work or transferring that energy to another object which could use that energy to do work. Energy is measured in Joules (SI unit) ,kilowatt-hours (kWh).

shunt regulator

Type of a battery charge regulator where the charging current is controlled by a switch or transistor connected in parallel with the PV panel. Overcharging of the battery is prevented by shorting the PV output. Shunt regulators are common in PV systems as they are relatively cheap to build and simple to design. Series regulators usually have better control and charge characteristics. Most newer controllers have gone to series regulation.

series regulator

Type of battery charge regulator where the charging current is controlled by a switch, transistor, or FET connected in series with the PV module or array. As opposed to a shunt regulator, which gradually shorts out the panel output as the battery gets charged up.

Deep Cycle

Type of battery that can be discharged to a large fraction of capacity many times without damaging the battery.

Langley (L):

Unit of solar irradiance. One gram calorie per square centimeter. 1 L = 85.93 kwh/m2.

Transparency

We describe a material as being transparent if it lets through most of the light that falls on it (e.g. window glass is transparent to short wavelength radiation but not long wavelength radiation). This means the wavelengths of light that pass through can be absorbed by materials/things behind the transparent one.

Black-outs

When generators that were supplying an electricity grid fail and cause loss of power to loads and buildings that require it

Interconnection

With regard to PV modules, this refers to the connection of the individual cells that make up the module. The bottom of one cell is connected by metal wires to the top of the next cell

Junction Box

a PV generator junction box is an enclosure on the module back side, where electrical contacts and protection devices (if used) are located.

Silicon (Si)

a chemical element, atomic number 14, semimetallic in nature, dark gray, an excellent semiconductor material. A common constituent of sand and quartz (as the oxide). The most common semiconductor material used in making photovoltaic devices. A semi-metallic chemical element that makes an excellent semiconductormaterial for photovoltaic devices. It crystallizes in face-centered cubic lattice like a diamond. It's commonly found in sand and quartz (as the oxide). The basic material used to make solar cells. It is the second most abundant element in the earth's crust, after oxygen.

Panel

a designation for a number of PV modules assembled in a single mechanical frame.

flagship project

a flagship project is a completed project which, along with its original purpose, is considered to be exemplary and set a benchmark for the whole sector. the reasons may be the successful deployment of new technologies, new areas of application or new yardsticks set in respect of yield and re- turn.

PRODUCTIVITY

a measure of the rate at which output flows from the use of given amounts of inputs. Productivity is usually measured by expressing output as a ratio to a selected input (labour productivity, capital productivity).

MICROMORPHOUS SILICONE:

a module technology that combines two different types of silicon, amorphous and microcrystalline silicon, in a top and a bottom photovoltaic cell. These are so-called tandem cells of two ultra-thin silicon layers on top of each other; because both silicon structures absorb

operation

along with configuration and system integration, the com- mercial and technical operation of solar power plants are key factors influencing the yield and therefore the return. Core tasks are to secure steady-state optimal operation, the monitoring and reporting of yield data, as well as compli- ance with the statutory provisions and periodic inspections

CIRCUIT BREAKER

an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and to immediately discontinue electrical flow. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.

Electron-volt (eV)

an energy unit equal to the energy an electron acquires when it passes through a potential difference of one volt; it is equal to 1.602 x 10-19 V.

Pyrheliometer

an instrument used for measuring direct beam solar irradiance. Uses an aperture of 5.7° to transcribe the solar disc. An instrument for measuring total hemispherical solar irradiance on a flat surface, or "global" irradiance; thermopile sensors have been generally identified as pyranometers,however, silicon sensors are also referred to as pyranometers.

PROJECT

an integrated set of activities geared to attain specific objectives and goals, having defined resources (human, physical, equipment, material and information), a specific budget, responsible persons/institutions and a given time frame.

Electrical grid

an integrated system of electricity distribution, usually covering a large area. 2 - Often just called, "the grid." This refers to the network of cables & high-power electrical devices used to deliver power from the generators to the loads (residential, industrial etc.)

MONOCRYSTALLINE (wafer-based) SOLAR CELLS

are cut from a silicon boule that is grown from a single crystal, i.e. a crystal that has grown in only one plane (one direction); semiconductor grade silicon is melted and, through a crystal seeding process, a large single silicon crystal is formed. A phosphorous impurity is introduced into the surface layers of the wafer and metal grids are attached to the front and back of the wafer to facilitate the collection of electrons. Monocrystalline cells tested in the laboratory have given efficiencies of over 23%. Monocrystalline cells are used in the more expensive types of solar panels and are more efficient than polycrystalline cells in converting the sun's rays to electricity. Monocrystalline and polycrystalline cells work well in bright cool conditions, whereas thin-film (amorphous) silicon cells are more efficient at higher temperatures.

N-type Semiconductors

are extrinsic semiconductors with a larger electron concentration than hole concentration.

String inverters

are the most common type of inverter for residential and small commercial PV systems.

HIGH TECH FIRMS

business units producing goods and services whose competitiveness depends on the design, development and production of new products or innovative processes, through the systematic and intensive application of scientific and technological knowledge.

Micro inverters

can be installed on each solar module. The cost is typically higher, but they provide certain advantages for very small or geometrically complex PV systems.

OLED - Organic LED

diodes based on organic (carbon) materials. OLEDs are made in sheets which provide a diffuse area light source. OLED technology is developing rapidly and is increasingly used in display applications such as cell phones and PDA screens. However, OLEDs are still some years away from becoming a practical general illumination source. Additional advancements are needed in light output, colour, efficiency, cost, and lifetime.

amperage interrupt capability (AIC)

direct current fuses should be rated with a sufficient AIC to interrupt the highest possible current.

Private consumption

electricity produced by a solar power system can also be used for one's own consumption, alongside feeding into the public grid. under the German Renewable energies act (eeG), each kilowatt hour produced and used for private consumption will be remunerated in an amount of 16.74 cent as from 1 January 2011.

LIGHT

electromagnetic radiation that stimulates sight and makes things visible (from about 390 to 740 nm in wavelength). Most of the spectrum is ultraviolet, visible light and infra red. Photovoltaic cells can use most of this radiation and convert it to electricity. At the sunward surface of the cell the highest possible average incident solar radiation is about 1000 W/m2.

DC/DC Converter

electronic cirquit that converts DC voltages into other levels. Usually it is part of a maximum power point trackers (MPPT) and charge regulators.

EVA - Ethylene-vinyl Acetate

film used in the production of solar panels; it is specifically used for the encapsulation of the cells. This encapsulation process is known as lamination. EVA is hard-wearing, transparent, resistant to corrosion, and flame retardant.

P-N Junction

is a boundary or interface between two types of semiconductor material, p-type and n-type, inside a single crystal of semiconductor. It is created by doping.

Charge Carriers

is a particle free to move, carrying an electric charge, especially the particles that carry electric charges in electrical conductors. Examples are electrons, ions and holes.

Wafer

is a thin slice of semiconductor material, such as a silicon crystal, used in the fabrication of integrated circuits and other microdevices.

Diode

is a two-terminal electronic component with asymmetric conductance; it has low (ideally zero) resistance to current in one direction, and high (ideally infinite) resistance in the other.

Band Gap

is an energy range in a solid where no electron states can exist.

Recombination Lifetime

is defined as the average time it takes for a minority carrier to recombine. The process through which this is done is typically known as minority carrier recombination.

Nominal Cell Operating Temperature

is defined as the temperature reached by open circuited cells in a module under these conditions: irradiance on cell surface = 800 W/m2, air temperature = 20°C, wind velocity = 1 m/s.

Photovoltaic Effect

is the creation of voltage or electric current in a material upon exposure to light.

Short-circuit Current

is the current through the solar cell when the voltage across the solar cell is zero.

Valence Band

is the highest range of electron energies in which electrons are normally present at absolute zero temperature.

LIGHT OUTPUT:

luminous flux, measured in lumens. The light output rating of a lamp is a measure of its total integrated light output.

POLYCRYSTALLINE (wafer-based) SOLAR CELLS:

made out of polycrystalline materials [cadmium telluride (CdTe) and copper indium (gallium) diselenide (CIS or CIGS)] composed of many crystallites of varying size and orientation. Manufacturers have pioneered processes for mass-producing inexpensive poly crystalline cells, taking advantage of the fact that it is inherently easier to grow little crystals than big ones. A disadvantage of polycrystalline cells is that the boundaries between the tiny crystals tend to impede the flow electrons through the material (18% efficiency). The new silicon nitride polycrystalline cells have higher efficiency than similarly sized monocrystalline cells. Monocrystalline and polycrystalline cells work well in bright cool conditions, whereas thin-film (amorphous) silicon cells are more efficient at higher temperatures.

MOS-FET

metal-oxid-silicon field effect transistor; used as semiconductor power switch in charge regulators, inverters etc.

Micromorphous modules

micromorphous modules (also known as tandem modules) combine both amorphous and microcrystalline technolo- gies. the light spectrum absorbed is raised to the near-in- frared region through an additional microcrystalline layer of silicon applied to an amorphous silicon layer. micromor- phous modules are therefore more efficient than amorphous modules.

NOCT

nominal operating cell temperature. The estimated temperature of a PV module when operating under 800 W/m2 irradiance, 20°C ambient temperature and wind speed of 1 m/s. NOCT is used to estimate the nominal operating temperature of a module in its working environment.

nominal output

nominal output (also known as peak output) is an indication of the output of a solar module or a solar power plant, for instance.

photovoltaic (PV) panel

often used interchangeably with PV module (especially in one-module systems), but more accurately used to refer to a physically connected collection of modules (i.e., a laminate string of modules used to achieve a required voltage and current).

MOTION SENSOR LIGHTING CONTROL

sensors that detect movement and automatically turn lights on and turn them off a short while later. Because utility lights and some security lights are needed only when it is dark and people are present, the best way to control might be a combination of motion sensor and photosensor.

Polycrystalline cells

the basic material for polycrystalline (also known as multi- crystalline) cells is ultra-pure silicon. liquid silicon for poly- crystalline cells is first cast as ingots and then cut into wafers which are 0.2 to 0.4 millimetres thick. the cells that result from this process are made up of many small single crystals, so-called crystallites, which are separated by grain bounda- ries. the pattern which results from the composition of dif- ferent crystals is unmistakable, as is the bluish colour.

Waveform

the characteristic shape of an AC current or voltage output. The shape of the phase power at a certain frequency and amplitude.

COST PER WATT - CPW ($/W):

the cost of the electric power output that a solar installation generates under average conditions ($/W). It provides a basis for comparison among photovoltaic technologies and between installations, as well as between solar energy and other sources of electricity. It's probably the most important metric in the solar industry, although it fails to take into account the amount of usable energy that is generated by a given solar installation. That cost is better (and more accurately) measured in terms of S/kWh (not $/W). Different photovoltaic installations having the same $/W often have different average daily power output, leading to widely varying $/kWh. To improve CPW, manufacturers can either reduce cost (by improving yield, increasing throughput, and other variables in the manufacturing process) or increase the wattage available from a given panel area. In turn, increasing output power requires improved conversion efficiency: the panel must capture more incident photons, convert more of them to free carriers, and deliver more of those carriers to the panel's terminals. The average daily electric power output of a solar photovoltaic system is approximately equal to its power output multiplied by the average peak hours of sunlight (roughly around 4-5 hours/day, or 40-50% of direct sunlight hours). Watt-peak (Wp) is the amount of power that a PV module is able to supply when it receives 1000 W/m2 of solar radiation. Photovoltaic systems can produce power at less cost than some traditional electricity sources (diesel electric generators). A barrel of oil (159 I) produces 1700 KWH, at $70/barrel (Aug.09): $0.05/kWh [1m3 of gas generates 10.59 kWh, at $0.29/m3: 0.03 kWh]; however, this is only the cost of energy generation: capital eguipment costs (power plant) are not taken into account, neither the transmission losses from the central power plant to the consumer.

Operating point

the current and voltage that a module or array produces when connected to a load. The operating point is dependent on the load or the batteries connected to the output terminals of the array.

Load current

the current required by the electrical device (load).

LUMEN DEPRECIATION

the decrease in lumen output that occurs as a lamp is operated, until failure.

Absorption coefficient

the factor by which photons are absorbed as they travel a unit distance through a material.

Grid parity

the grid parity of solar electricity means that the price of generating one kilowatt hour of solar electricity is no higher than the end consumer price for electricity from the mains socket. Grid parity is therefore tied to the location of con- sumption, as solar electricity is often generated where it is consumed. the definition of grid parity is not therefore a comparison between the production costs of solar electric- ity and those of energy generated from fossil-based sources. 1,000 w/m2.

Monocrystalline cells

the input material for monocrystalline cells is ultra-pure sili- con which is extracted from silicon smelt and fabricated into wafers of up to twelve centimetres in diameter. all crystal lattices are evenly distributed in monocrystalline. monocrys- talline cells are more efficient than polycrystalline cells but are also more expensive to manufacture. they can be recog- nised by their characteristic graphite colour

INITIAL DEGRADATION

the loss of efficiency in solar photovoltaic cells.

LUMINANCE

the measured brightness of a light source or of an illuminated surface that reflects light (cd/m2)

LUX

the metric unit of measure for illuminance of a surface (Ix = 1 lm/ m2).

Depth of discharge

the percent of the rated battery capacity that has been withdrawn. Sometimes also expressed as abbreviation DoD.

Resistance

the property of a conductor which opposes the flow of an electric current resulting in the generation of heat in the conducting material

ENCAPSULATION

the protection placed around the cells when modules are made. Encapsulation has been designed to last at least 20 years and therefore protect the cells for that period to ensure proper operation of the module.

LUMINOUS FLUX

the rate of flow of light, measured in lumens. The overall light output of a lamp.

EFFICIENCY

the ratio of the electrical power output Pout, compared to the solar power input, Pin, into the PV cell. Pout can be taken to be PMAX since the solar cell can be operated up to its maximum power output to get the maximum efficiency. 2 In regards to solar cells, it describes the amount of electrical energy produced as a fraction of the light energy received by the cell as a percentage. This is the key measure of cell performance

RADIOMETRY

the science of the measurement of radiant energy (including light) in terms of absolute power.

Standard test Conditions (StC)

the specific data of a solar module are measured under standard test conditions. standard test conditions are de- fined as the solar irradiation of one kilowatt (kw) per square metre, a module temperature of 25 degrees Celsius and a solar irradiation angle of 45 degrees.

DC - Direct Current

the unidirectional flow of electric charge. Direct current may flow in a conductor such as a wire, but can also be through semiconductors, insulators, or even through a vacuum as in electron or ion beams. Direct current may be obtained from an alternating current supply by use of a rectifier (a current-switching arrangement); and it may be made into alternating current with an inverter.

Value chain

the value chain is the whole mix of products and services which go to make up one product (solar power plant) or a service (system integration, operation), comprising all links in the chain, also including suppliers of raw materials and manufacturers, across system integrators and wholesalers and retailers through to the end customer.

Finger

thin strips placed between cells. The most commonly used strips are tin-coated copper.

LUMEN

unit of luminous flux, a measure of the perceived power of light. Luminous flux differs from radiant flux, the measure of the total power of light emitted, in that luminous flux is adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light. The lumen is defined in relation to the candela (unit of luminous intensity, describing the intensity of a light source in a specific direction). The lumen rating of a lamp is a measure of the total light output of the lamp.

TCO - TRANSPARENT CONDUCTIVE OXIDE

used as conductive 'window layer' in thin film technology, as well as for photoelectrochemical solar cells (zinc oxide, indium tin oxide).

CONCENTRATING PHOTOVOLTAICS - CPV:

uses lenses or mirrors to focus or increase the sun's light on a photovoltaic solar cell or panel. CPV systems aim to reduce overall cost by reducing the amount of semiconductor needed. A panel incorporating 10* magnifying lenses can capture the same amount of light as a standard panel, but with one-tenth of the semiconductor area. Lenses are relatively inexpensive, while semiconductor material is the most expensive component of a panel. CPV lenses can range from 5* concentration to 500* or more. Because of their reliance on lenses, CPV systems work best in direct sunlight; power output drops sharply on overcast days, or even if a cloud passes over the sun. If the angle between the incident light and the lens changes, the lens will focus less light onto the centre of the cell. Systems with concentrations of 10x or more normally use tracking mechanisms to follow the sun across the sky. High concentration systems may also need active cooling and high capacity heat sinks. High concentration HCPV technology can increase the sun's magnification by hundreds of suns; it uses focusing lenses to concentrate the sun's rays on a single, high efficiency solar cell that is very small, on the order of 1cm2 (PV efficiency over 40%: HCPV technology provides nearly 3 times the economic revenues of any 12-15% efficient PV panel). Low-concentration LCPV technology increases the sun's magnification by less than 5 "suns". At the sunward surface of the cell the highest possible average incident solar radiation is about 1000 W/m2.

Kilowatt hour (kWh)

— 1,000 thousand watts acting over a period of 1 hour. The kWh is a unit of energy. 1 kWh=3600 kJ.

ramp

— A change in generation output.

plug-and-play PV system

— A commercial, off-the-shelf photovoltaic system that is fully inclusive with little need for individual customization. The system can be installed without special training and using few tools. The homeowner plugs the system into a PV-ready circuit and an automatic PV discovery process initiates communication between the system and the utility. The system and grid are automatically configured for optimal operation.

electrolyte

— A nonmetallic (liquid or solid) conductor that carries current by the movement of ions (instead of electrons) with the liberation of matter at the electrodes of an electrochemical

pulse-width-modulated (PWM) wave inverter

— A type of power inverter that produce a high quality (nearly sinusoidal) voltage, at minimum current harmonics.

volt (V)

— A unit of electrical force equal to that amount of electromotive force that will cause a steady current of one ampere to flow through a resistance of one ohm.

power conditioning equipment

— Electrical equipment, or power electronics, used to convert power from a photovoltaic array into a form suitable for subsequent use. A collective term for inverter, converter, battery charge regulator, and blocking diode

overcharge

— Forcing current into a fully charged battery. The battery will be damaged if overcharged for a long period.

solar-grade silicon

— Intermediate-grade silicon used in the manufacture of solar cells. Less expensive than electronic-grade silicon.

power factor (PF)

— The ratio of actual power being used in a circuit, expressed in watts orkilowatts, to the power that is apparently being drawn from a power source, expressed in volt-amperes or kilovolt-amperes. The ratio of real power (watts) to apparent power (volt-amps) in an AC circuit. Displacement power factor is the ratio of fundamental watts to fundamental RMS volts times.

solar spectrum

— The total distribution of electromagnetic radiation emanating from the sun. The different regions of the solar spectrum are described by their wavelength range. The visible region extends from about 390 to 780 nanometers (a nanometer is one billionth of one meter). About 99 percent of solar radiation is contained in a wavelength region from 300 nm (ultraviolet) to 3,000 nm (near-infrared). The combined radiation in the wavelength region from 280 nm to 4,000 nm is called the broadband, or total, solar radiation.

downtime

— Time when the photovoltaic system cannot provide power for the load. Usually expressed in hours per year or that percentage

zenith angle

— the angle between the direction of interest (of the sun, for example) and the zenith (directly overhead). the angle between vertical line and the line intersecting the sun. (90°- zenith).

ASP

Average selling price.

tray cable (TC)

may be used for interconnecting balance-of-systems.

Cycle

- the discharge and subsequent charge cycle of a battery.

solar cell

A devise that changes solar energy into electrical energy

grid-interactive system

Same as grid-connected system.

Tedlar

The fairly rigid back material on a PV module, used to provide structural support for the cells.

power conversion efficiency

The ratio of output power to input power of the inverter.

Joule (J)

Unit of energy 1 J = 1/3600 kWh

DVM

digital Volt-meter.

Incident radition

solar radiation incident on solar cell or module.

CELL (battery)

A single unit of an electrochemical device capable of producing direct voltage by converting chemical energy into electrical energy. A battery usually consists of several cells electrically connected together to produce higher voltages. (Sometimes the terms cell and battery are used interchangeably).

ampere hour meter

An instrument that monitors current with time. The indication is the product of current (in amperes) and time (in hours).

BIPV

Building Integrated Photovoltaics; A term for the design and integration of PV into the building envelope, typically replacing conventional building materials. This integration may be in vertical facades, replacing view glass, spandrel glass, or other facade material; into semitransparent skylight systems; into roofing systems, into shading "eyebrows" over windows; or other building envelope systems

Charge Controller

Device that manages the charge and discharge of batteries from a photovoltaic array. It ensures that batteries are not over charged or over discharged to make the batteries last longer

Bulk semiconductor material

Either the p-type or the n-type region of a solar cell - the thicker part. e.g. p-type semiconductor bulk material might be doped with an n-type dopant to form a thin n-type layer on one surface

Breakdown voltage

Minimum reverse voltage to make the diode conduct in reverse

British thermal unit (Btu)

The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit; equal to 252 calories.

Availability

The quality or condition of a photovoltaic system available to provide power to a load. Usually measured in hours per year. One minus availability equals downtime.

Amp hour

The quantity of electrical energy corresponding to the flow of current of one ampere for one hour. The term is used to quantify the energy stored in a battery. Most batteries are rated in Ah.

CFL - COMPACT FLUORESCENT LAMP

a light bulb that is utilized in an incandescent fixture, and has the efficiency and qualities of a standard fluorescent bulb. These bulbs generally offer 75% savings in electricity while maintaining comparable light levels.

Amorphous semiconductor

a non-crystalline semiconductor material manufactured by depositing layers of doped silicon on a substrate. Easier and cheaper to make than crystalline, but less efficient and slowly degrades over time. Also called thin film.

photovoltaics

generating electricity from the sun, made of silicon, solar panel, can get a refund for excess electricity generated/can store excess

Balance of System costs

in a photovoltaic system the balance of system (bos) costs are made up of the costs of all components except those of the modules. bos costs comprise planning costs, construc- tion preparation costs, the mounting system, dC cabling, inverters, buildings, grid connection and installation.

Amorphous modules

modules made of amorphous silicon (a-si) are a type of thin- film modules. their cells are made up of glass or metal panes coated with a thin layer of silicon. the name comes from the fact that, when the glass or metal is coated, the silicon atoms are not distributed in the crystalline structure but are spread amorphously, i.e. at random. a-si modules can be recognised by their brown colour.

Ampere hour (Ah)

the quantity of electrical energy equal to the flow of current of one ampere for one hour.

external quantum efficiency (external QE or EQE)

Quantum efficiency that includes the effect of optical losses, such as transmission through the cell and reflection of light away from the cell.

direct beam radiation

Radiation received by direct solar rays. Measured by a pyrheliometer with a solar aperture of 5.7° to transcribe the solar disc.

Diffuse Radiation:

Radiation received from the sun after reflection and scattering by the atmosphere and ground.

rated power

Rated power of the inverter. However, some units can not produce rated power continuously. the sine of the phase angle between the current and voltage waveforms in an AC system

Energy Contribution Potential

Recombination occurring in the emitter region of a photovoltaic cell.

flat-plate PV

Refers to a PV array or module that consists of nonconcentrating elements. Flat-plate arrays and modules use direct and diffuse sunlight, but if the array is fixed in position, some portion of the direct sunlight is lost because of oblique sun-angles in relation to the array.

Electrochemical

Refers to chemical reactions where electricity is either consumed or released in the process. Chemical reactions are ones where chemical bonds are broken and reformed

LOAD2

Refers to equipment that is powered by electricity. Usually expressed in terms of amperes or watts. In an electrical circuit, any devise or appliance that uses power (such as a light bulb or water pump).

Renewable energies

Renewable energies (also known as regenerative energies) are defined as energies from a source which either renews itself in the short term or where use does not contribute to exhausting the respective source. this includes solar irradia- tion and hydropower, geothermics and the potential in the energy recoverable from tidal power or biomass. the share of renewable energy sources in Germany's energy consump- tion is now higher than 17 percent. the use of solar power through photovoltaics has recorded the highest growth rates in renewable energies for a number of years.

Shunt resistance

Resistance which causes power loss, and typically caused by manufacturing defects. Shunts provide a conduction path that bypasses the p-n junction in a solar cell.

Series resistance

Resistance which is caused by the movement of current through the emitter and base of the solar cell; the contact resistance between the metal contact and the silicon; and finally the resistance of the top and rear metal contacts. Parasitic resistance to current flow in a cell due to mechanisms such as resistance from the bulk of the semiconductor material, metallic contacts, and interconnections.

depletion zone

Same as cell barrier. The term derives from the fact that this microscopically thin region is depleted of charge carriers (free electrons and hole).

Off-grid

See stand-alone.

Crystalline modules

Crystalline modules are made of solar cells with crystalline silicon which is around 0.2 to 0.4 millimetres thick. a dif- ferentiation is made between modules with monocrystalline and polycrystalline (also known as multicrystalline) cells. the basic material is ultra-pure polysilicon. efficiency is be- tween 14 and 18 percent.

majority carrier

Current carriers (either free electrons or holes) that are in excess in a specific layer of a semiconductor material (electrons in the n-layer, holes in the p-layer) of acell.

Reverse Leakage Current

Current flowing from that semiconductor device when the device is reverse biased (connecting the p-type silicon to negative terminal, and n-type silicon to the positive terminal

PHOTOVOLTAICS (PV):

Photo = light; Volt = electric al potential — Literally: electricity from light. Einstein won the Nobel Prize for discovering that when light shines on certain materials (like silicon), an electrical current is generated. field of technology and research related to the application of solar cells for energy by converting solar energy (sunlight, including ultra violet radiation) directly into electricity. Photovoltaics are best known as a method for generating electric power by using solar cells to convert energy from the sun into electricity. The photovoltaic effect refers to photons of light knocking electrons into a higher state of energy to create electricity. The term photovoltaic denotes the unbiased operating mode of a photodiode in which current through the device is entirely due to the transduced light energy. Virtually all photovoltaic devices are some type of photodiode. Solar cells produce direct current electricity from light, which can be used to power equipment or to recharge a battery. The first practical application of photovoltaics was to power orbiting satellites and other spacecraft, but today the majority of photovoltaic modules are used for grid connected power generation. Due to the growing demand for clean sources of energy, the manufacture of solar cells and photovoltaic arrays has expanded dramatically in recent years. Photovoltaic production has been doubling every 2 years, increasing by an average of 48 percent each year since 2002, making it the world's fastest-growing energy technology.

Co savings

Photovoltaic plants make a contribution to climate protec- tion: an example is the 15.8 megawatt solar power plant in moos near würzburg (Germany) which saves around 9.700 tonnes of carbon dioxide (Co ) a year.

load forecast

Predictions of future demand. For normal operations, daily and weekly forecasts of the hour-by-hour demand are used to help develop generation schedules to ensure that sufficient quantities and types of generation are available when needed.

REGULATOR

Prevents overcharging of batteries by controlling charge cycle-usually adjustable to conform to specific battery needs. Similar to a charge controller but usually has additional capabilities to control systems components other than batteries (e.g. a diesel generator or PV array).

PHOTOVOLTAIC (PV) CELLS

The smallest semiconductor element within a PV module to perform the immediate conversion of light into electrical energy (direct current voltage andcurrent). Also called a solar cell. made of semiconducting materials that can convert incident radiation in the solar spectrum to electric currents; PV cells are most commonly made of silicon, and come in two varieties, crystalline and thin-film type. When a photon is absorbed by a semiconducting material, it increases the energy of a valence band electron, thrusting it into the conduction band (when the energy of incident photons is higher than the bandgap energy); the conducting band electron then produces a current that moves through the semiconducting material. The materials used in PV cells have different spectral responses to incident light, and exhibit a varying sensitivity with respect to the absorption of photons at given wavelengths. Each semiconductor material will have an incident radiation threshold frequency, below which no electrons will be subjected to the photovoltaic effect. Above the threshold frequency, the kinetic energy of the emitted photoelectron varies according to the wavelength of the incident radiation, but has no relation to the light intensity. Increasing light intensity will proportionally increase the rate of photoelectron emission in the photovoltaic material. In actual applications, the light absorbed by a solar cell will be a combination of direct solar radiation, as well as diffuse light bounced off of surrounding surfaces. Solar cells are usually coated with anti-reflective material so that they absorb the maximum amount of radiation possible.

CELL (solar)

The smallest, basic Photovoltaic device that generates electricity when exposed to light. A device that produces electricity from light. Cells are the building block for modules.

Insolation

The solar radiation incident on an area over time. Equivalent to energy and usually expressed in kilowatt-hours per square meter. 2 (Incident Solar Radiation): measurement of solar radiation energy (all wavelengths) received on a given surface area in a given time. The basic unit of measurement is the Langley (a unit of heat energy equivalent to 1 calorie falling on 1cm2 of surface).

root mean square (RMS)

The square root of the average square of the instantaneous values of an ac output. For a sine wave the RMS value is 0.707 times the peak value. The equivalent value of alternating current, I, that will produce the same heating in a conductorwith resistance, R, as a dc current of value I.

solar constant

The strength of sunlight; 1353 watts per square meter in space and about 1000 watts per square meter at sea level at the equator at solar noon. It increases at higher altitudes.

Staebler-Wronski effect

The tendency of the sunlight to electricity conversion efficiency ofamorphous silicon photovoltaic devices to degrade (drop) upon initial exposure to light.

Rated Battery Capacity

The term used by battery manufacturers to indicate the maximum amount of energy that can be withdrawn from a battery under specified discharge rate and temperature. See battery capacity.

Solar Noon

The time of the day, at a specific location, when the sun reaches its highest, apparent point in the sky; equal to true or due geographic south.

photovoltaic (PV) generator

The total of all PV strings of a PV power supply system, which are electrically interconnected.

PHOTOVOLTAIC (PV) PANEL I MODULE

a packaged interconnected assembly of photovoltaic cells (solar cells -usually made from a monocrystalline silicon wafer). PV cells can be arranged in a series configuration to form a module, and modules can then be connected in parallel-series configurations to form arrays. When connecting cells or modules in series, they must have the same current rating to produce an additive voltage output, and similarly, modules must have the same voltage rating when connected in parallel to produce larger currents. A collection of PV panels are mechanically fastened together, wired, and designed to be a field- installable unit, sometimes with a glass covering and a frame and backing made of metal, plastic or fibreglass. A photovoltaic installation typically includes an array of PV panels, an inverter, batteries and interconnection wiring. The average daily electric power output of a solar photovoltaic system is approximately equal to its power output multiplied by the average peak hours of sunlight (roughly around 4-5 hours/day, or 40-50% of direct sunlight hours). Watt-peak (Wp) is the amount of power that a PV module is able to supply when it receives 1000 W/m2 of solar irradiance. A barrel of oil (159 I) produces 1700 KWH, at $80/barrel (Sep.2010): $0.05/kWh [1m3 of gas generates 10.59 kWh, at $0.29/m3: 0.03 kWh]; however, this is only the energy generation cost; capital equipment costs (power plant) are not taken into account, neither the transmission losses from the central power plant to the consumer.

Shockley-Read-Hall Recombination

a process in which an electron (or hole) is trapped by an energy state in the forbidden region which is introduced through defects in the crystal lattice. These defects can either be unintentionally introduced or deliberately added to the material, for example in doping the material and if a hole (or an electron) moves up to the same energy state before the electron is thermally re-emitted into the conduction band, then it recombines.

Radiative Recombination

a process in which an electron from the conduction band directly combines with a hole in the valence band and releases a photon.

LED - Light Emitting Diode

a semiconductor diode which glows when a voltage is applied. The LED was first invented by Oleg Vladimirovich Losev (Russia); in the 1920s. All early devices emitted low-intensity red light, but modern LEDs are available across the visible, ultraviolet and infra red wavelengths, with very high brightness.

Schottky diode

a special diode with a very low voltage drop, usually in the .15 to .25 volt range. Often used as blocking diodes in solar panels and arrays to minimize power loss. A normal silicon diode drops at least .7 volts

HYBRID SOLAR SYSTEM

a system that combines different energy sources. Many hybrid systems are stand-alone systems, which operate "off-grid"—not connected to an electricity distribution system. For the times when neither the wind nor the solar system are producing, most hybrid systems provide power through batteries and/or an engine generator powered by conventional fuels, such as diesel.

Busbar

a thin strip of copper or aluminum between cells that conducts electricity.

HOLE

a vacant position in a crystal lattice left by the absence of an electron, especially a position in a semiconductor (like a solar cell) that acts as a carrier of positive electric charge

INVERTER

converts the DC-direct current (12v, 24v, 36v) in a battery to 110-240V AC-alternating current; it is made to change the direct current (DC) electricity from a photovoltaic array into alternating current (AC) for use with electrical appliances or a utility grid. The conversion of DC to AC power results in an energy loss of approximately 10% for a solar energy system. Inverters come in two basic output designs, pure sine wave and modified sine wave (square wave). Most AC devices work fine on the modified sine wave inverter, but there are some exceptions (motors and power supplies usually run warmer and less efficiently). However, modified sine wave inverters make the conversion from DC to AC very efficiently, and they are relatively inexpensive. Pure sine wave inverters provide AC power that is virtually identical to, and often cleaner than, power from the grid. Inverters are generally rated by the amount of AC power they can supply continuously. Manufacturers generally also provide 5 second and 1/2 hour surge figures. The surge figures give an idea of how much power can be supplied by the inverter for 5 seconds and 1/2 an hour before the inverter's overload protection trips and cuts the power.

TFPV - THIN-FILM PHOTOVOLTAICS

photovoltaic modules constructed with sequential layers of thin film semiconductor materials only micrometers thick deposited onto glass substrate. Materials such as amorphous silicon (a-Si) or polycrystalline materials (cadmium telluride (CdTe) and copper indium (gallium) diselenide -CIS, CIGS), a few microns or less in thickness, are used to make photovoltaic cells. Thin-film cells are flexible and can be placed between flexible laminate, steel or glass, and take up a lot less space than a traditional panels. TFPV panels (or modules) are incorporated into the building envelope substituting cladding materials (ceramics, tiles, or marble, granite, glass or aluminium panels) with glass laminates that encapsulate photovoltaic cells. The modules are placed on top of raw building materials (brick, concrete), on the building roof or fagade. The main advantage of a-Si in large scale production is not efficiency, but cost; a-Si cells use approximately 1% of the silicon needed for typical c-Si cells (the cost of the silicon is by far the largest factor in cell cost). TFPV modules have an energy conversion rate of around 12% (a module of 12% efficiency with a 1 m2 surface area can be expected to produce approximately 120 watts of power). Monocrystalline and polycrystalline cells work well in bright cool conditions, whereas thin-film (amorphous) silicon cells are more efficient at higher temperatures.

Conduction Band

quantifies the range of energy required to free an electron from its bond to an atom.

SOLAR RADIATION

radiant energy emitted by the sun from a nuclear fusion reaction that creates electromagnetic energy. It is the dominant energy input to the Earth and is intercepted by the atmosphere and absorbed at the surface (watts/m2). The spectrum of solar radiation is close to that of a black body with a temperature of about 5800 K. About half of the radiation is in the visible short-wave part of the electromagnetic spectrum; the other half is mostly in the near-infrared part, with some in the ultraviolet part of the spectrum. Direct normal solar radiation refers to the sunlight that can cast a shadow. A certain percentage of solar radiation is made up of diffuse or scattered light, caused by clouds, humidity or particulates. Solar resource measurements are reported as either direct normal radiation (no diffuse light) or total radiation (direct+diffuse). At the sunward surface of a photovoltaic cell the average incident irradiance radiation is about 1000 W/m2.

Direct radiation

radiation received by direct solar rays. Measured by a pyrheliometer with a solar aperture of 5.7° to transcribe the solar disc. Sometimes also expressed as "beam radition".

I-V (current-voltage) CURVE

shows the possible combinations of current and voltage output of a photovoltaic device. A solar module produces its maximum current when there is no resistance in the circuit, i.e., when there is a short circuit between its positive and negative terminals (short circuit current), and the voltage in the circuit is zero. The maximum voltage occurs when there is a break in the circuit (Open circuit Voltage -Voc); under this condition the resistance is infinitely high and there is no current. These two extremes in load resistance, and the whole range of conditions in between them, are depicted on the l-V curve. Current, in amps, is on the vertical axis; Voltage, in volts, is on the horizontal axis. The power available from a photovoltaic device at any point along the curve is just the product of current and voltage at that point and is expressed in watts. Both at the short circuit current point (zero voltage) and at the open circuit voltage point (zero current) the power output is zero. There is a point on the knee of the curve where the maximum power output is located. The l-V of a PV device curve is based on the device being under standard conditions of sunlight and device temperature (no shading on the device): kW/m2 (one sun or a peak sun). PV cells can be modeled as a current source in parallel with a diode; when there is no light present to generate any current, the PV cell behaves like a diode. As the intensity of incident light increases, current is generated by the PV cell. In an ideal cell, the total current I is equal to the current lf generated by the photoelectric effect minus the diode current lD. The l-V curve of an illuminated PV cell has the shape shown in figure as the voltage across the measuring load is swept from zero to Voc, and many performance parameters for the cell can be determined from this data. For a module or array of PV cells, the shape of the l-V curve does not change. However, it is scaled based on the number of cells connected in series and in parallel.

Degradation

solar cells age as, over the course of their lifetime, their ef- ficiency diminishes. this natural process of ageing induced by light irradiation is called degradation. in calculating yield assumptions this effect is generally already included.

Solar silicon

solar silicon (also known as polysilicon) is the basic mate- rial used in the production of crystalline solar modules. the production of solar cells necessitates silicon in an ultra-pure form (solar grade).

APPROPRIATE TECHNOLOGY

technology, processes, products and services whose nature corresponds to the environment, the socio-cultural milieu and the needs of broad sectors of the population. array acts like a central generating plant, supplying power to the grid.

CRI - COLOUR RENDERING INDEX:

the ability of a light source to produce colour in objects. The CRI is expressed on a scale of 0-100, where 100 is the best in producing vibrant colour

TRANSMITTANCE

the amount of solar energy (visible, infrared and ultraviolet) that passes through a glazing system, expressed as a percent.

balance of system

(BOS)--Represents all components and costs other than the PV modules. It includes design costs, land, site preparation, system installation, support structures, power conditioning, operation and maintenance costs, batteries, indirect storage, and related costs.

a-Si - AMORPHOUS SILICON

(or a-Si) is the non-crystalline allotropic form of silicon. It can be deposited in thin films at low temperatures onto a variety of substrates, which offers some unique capabilities in a variety of electronics. It is the most well developed of the thin film technologies. In its simplest form, the cell structure has a single sequence of p-i-n layers. Such cells suffer from significant degradation in their power output (in the range 15-35%) when exposed to the sun. The mechanism of degradation is called the Staebler-Wronski Effect, after its discoverers. Better stability requires the use of a thinner layers in order to increase the electric field strength across the material. However, this reduces light absorption and hence cell efficiency. In manufacturing Amorphous Solar Cells techniques such as the condensation of gaseous silicon are used to make cells with a thickness that can be measured in the number of atomic layers. The atoms in such thin films of silicon are arranged in a completely random fashion and the cell is called an amorphous thin-film cell. Though these cells are inexpensive, average efficiencies are around 5 to 15%.

Cathodic protection

- a method of preventing oxidation (rusting) of exposed metal structures, such as bridges and pipelines, by imposing between the structure and the ground a small electrical voltage

Battery capacity

- the total number of ampere-hours that can be withdrawn from a fully charged battery at a specified discharge rate and temperature.

air mass (sometimes called air mass ratio)

. Equal to the cosine of the zenith angle-that angle from directly overhead to a line intersecting the sun. The air mass is an indication of the length of the path solar radiation travels through the atmosphere. An air mass of 1.0 means the sun is directly overhead and the radiation travels through one atmosphere (thickness). 2 length of a pat through the earth's atmosphere traversed by the direct solar beam, expressed as a multiple of the path traversed to a point at sea level with the sun directly overhead. Air mass index is defined at standard barometric pressure. The reference spectrum for standard test conditions (STC) was defined to be AM1.5

Azimuth Angle

. The angle between true south and the point on the horizon directly below the sun. 2. Angle between the north direction and the projection of the surface normal into the horizontal plane; measured clockwise from north. As applied to the PV array, 180 degree azimuth means the array faces due south

Array

1. A number of Solar PV modules connected together electrically, to provide a single electrical output. (Also Solar PV panels). 2. PV cells can be arranged in a series configuration to form a module, and modules can then be connected in pa rail el-series configurations to form arrays. When connecting cells or modules in series, they must have the same current rating to produce an additive voltage output, and similarly, modules must have the same voltage rating when connected in parallel to produce larger currents.

angle of incidence

1. The angle that a ray of sun makes with a line perpendicular to the surface. For example, a surface that directly faces the sun has a solar angle of incidence of zero, but if the surface is parallel to the sun (for example, sunrise striking a horizontal rooftop), the angle of incidence is 90°. 2. Angle between the normal to a surface and the direction of incident radiation; applies to the aperture plane of a solar collector. Most modern solar panels have only minor reductions in power output within plus/minus 15 degrees. The loss is a function of the cosine, so at 45 degree angle, output drops off by about 30%.

Battery

1. a device that converts the chemical energy directly into electrical energy by means of an electrochemical reaction. - 2. Batteries are often sold with a solar electric system. The primary purpose is to store the electricity not immediately used, which could be used at some later time

Battery backup

A device which maintains a continuous supply of electric power to connected equipment by supplying power from a separate source when utility power is not available

Bypass Diode

A diode connected across one or more solar cells in a photovoltaic module such that the diode will conduct if the cell(s) become reverse biased. Alternatively, diode connected anti-parallel across a part of the solar cells of a PV module. It protects these solar cells from thermal destruction in case of total or partial shading of individual solar cells while other cells are exposed to full light. 2. a diode connected anti-parallel across a part of the solar cells of a PV module. It protects solar cells from destruction in case of total or partial shading of individual solar cells.

acceptor

A dopant material, such as boron, which has fewer outer shell electrons than required in an otherwise balanced crystal structure, providing a hole, which can accept a free electron.

antireflection coating

A thin coating of a material applied to a solar cell surface that reduces the light reflection and increases light transmission. Antireflective coatings minimise incident light reflection from the cell .For maximum efficiency all light incident on the cell should be trapped inside it.

Cell Barrier

A very thin region of static electric charge along the interface of the positive and negative layers in a photovoltaic cell. The barrier inhibits the movement of electrons from one layer to the other, so that higher‐energy electrons from one side diffuse preferentially through it in one direction, creating a current and thus a voltage across the cell. Also called depletion zone or space charge.

Cdte modules

Cdte modules are thin-film modules which use the semi- conductor material cadmium telluride to generate electric- ity. the cadmium content is low. heavy metal cannot be dis- solved through a non-technically procedure so there is no danger for the user or the environment

a-Si/µc-Si

Dual amorphous silicon / micro-crystalline silicon absorber (also referred to as tandem, micromorph). Micro and nano-crystalline are interchangeable.

baseline performance value

Initial values of Isc, Voc, Pmp, Imp measured by the accredited laboratory and corrected to Standard Test Conditions, used to validate the manufacturer's performance measurements provided with the qualification modules per IEEE 1262

band gap energy (Eg)

The amount of energy (in electron volts) required to free an outer shell electron from its orbit about the nucleus to a free state, and thus promote it from thevalence to the conduction level. In a semiconductor, the energy difference between the highest valence band and the lowest conduction band.

annual solar savings

The annual solar savings of a solar building is the energy savings attributable to a solar feature relative to the energy requirements of a non-solar building.

cell junction

The area of immediate contact between two layers (positive and negative) of aphotovoltaic cell. The junction lies at the center of the cell barrier or depletion zone.

Base Load

The average amount of electric power that a utility must supply in any period.

Average Demand

The energy demand for a given location over a period of time. For example, the number of kilowatt-hours used in a 24-hour period, divided by 24, tells the average demand for that location in that time period

Barrier Energy

The energy given up by an electron in penetrating the cell barrier; a measure of the electrostatic potential of the barrier.

cathode

The negative pole or electrode of an electrolytic cell, vacuum tube, etc., whereelectrons enter (current leaves) the system; the opposite of an anode.

battery life

The period during which a cell or battery is capable of operating above a specified capacity or efficiency performance level. Life may be measured in cycles and/or years, depending on the type of service for which the cell or battery is intended.

activated shelf life

The period of time, at a specified temperature, that a charged battery can be stored before its capacity falls to an unusable level.

Capacity Factor:

The ratio of the average load on (or power output of) an electricity generating unit or system to the capacity rating of the unit or system over a specified period of time.

Ambient Temperature:

The temperature of the surrounding area.

battery energy capacity

The total energy available, expressed in watt-hours (kilowatt-hours), which can be withdrawn from a fully charged cell or battery. The energy capacity of a given cell varies with temperature, rate, age, and cut-off voltage. This term is more common to system designers than it is to the battery industry where capacity usually refers toampere-hours

battery available capacity

The total maximum charge, expressed in ampere-hours, that can be withdrawn from a cell or battery under a specific set of operating conditions includingdischarge rate, temperature, initial state of charge, age, and cut-off voltage.

ampere (A) or amp

The unit for the electric current; the flow of electrons. One amp is 1 coulomb passing in one second. One amp is produced by an electric force of 1 volt acting across a resistance of 1 ohm. A unit of electrical current or rate of flow of electrons. One volt across one ohm of resistance causes a current flow of one ampere. One ampere is equal to 6.235 x 10 18 electrons per second passing a given point in a circuit.

array operating voltage

The voltage produced by a photovoltaic array when exposed to sunlight and connected to a load

Activation Voltage(s):

The voltage(s) at which a charge controller will take action to protect the batteries.

base load generating plants

Typically coal or nuclear generating units that are committed and dispatched at constant or near-constant levels with minimum cycling. They are often the sources of lowest-cost of energy when run at very high capacity factors

Auger Recombination

a process in which the excess energy given off by an electron recombining with a hole is given to a second electron (in either band) instead of just emitting the energy as a photon. The newly excited electron then gives up its additional energy in a series of collisions with the lattice, relaxing back to the edge of the band.

ACTIVE SOLAR SYSTEM:

a solar system that generate electricity or require a mechanical device (fans, pumps, motors powered by energy not derived from solar radiation) for collecting, storing and distributing thermal (heat) energy.

Accumulator

an accumulator stores electrical energy. in photovoltaics, ac- cumulators are used for stand-alone systems.

Amortisation

energetic amortisation (also known as energy return time) is the time which a solar electricity system needs to generate the energy used for its production and installation. when the period of its energetic amortisation has expired, its balance of energy is then positive. there is no energetic amortisation in the case of power plants operated with fossil fuels

BAPV - BUILDING APPLIED PHOTO VOLT AICS

it's a retrofit added to the building after construction. The photovoltaics is not part of the design of the building skin and roof. BAPV modules have an energy conversion rate of around 11% (a module of 11% efficiency with a 1 m2 surface area can be expected to produce approximately 110 watts of power).

AMPERAGE:

the amount of electrical current through a conductive source, Ampere (A) is the unit of electric current: the rate of flow of electrons in a conductor equal to one coulomb per second

CELL EFFICIENCY

the percentage of electrical energy that a solar cell produces (under optimal conditions) as compared to the total amount of energy from the sun falling on the cell. At the sunward surface of the cell the highest possible average incident solar radiation is about 1000 W/m2