PV Systems Chp 5 & 6

monopole array

A PV array that has one positive terminal and one negative terminal.

bipolar array

A PV array that has two terminals, one positive, and one negative, and a third terminal connected at a center tap.

module

A PV device consisting of a number of individual cells connected electrically, laminated, encapsulated, and packaged into a frame. (Important Term)

cycle

A battery discharge followed by a charge.

secondary battery

A battery that can store and deliver electrical energy and can be charged by passing a current through it in an opposite direction to the discharge current.

primary battery

A battery that can store and deliver electrical energy but cannot be recharged.

hybrid battery

A battery that uses a combination of plate designs to maximize the desirable characteristics of each.

CRC

A catalytic recombination cap is a vent cap that reduces electrolyte loss from an open-vent flooded battery by recombining vented gases into water.

multijunction cell

A cell that maximizes efficiency by using layers of individual cells that each respond to different wavelengths of solar energy. (Important Term)

photoelectrochemical cell

A cell that relies on chemical processes to produce electricity from light, rather than using semiconductors.

stationary battery

A class of battery designed for occasional deep-discharge limited-cycle service.

traction battery

A class of battery designed for repeated deep-discharge cycle service.

battery

A collection of electrochemical cells that are contained in the same case and connected together electrically to produce a desired voltage.

array

A complete PV power-generating unit consisting of a number of individual electrically and mechanically integrated modules with structural supports, trackers, or other components. (Important Term)

stratification

A condition of flooded lead-acid cells in which the specific gravity of the electrolyte is greater at the bottom than at the top.

series

A connection of PV modules by connecting conductors between the positive terminal of one module to the negative terminal of the next module. The voltage output of the entire string of modules is the sum of the voltages of the individual devices. Only PV modules having the same current output should be connected this way. (Important Term)

parallel

A connection of series strings of PV modules by connecting the positive terminals of each series string together and all the negative terminals together at common terminals or busbars. The overall circuit current is the sum of the current from the individual strings. The overall circuit voltage is the same as the voltage of individual strings. Only series strings of similar voltage output should be connected this way. (Important Term)

bypass diode

A diode used to pass current around, rather than through, a group of PV cells.

family of I-V curves

A group of I-V curves for a particular PV device at various operating conditions.

battery bank

A group of batteries connected together with series and/or parallel connections to provide a specific voltage and capacity.

semiconductor

A material that can exhibit properties of both an insulator and a conductor.

grid

A metal framework that supports the active material of a battery cell and conducts electricity.

thin-film module

A module-level PV device with its entire substrate coated in thin layers of semiconductor material using chemical vapor deposition techniques, and then laser-scribed to delineate individual cells and make electrical connections between cells.

PV cell

A semiconductor device that converts solar radiation into direct current electricity. (Important Term)

p-type

A semiconductor that has electron voids (holes).

n-type

A semiconductor that has free electrons.

ribbon wafer

A silicon wafer made by drawing a thin strip from a molten silicon mixture.

polycrystalline wafer

A silicon wafer made from a cast silicon ingot that is composed of many silicon crystals.

monocrystalline wafer

A silicon wafer made from a single silicon crystal grown in the form of a cylindrical ingot.

SLI

A starting, lighting, and ignition battery is a class of battery designed primarily for shallow-discharge cycle service.

string

A subset of a PV array consisting of modules electrically connected in series. (Important Term)

catalyst

A substance that causes other substances to chemically react but does not itself participate in the reaction.

wafer

A thin, flat disk or rectangle of base semiconductor material.

photon

A unit of electromagnetic radiation. (Important Term)

subarray

An electrical subset of a PV array.

plate

An electrode consisting of active material supported by a grid framework.

terminal

An external electrical connection point of a battery.

float charging

Battery charging at a low charge rate that finishes a charge and maintains full battery charge by counteracting self-discharge.

bulk charging

Battery charging at a relatively high charge rate that charges the battery up to a regulation voltage, resulting in a state of charge of about 80% to 90%.

absorption charging

Battery charging following bulk charging that reduces the charge current to maintain the battery voltage at a regulation voltage for a certain period. (Important Term)

equalization charging

Current-limited battery charging for a limited time period to a voltage higher than the normal bulk charging voltage in order to bring each cell to a full state of charge. (Important Term)

DOD

Depth of Discharge, the percentage of energy withdrawn from a battery compared to the fully charged capacity. (Important Term)

flooded electrolyte

Electrolyte in the form of a liquid.

captive electrolyte

Electrolyte that is immobilized.

PTC

PVUSA Test Conditions, a set of solar module reference conditions that rates module performance at a solar irradiance of 1000 W/m², ambient temperature of 20°C (68°F), and wind speed of 1 m/s. (Important Term)

panel

Sometimes this term is used as an alternate term for a PV module. More commonly, the term panel refers to an assembly of two or more modules that are mechanically and electrically integrated into a unit to ease of installation in the field. (Important Term)

STC

Standard Test Conditions, the most common and internationally accepted set of reference conditions for solar modules. Rates module performance at solar irradiance of 1000 W/m², spectral conditions of AM 1.5, and a cell temperature of 25°C (77°F). (Important Term)

SOC

State of Charge, the percentage of energy remaining in a battery compared to its fully charged capacity. (Important Term)

autonomy

The amount of time a fully charged battery system can supply power to system loads without further charging.

average daily depth of discharge

The average percentage of the total capacity that is withdrawn from a battery each day.

I-V characteristic

The basic electrical output profile of a PV device.

cell

The basic unit in a battery that stores electrical energy in chemical bonds and delivers this energy through chemical reactions.

p-n junction

The boundary of adjacent layers of p-type and n-type semiconductor materials in contact with one another.

active material

The chemically reactive compound on a battery cell plate.

temperature-rise coefficient

The coefficient for estimating the rise in cell temperature above ambient temperature.

reverse bias

The condition of a PV device operating at a negative (reverse) voltage.

electrolyte

The conducting medium that allows the transfer of ions between battery cell plates. (Important Term)

gassing

The decomposition of water into hydrogen and oxygen gases as a battery charges.

current

The flow of charge resulting from the application of a difference in potential between two points in an electrical system. (Important Term)

self discharge

The gradual reduction in the state of charge of a battery while at steady-state condition. (Important Term)

I-V curve

The graphic representation of all possible voltages and current operating points for a PV device at a specific operating condition. (Important Term)

sulfation

The growth of lead sulfate crystals on the positive plate of a lead-acid cell. (Important Term)

Isc

The maximum current on an I-V curve and is the operating point for a PV device under no load or short-circuit condition, and no voltage output.

allowable depth of discharge

The maximum percentage of total capacity that is permitted to be withdrawn from a battery.

Imp

The maximum power current is the operating current on an I-V curve where the power output is at maximum.

Pmp

The maximum power point is the operating point on an I-V curve where the product of current and voltage is at maximum.

Vmp

The maximum power voltage is the operating voltage on an I-V curve where the product of current and voltage is at maximum.

capacity

The measure of the electrical energy storage potential of a cell or battery.

cutoff voltage

The minimum battery voltage specified by the manufacturer that establishes the battery capacity at a specific discharge rate.

breakdown voltage

The minimum reverse-bias that results in a rapid increase in current through an electronic device.

photovoltaic effect

The movement of electrons within a material when it absorbs photons with energy above a certain level.

Voc

The open-circuit voltage is the maximum voltage on an I-V curve and is the operating point for a PV device under infinite load or open-circuit condition, and no current output.

discharging

The process of a cell or battery converting chemical energy to electrical energy and delivering current.

charging

The process of a cell or battery receiving current and converting the electrical energy into chemical energy.

doping

The process of adding small amounts of impurity elements to semiconductors to alter their electrical properties.

temperature coefficient

The rate of change in voltage, current, or power output from a PV device due to changing cell temperature.

overcharge

The ratio of applied charge to the resulting increase in battery charge.

Fill factor

The ratio of maximum power to the product of the open-circuit voltage and short-circuit current. (Important Term)

charge rate

The ratio of nominal battery capacity to the charge time in hours.

discharge rate

The ratio of nominal battery capacity to the discharge time in hours.

efficiency

The ratio of power output to power input.

specific gravity

The ratio of the density of a substance to the density of water. (Important Term)

voltage

The term applied to the difference in electric potential between two points as established by a separation of opposite charges. (Important Term)

open-circuit voltage

The voltage of a battery or cell when it is at steady-state.

steady-state

an open-circuit condition where essentially no electrical or chemical changes are occurring.