Renewable Energy System Midterm 2

Which of the following statistics is true about US wind power as compared to other countries?

Rank #2 in the world in cumulative capacity installed

The primary purpose of thermal mass in a passive solar space heating application is to:

Reduce daily temperature swings by absorbing solar energy during the day and releasing it at night

Active/Indirect domestic hot water with glazed flat plate collector

colder climates, back up heat source

Based on the information calculated in the last 2 questions, what collector type would best suit this application?

either glazed-plate or evacuated tube

Wave energy machine needs three basic things in it's design, a moving part that follows the shape of the wave, a mechanical device/generator to convert the motion to electricity, and a ______

fixed frame of reference such as attachment to the ocean floor or a large stabilized body that doesn't move with the waves

Hydro resources very site specific

flow duration curve: rainfall patterns, size of drainage area, hydrology of drainage area

Energy from tidal barrage: low head hydro

gates control water in and out of barrage creating elevation difference to drive turbine -out-flow, in-flow, or both

Basic passive collector types: conservatory or atrium

glazed space attached on outside of building, can be added easily to existing buildings -can be used to pre-heat ventilation air -provide thermal buffer reducing heat losses through wall -minimal controls -need to control overheating in summer

Public perception of hydro power

good for environment, no pollution, cleaner, renewable natural water always available. Cost efficient -Disadvantages: damaging to fish, blocks migration, damaging to environmental, wildlife, lack of water, rain

While larger turbine blades can extract more energy from the wind resource, what is a typical downside to consider (select the best answer)?

greater propensity for high-speed wind damage

Which of these is a common strategy for placement of windows when considering passive solar approaches for building design in the US?

large south-facing windows, and small north-facing ones

1000.0 gpm (gallons-per-minute) of water is released from the reservoir down the hill in order to generate electricity during the day (peak hours) for a 12-hour period each day. The drop of the water is 50.0 m and has negligible friction. Calculate how much energy (in kWh/day) can be generated on a daily basis, if the turbine is 85% efficient. Assume the density of the water is 1000.0 kg/m3.

power= mass/time * gravity * height 1000 gallons/minute * 3.79 kg/ 1 gallon * 1 minute/60 sec = 63.167 kg/sec 63.167 kg/sec * 9.6 m/s2 * 50 m = 30951.83 W * 12 hrs= 371.412 kWh * 0.85= 315.71 kWh

Dam removal

reasons: improved fisheries, ecosystem restoration, pubic safety, financial savings (maintenance) -more being torn down than build right now

Small Hydro Systems ex

slovakia, canada, and usa -utility-owned, community-owned, independent power producer (IPP) -if grid-connected power purcahse agreement (PPA) helpful -run of river projects feed grid when flow available

Uses of hot groundwater- low temperature (below about 150C) geothermal sources

space heating, domestic hot water, greenhouses, aquaculture, crop drying, industrial processes

Wind farms generally have a favorable land-use intensity because

the area under the turbines can be used for agriculture/pasture

If over a year a refrigerator takes 250 kWh of electricity and can provide 4,500 MJ of cooling per year what is its COP? (Answer with at least 2 sig figs)

two ways: 1: 4,500 MJ * 1/250 kWh * 1 kwh/3.6MJ= 5 2: 4,500,000 kJ/ 250 kWh * 1 kWh/3600 kJ = 5

Types of heat pumps:

vertical- doesnt take as much land, horizontal, ponds-use water as heat exchange medium lower cost, heat sink of water source -earth tubes: if building air is blown through tubes instead of a heat exchange fluid, need to be much bigger

Global geothermal applications and potential

volcanic areas, tectonic boundaries -in US: Alaska, fault lines California and west, yellow-stone area

Pick the solar PV cell type with the highest conversion efficiency among the following (consider both those commercialized and those being developed)

multi-junction

Positives to wind power

no air pollution (particles, NOx, SOx, Hg), no carbon emissions, no water use, high energy ratio (output to input), efficient land use

Annual average solar energy (radiation) available to a collector at any point on the earth depends on...

angle of incidence (tilt and azimuth angle) of the collector, latitude (geometric considerations of the relationship between the earth and sun), weather patterns that influence cloud cover

CSP cost

becoming cost competitive, expected PV will grow faster due to economics -competitive cost, high coincidence with electric loads and predictability of supply have made large CSP projects popular

The electricity generation potential of a solar PV panel in the Phoenix area is 7.58 kWh/m2-day. Your client wants to install 20.0 m2 of mono-Si panels with an efficiency of 16.0%. An inverter, with an efficiency of 96.0% helps generate this energy as alternating current. How much electrical energy can she expect to generate in the first year of operation (answer to the nearest kWh)?

7.58 * 20 = 151.6 kWh/day * 365 days = 55334 kWh a year 55334 * .16 * .96 = 8500 kWh

A wind turbine is moved to a region where the wind speed is doubled. By what factor is the turbine's power output increased in the new location (assuming you are in the normal operating range of the turbine)?

8 Power increases cubed so if doubled then 2^3 is 8

Consider energy conversion in a parabolic trough concentrating solar power (CSP) system being installed in the Mojave Desert of Nevada, where the average direct normal solar resource is 8.30 (kWh)/(m2 day). This is the sunlight from the daylight hours over a day. The geometry of the parabolic trough creates a solar concentration factor of 90 to 1.0. -How much energy-per-unit area (in MWh/m2) is realized annually at the surface of the mirrors?

8.30 (kWh/m2 a day) x 365 days = 3029.5 kWh/m2= 3.03 mWh/m2

PV Materials: polymer

-Engineered semiconductor plastics -potential to future reduce cost -flexible and versatile -mid research stage

Basic passive collector types: Trombe Wall

-Glazing covering thin air space over absorber -may incorporate thermal storage in the wall- control over heat delivered to space over time

Wind velocity near a wind turbine doubles from 3 m/s to 6 m/s. (Assume that the wind turbine is able to operate and has the same conversion efficiency at both velocities.) Are the following statements about the wind energy in this situation true or false?

-Mass flow rate across the wind turbine increases by a factor of 2--> True -Kinetic energy per kg of air increases by a factor of 6--> False (factor of 4 since velocity is squared in energy equation) -Electrical power produced increases by a factor of 8--> True energy is cubed in power equation

Variation in time

-Monthly average wind speed, ex- Madison: late winter highest lowest wind speeds in fall -across a day (diurnal) higher in the middle of the day -daily wind patterns close to energy demand will have higher value

Positioning of solar collectors

-Orientation: general rule: collector should face equator (due south in northern hemisphere) Exception: to collect more radiation in the afternoon, collector may face slightly west (if less cloudy in afternoon, if heat losses from collector are important) -Tilt: general rule: angle between collector and ground should equal latitude. Exceptions: many, know this rule so you can break it

PV Materials: thin-film

-Thin consecutive layers of atoms or molecules -heat tolerant (good in concentrating PV) -resistant to radiation damage (good for space) -alloying with other materials can produce flexible array -early commercialization stage

Latitude and collector tilt

-Tilt angle= latitude for maximum total annual radiation -more vertical= more energy collected in winter (ex- space heating) -more horizontal= more energy collected in summer (ex- outdoor swimming pools) -a more horizontal position is better for summer, more vertical position is better in winter, a tile equal to latitude gives best performance in spring and autumn

Factors affecting wind shear

-Trees, buildings, rolling topography, hills -turbulence robs lots of energy from turbine -1/2 mile from tree groves -30 feet above mature tree height for small turbines -lowest surface roughness exponent: off-shore, highest: woodlands

Match the best application for the following solar collector types

-Unglazed flat-plate: swimming pool heating applications -glazed flat-plate air: crop drying applications -glazed flat-plat water: domestic water heating -evacuated tube: water, space and process heating, particularly in colder climates

Thermal mass

-absorbs and stores daytime solar energy released at night -evens out temperature swings: water drums, pebble beds, building materials (tile floors, masonry, etc)

Domestic hot water with evacuated tube collector

-active or passive designs, always indirect, well suited to cold climate applications -water/space/process heating

PV Materials: mutli-junction

-also called 'cascade' or 'tandem' cell, cells with different bandgaps are stacked on top of one another, much higher efficiencies possible than single junction cells

PV materials: Amorphous silicon

-atoms not regularly ordered, do not form crystal -have "dangling bonds" which allow electrons to recombine with holes -deterioration problems: 20% common before stabilizing -low cost, flexible

Tidal streams and currents

-barrage not needed: reduced cost (?), reduced environmental impact(?) -allow for energy production on both the ebbing and surging tides

Geopower benefits

-baseload: geothermal power plants produce electricity consistently, running 24 hours per day 7 days per week, regardless of weather conditions -small footprint: geothermal power plants are compact; on average using less land per GWh (404 m2) than most other renewables -GH: modern closed-loop geothermal power plants emit no greenhouse gasses -Water: geothermal power plants consume less water on average over the lifetime energy output than the most conventional generation technologies -Cost: one of the lowest LCOW for renewable

Day lighting

-beneficial to psychological well-being: studies show increases in learning, productivity -daylighting can pay off financially: electric lighting 40-60% of energy use in office buildings

Solar cooling

-building cooling loads are very well matched to solar availability -generate solar electricity (photovoltaic) to run an air conditioner -vapor compression cycle- heat pump

Short-term thermal storage: heat collected in the day is released at night

-building integrated thermal mass: heating floor, glazed flat plate or evacuated tube "water" collector -rock bed -water tank -phase change material

Building integrated solar collectors (windows)

-conservatory: atrium-solar energy preheats building ventilation air, normal air flow out through building leakage paths -trombe wall: solar radiation is absorbed and stored in the thermal mass behind the glazing -direct gain: solar radiation penetrates the windows and is absorbed by the normal building interior

Components of small hydro

-dam, barrage or weir: highly variable cost, high head developments tend to be less costly -Water handing: intake with trash rack, gate, values; tailrace at exit, excavated canal, underground tunnel and/or penstock -Power house: houses turbine, generator, power conditioning equipment

Small hydro project considerations

-development of time 2-5 years, environmental approvals and permits, resource surveys/hydraulic studies, feasibility study, system planning and engineering -keep costs down with simple civil structures -consider existing dam locations

Domestic hot water systems

-direct (open loop): potable water flows through collector, freezing can be a problem in cold climate -indirect (closed loop): heat transferred from antifreeze solution to potable water through heat exchanger, typically propylene glycol solution used as collector fluid -passive: no pumps needed to move collector fluid/water -active: collective fluid or water is moved through collector with a pump (that may be solar PV powered)

Which of the following are environmental risks of hydro power? (select all that apply)

-displaced people, flora and fauna in areas flooded for reservoirs -heating of water in the reservoir resulting in change cold-water ecosystems -emissions (methane and CO2) release from biomass decomposition in flooded reservoirs -erosion of steam bed downstream from the dam

Geothermal resources

-geo-erath; thermal-related to heat -geothermal is the energy resource related to heat of the earth -the earth's core is 11,000 degrees. That is hotter than the surface of the sun. It consists of molten iron -the earth's geothermal energy is created primarily by the decay of radioactive materials in the core and in the surrounding layers of rock -typically deeper= hotter -we cannot typically mine deep enough to get to the temperature to make steam -there are boundaries and faults are cracks in the Earth's crust where magma rises near or to the surface -geothermal plants take advantage of this fact using water heated by this volcanic activity to produce electric power

Ground source heat pumps

-geothermal heat pumps use the earth instead of air as the heat sink or source -used to provide heating, cooling, and hot water for your home -still requires energy source (electricity) to both move the heat and concentrate it

Two types of geothermal

-geothermal power: high temperature ground, used to make steam-> electricity, limited sites -geothermal heat pump: uses stable temperature near the surface, provide heating and cooling assistance, no electricity, generally done most places

History of Hydro Power

-global application as mechanical energy for water pumping, grain and wood milling -20,000 hydro plants in 1600s england

Heat Pump Cycle

-heat pumps "move" energy from one location to another, instead of creating heat by burning fossil fuels -uses vapor compression and pressure release to move heat from air

Performance comparisons (geothermal)

-heating performance ratings: geothermal (ground source) 3.5-6.0 COP, air source heat pump 1.8-2.0 COP, fossil fuel furnace 0.80-0.95 COP, electric furnace/baseboard/ceiling cable 1.00 COP -cooling performance ratings: geothermal 3.0-6.0 COP, air source heat pump 1.8-2.5 EER, air conditioner 3.0-5.0 EER -COP: ratio of useful heating or cooling provided to work requried

Types of wave power devices

-heaving, pitching, oscillating, and surging devices

hydropower environmental considerations

-impacts and environmental assessment requirements depend on site and type of project -run of river at existing dam: relatively minor -run of river at undeveloped site: dam/weir/diversion construction -water storage developments: larger impacts that increase with scale of project -warms cold water streams-change in fish habitat -bacteria and algae growth in reservoirs -CO2 release from reservoirs -social effects: displaces people when large reservoirs are flooded, site aesthetics, recreational/navigational uses -riverbed below Hoover dam lowered > 4 meters: changed irrigation potential -silt and gravel behind dam hurts fish spawning -coastal erosion at river mouth -controlled flooding to restore ecosystem is being implemented

Passive/Direct Domestic Hot Water

-integrated collector and (pressurized) storage tank -batch mode: direct heating of water during the day for use in evening or following morning -inexpensive -manage heat loss at night -vulnerable to freezing -well suited to warm climates

Total power in Wind

-kinetic energy of a mass of air moving at velocity V (0.5mV2) -energy (joules)/time(s)= power (watts) -mass of air going through the hoop per second ρAV ρ=air density 1.239 kg/m3 at standard conditions A=cross sectional area of the hoop (swept area of rotor) -power of a mass of air moving entering a HOOP at velocity V: 1/2ρAV3 V3: Wind velocity cubed

Window placement

-large south facing windows- maximize solar gain -small north facing windows- minimize heat loss

Medium head applications

-large volume water storage, dame and reservoir -dependable and controllable -often floods large land areas, mountain canyons -medium head Francis turbine: similar to Fourneyron except water flows through the middle, adjustable guide vanes to adjust for water flow rate, 90% + efficiency 10-20 meter head ex- hoover dam

Why do higher latitudes receive less solar radiation per area than lower latitudes?

-less concentrated radiation due to angle of incidence -more atmosphere to travel through

Match each type of hydroelectricity application with the concept that best describes it

-low head applications: use large volumes of water, which usually come from a river. It has the lowest elevation difference among hydro applications -Medium head applications: use large water volumes, which usually come from a reservoir (stored water) -High head applications: use small water reservoirs and large elevation differences to impulse a turbine for energy generations

PV materials: Polycrystalline silicon

-lower-grade silicon than monocrystalline -molten silicon poured into mold and allowed to solidify into ingot -lower operating efficient, but less expensive than monocrystalline

Glazed flat plate air collector

-medium temperature rise -mainly used for space heating -fans typically used to move air -rock bed or building-integrated thermal mass

Basic collector types: glazed flat plat (water)

-medium temperature rise: less heat loss than unglazed collector -selective coating of cover (glazing) usually engineered polymer -insulated at back -selective coating of absorber: domestic hot water, industrial process heat, space heating

Evacuated tubes

-medium/high temperature rise -vacuum tube prevents convective heat loss -highly engineered absorber -heat pipe in absorber carries heat to water -more expensive than flat-plate collectors

Tapered channel wave reservoir

-narrowing channel causes waves to increase height, spill over walls of the channel and into the reservoir, water than passes through hydroelectric turbines on the way back to sea level thus generating electricity

Solar environmental impacts:

-no emissions or noise -minimal land use or visual intrusion if stalled rooftops- land use may be substantial for large PV farms -some rare and toxic materials used in manufacture -battery impacts can be substantial-if used -compare with replaced/alternate energy source to judge relative impacts

PV applications opportunities and challenges

-on-grid, off-grid, improving technologies efficiency vs cost -de-carbonization of energy supply, global silicon shortage-competes with electronics industry

Swimming Pool application

-only used during warm seasons, spring/fall solar radiation in Madison about 700 W/m2 -temperature rise: air temp=15C, pool temp=24C, temp above ambient ambient 9C -temp rise/solar radiation= 9/700= 0.012 -unglazed plate most efficient and least expensive

Why is there potential for good off-shore wind resources? Select all answers that apply.

-open water typically has faster wind speeds, open water has a low wind-shear exponent, open water has less obstructions

Transpired plate unglazed air collector

-outside air enters through holes in dark metal absorber plate, then fan moves it into building -low temperature rise -low cost -typically used to pre-heat ventilation air for large buildings or for low temperature warehouses

Dish/Engine system

-parabolic dish focuses sunlight onto a receiver, which transfers heat to an engine -typically stirling engine used efficient, quiet, clean -concentration ratio: typically over 2000 -working temperatures: over 750 degrees C

Parabolic trough Concentrating Collector

-parabolic mirror concentrates sunlight on receiver tube- heat transfer fluid in tube usually oil, this fluid carries heat away from collector, generally using it to vaporize a secondary fluid to power a steam turbine -concentration ratio 30-100 suns -operating temperatures: 150-400 C -towers more popular now

What is true about how solar cells generate electricity? Select all that are true.

-photons hit the cell and dislodge electrons that flow and create a current -a single solar cell typically produces 1-2 W of power

Light pipes

-piped daylighting reflective light pipes fiber optics -selective lighting: light only work area -control system: automatically add backup lighting when daylight insufficient

Hydro Energy (powerxTime)

-potential energy= mgh -potential energy is converted into kinetic energy of falling water and then into electrical energy in a generator -conversion efficiency ~80-90% -friction losses in pipes, efficiency of converting waters kinetic energy into mechanical output energy of turbine, efficiency of converting turbined mechanical output energy into electrical energy in generator

one benefit of tidal power is that is

-produces predictable power and energy that can be easier to integrate into the grid

Fourth concept: we can calculate the mass flow rate going into the turbine by the cross sectional area, velocity, and the density

-thinking of a cylinder of fluid going into the turbine -mass flow rate= cross sectional area x velocity x density -[kg/s]=[m2]x[m/s]x[kg/m3]

Two types of tidal power

-tidal barrages: using the tides to create trap water behind a dam which is released to produce electricity similar to hydropower -tidal fences or turbines: using the kinetic energy of water current to produce power, like wind energy

Variation in daily energy output from a tidal power plant

-tides follow sinusoidal patterns -power generated in regular pattern -more predictable than wind or solar

Which of the followings are true about utility-scale concentrating solar therm power.

-water scarcity is a common challenge for CSP: true -The power supply is usually far from the demand geographically: true -it can use both direct and diffuse radiation: false -the efficiency is generally lower than common PV on the market: false

Wave power

-wave energy develop primarily by wind over water, amplified by land forms -transport of energy b wind waves, and the capture of that energy to do useful work -electricity generation water desalination or the pumping of water into reservoir -challenge to develop machines that can protect themselves from big waves

Is geothermal renewable?

-you are mining heat from the earth -vast but not unlimited supply -after heavy use for power generation would require time for regeneration -considered renewable: through proper reservoir management, the rate of energy extraction can be balances with a reservoir's natural heat recharge rate -Baseload- geothermal power plants produce electricity consistently running 24 hours per day 7 days a week regardless of weather conditions

Next, you'd like to estimate what sort of a collector would best serve your needs. Assume the irradiance during the winter months to be 350.0 W/m2. What is the temperature rise per incoming solar irradiance (W/m2) that needs to be attained for this scenario ? Answer in ∘C/(W/m2) with 2 significant figures.

0.11 (38/350)

You want to ensure the availability of hot water even in the dead of winter, and would like to now design the system for the coldest of days, an ambient temperature of -20.0 ∘C. Using this new temperature, but the same other conditions, recalculate the temperature rise per incoming solar irradiance that this will necessitate (in ∘C/(W/m2)).

0.19 (45--20)/350

The solar array is rated to produce 1.00 kW of power. The area where the PV system is installed has a capacity factor of 20.0%. What is the annual energy that this system can be expected to produce (in kWh, DC)?

1.00 kW x 8760 hours = 8760 kWh x .20% = 1752 kWh

If solar radiation in a concentrating solar power (CSP) is concentrated from 100 ft2 to 1 ft2, what is this device's concentration ratio (in suns)?

100

Your company just installed a 100.0 kW-rated wind turbine, located in an area with good wind resource, resulting in a capacity factor of 40%. You plan to sell this energy back to the grid at: $0.08/ kWh during peak hours, and $0.04/ kWh during off-peak hours. The peak hours are 8 hours per day.How much revenue can you expect to make per day from this turbine (to the nearest $/day)?

100 * 24 = 2400 kWh * .40= 960 kWh 960 kWh (8 hours a day is a third of kWh) * (1/3)= 320 kWh 320 kWh * 0.08= $25.6 960-320= 640 * 0.04= $24.6 total of $51.2/day

Desired properties of absorber

-Absorptance: fraction of radiation absorbed, or converted to thermal energy (temperature rise), should be high for absorbers -Emittance: fraction of radiation emitted (long-wave), should be low for absorbers -Engineered composite for high performance

Match the appropriate descriptions of solar thermal types for buildings and space-heating applications

-Active: involves a discrete solar collector to gather radiation and requires pump to efficiently move the heat transfer fluid -Passive: solar radiation collection is integrated into the building design to reduce heat loads -Closed loop: a solar heater uses a anti-freeze fluid to heat up the water -solar thermal engines: involved discrete solar collectors with a combination of steam turbines and generators to produce power from higher temperatures achieved

Window options to control Conduction Convection Radiation

-Convection takes place in the air gap, conduction takes place through the glass and across the still air -multiple panes: space between panes filled with heavy gases (i.e. argon, krypton) to reduce convection, or evacuated -low-e coatings: reduce radiative losses in cold climates, radiative gains in hot -low conductance spacers between panes -tightly seal to avoid air leaks -new window technologies: absorbing electrochromic-darkens when sunlight is strong, switchable mirror-can switch between transparent and reflective states

Glass

-Positives: transmittance high for short wavelength solar spectrum, low transmittance for long-wave radiation emitted from absorber, easy to find and inexpensive -Negatives: thermal properties not idea, high conduction losses, breakage in extreme weather events

Hyrdo Power: rate of energy production

-Power=rate of converting potential energy into kinetic energy PE/time= mgh/time mass/time(m/t)= mass flow rate of water (kg/sec) -power=water mass flow rate (kg/sec)*acceleration of gravity (m/s2)* elevation difference(h)= kg m2/s3= joule/sec=watt -How much power is produced when I release 1 kg of water per second from a height of 1 meter? -1 kg/s * 9.8m/s2 * 1 meter= 9.8 watts

Horizonal Wind Turbine Design Solutions

-Relative wind velocity increase with distance from the hub -twisted blades, cord angle changes as you move away from the Hub -Adjustable pitch blades- mechanical adjustment of base angel of angle of attack for different relative wind speed -flexible blades to absorb fluctuating drag -end of blade moving faster

Local Winds

-Sea breezes: result of the seas ability to maintain temperature, day-time land heats, sea is cool. Night-time land cools faster than sea -mountain breezes: wind concentration in mountain passes. One of the first 'wind farm' in the US was in livingston, Montana -Santa Ana Winds (so cal): high pressure inland, low pressure offshore, wind flow down valleys from great basin, valleys act like a nozzle on a hose increasing wind speed

Hydro Energy

-Solar energy 'lifts' water to higher elevations -this energy is stored as potential energy- the ability of this mass of water to fall -how much energy does it take to increase the elevation of 1 kg of water by 1 meter? m*g*h 1m*9.8*1m= 9.8J

Seasonal Changes in Solar Radiation

-Summer: longer 'day' length, better solar angle -Winter: short days, bad solar angle -Higher Latitudes create greater seasonal effect: no geometric effect at the equator -Reduced radiation from cloud cover can also be seasonal

Earth's temperature

-a few feet below the surface, earth temperatures remain relatively constant and moderate -ground temperatures are much milder than average monthly air temperatures -on average around 54F but changes with location

What describes a p-type semiconductor

-absence of an electron from the lattice, giving rise to a hole, implying an overall positive charge

Heat pump applications: shallow low-temp efficiency improvement for heating and cooling

-can save 25-40% on heating and cooling energy -full market penetration: approx. 6% decline in worldwide CO2 -free hot water, less maintenance, quiet, but high first cost

Small/mini hydro applications

-categories not universally defined -micro: <100 kW <1m3/s <0.3m -Mini: 100 to 1,000 kW 1 to 10m3/s 0.3 to 0.8 m -Small: 1 to 50 MW >10m3/s >0.8 m -grid connection: grid-connected, isolated-grid and off-grid -water source: low head, run of river; high head, run of river; dam/reservoir -diversion of waterways and construction of dams increases cost and complexity

Building Insulation and air exchange

-ceiling, wall, foundation, window insulation- reduce conductive heat loss and gain -reduce heat loss/gain from infiltration (or air exchange with outside): double doorways, planned air exchange with heat recovery-control moisture and air quality

Oscillating Water Column

-drives air flow through a turbine to generate electricity -75 kW demonstration unit operated on the scottish island of islay 1989-1999

Heating and cooling (geothermal)

-during the heating season, the earth serves as a heat source (HE- heat of extraction) -during the cooling season, the earth serves as a heat sink (HR- heat of rejection)

Second Law of Thermodynamics

-energy (heat) flows spontaneously from an area of high concentration (hot body) to an area of low concentration (cold body) -always hot to cold, never cold to hot (unless you provide work to drive opposite)

Why do tides happen?

-energy from moon -centrifugal and gravity effects of moon and sun, Rotation of moon around earth and rotation of earth itself -daily and seasonal variation of tides -tides twice daily

Solar Power Tower

-field of heliostats focuses sunlight onto central tower (heliostat: tracking mirror) -concentration ratio 1,500 or more- very high operating temperature -heat absorbed by heat transfer fluid: typically molten salt, heat exchange to drive steam turbine cycle -integrated molten salt thermal storage

wave power compontents

-fixed part or stable reference -moving part that follows wave motion -energy conversion technology

Shading

-full sun in winter-shade in summer -static overhangs -deciduous trees or other plants -on-demand shading devices: solar screens, curtains, shutters

High Head Applications

-high pressure, high velocity, low volume reduces size of storage reservoir -ideal in mountainous areas with favorable sites -high head turbines: high pressure water jet turns impulse turbine blades at .5 water jet speed -pelton 1870s, turgo- 1919 -80-90% mechanical energy conversion efficiency

Low head applications

-high volume, low velocity- minimal storage, run-of-river -barrage also for river level and flood control -fish ladders often needed -Fourneyron's low head turbine developed in 1800s 80% + conversion efficiency -Low head Kaplan Turbine: adjustable pitch propeller blades, adjustable wicket gates, efficient over wide range of flow and head, low head applications 3 to 60 m head

Geothermal heat sources

-hot ground water: temperate suited for space heating, not electricity production -natural steam reservoirs: deep high temperature wells, heat exchange to run a steam turbine -geo-pressured reservoirs: brine saturated with natural gas under pressure, heat exchange to run a steam turbine, may also extract natural gas -hot dry rock: heat exchange to run a steam turbine

Pumped storage system

-hydropower is used for producing electricity from dams on rivers, but it is also useful as an energy storage system- from other renewable or nonrenewable energy sources. If there is excess energy, the excess could be used to pump water into a reservoir at an elevation which can then be released through a turbine when needed ~78% efficiency -most cost effective means for mass storage of electrical energy

Unglazed flat plate (Water)

-inexpensive: no glazing, usually no frame nor insulation on back, usually no selective coating -low temperature rise -most often used for swimming pools

Long term thermal storage: heat collected in summer, used in winter

-long-term thermal storage below ground

Floating devices

-rise and fall according to the motion of the wave and electricity is generated through their motion -the salter duck development was stalled during the 1980s due to a miscalculation in the cost of energy production by a factor of 10

Direct Drive Wind Turbines

-rotor connected to generator -variable speeds- simple turbine, sophisticated electronics -very few moving parts -small diameter (<4ft dia) can be noisy in high winds -typical on turbines <10 kW

Commercial/industrial heating applications

-schools, office buildings, factories- similar technology as for residential applications -some have some needs that residences do not: heating ventilation air, heat for industrial processes -some technologies and more economically viable on large scale

How solar PV is made

-silicon can be 'doped' by replacing a few atoms in lattice -p-type: "positive" doped with 3 valence electron element (usually boron) result: missing electron in lattice -N-type: "negative" doped with 5-valence electron element (usually phosphorus) result: extra electron in lattice -n-type on top of collector, current flows in external circuit

Tidal current prototype

-six 35 kW turbines east river, NY 2007 -verdant energy proposal: mile long series of generators in tidal channel of NY would generate 10 MW -installation costs alone for the pilot project are $2000 per kilowatt and each kWh will cost between 7 and 9 cents to produce

Solar Space Heating and Cooling

-solar availability not coincident with space heating loads- thermal storage required -Solar availability is coincident with space cooling loads- technology to convert solar radiation to cooling energy -Space heating is a major building end use but is not matched with solar availability -most solar radiation available in summer, most space heating needs in winter -solutions: super insulate structure- reduce energy use + efficiency, thermal storage, passive solar heating- building as solar collector to reduce cost

Match the following descriptions to the respective components of solar PV technology

-solar cell: the basic unit of solar photovoltaic technology -solar module: a collection of solar cells -solar array: a collection of modules

What is the best description of how the Trombe Wall passive solar concept works?

-solar radiation during the winter months is captured by the trombe wall and stored as thermal mass and slowly released during the night

Concentrating solar-thermal power (CSP)

-sunlight concentrated using mirrors -only direct/beam radiation can be concentrated -concentration ratio: measured in "suns" if light from 10m2 is concentrated on 1 m2 of absorber surface the concentration ratio is 10 suns -can integrate thermal storage to supply electricity during the evening peak period

Passive/Direct or Indirect domestic hot water: thermosyphon

-tank located above collector: hot fluid rises-no need for a pump -roof must be able to support the weight of tank -freeze resistant collector fluid can be used= indirect

Third concept: the mass flow in to turbine has to be equal to mass flow out

-the mass flow into the turbine has to be same out of the turbine -mass conservation law -also mass flow rate in = mass flow rate out Mass flow in --> turbine --> mass flow out

PV Materials: nanocrystals or quantum dots

-theoretical maximum efficiency much greater than for other technologies -65% thought possible, roughly double today's best cells -research stage

Desired Properties of Glazing

-transmittance: fraction passing through- high for short-wave radiation energy from the sun is short-wave. Low transmittance for long-wave radiation: energy radiated from absorber plate is long wave keep this inside the collector and create the greenhouse effect -reflectance=fraction reflected, glazing should have low reflectance -example of a selective surface: high short wave transmittance, low for long wave transmittance, low reflectance, high insulation, usually an engineered polymer

Effects of concentration of tidal flow

-typical tidal variation in mid-ocean is 0.5 meters -certain land shapes can magnify those effects (such as smaller land openings)

Efficiency of each collector type depends on the temperature rise (above ambient temperature) required for the application

-unglazed are best for 0-10c above ambient -flat-plate are best for 10-50c above ambient -evacuated tubes are best for more than 50c above ambient

Each of these collector type pushes a boundary and is suitable for a particular application

-unglazed flat plate: simplicity and low cost -glazed flat plate: selective glazing and absorbers surfaces to improve heat gain, insulated to reduce heat loss -evacuated tube: minimize heat loss

Concentrating PV

-uses lens or reflector to concentrate light on PV cell, micro concentrator -advantages: manufacturing cost could be much lower than flat-plate, high cost high efficiency photovoltaic cells can be used, high cell efficiencies

Wind power availability at a specific site changes with

-year to year -height above the ground -time of day -month of year

If the overall efficiency of a solar thermal collection system is 25% and the average daily radiation is 0.745 kWh/m2, how many square meters of collector would you need to provide 1500 kWh of heat in one year?

0.745 kWh/m2 * 365= 271.925 1500/271.925= 5.516 5.516/.25= 22 m2

What is the value of the solar constant, or the solar power density (power per surface area, just outside the earth's atmosphere)

1,400 W/m2

Elements of a solar thermal collector

1- glazing or cover- often not glass 2- Absorber- where solar radiation energy is converted into heat energy 3- Insulation- to reduce heat loss to the environment 4&5- flow tubes and header or some way of moving working fluid in and out of collector -not all these are present in all types of collector

Arrange the following components of generating power from a PV system with battery storage based on the order that you would use this system to toast your bagels for breakfast (i.e., flow of energy from one component to another). 1 is first, and 5 is closest to warm breakfast

1- module, 2-array, 3-battery, 4-inverter, 5-toaster

A four-ton water to air heat pump takes 2700 W to operate according to the manual. This heat pump gets its "4 ton" name from the ton referring to a cooling energy rating (refrigerators used to be cooled by ice, with the ton of ice referring to amount that could melt and keep the temperature). If a ton of cooling is equivalent to equal to 12,000 Btu/hr, what is its cooling COP?

12,000 (BTU/hr) * [0.293071 Watts/ 1 (BTU/hr)] = 3516.852 watts/ 2700 watts = 1.30 1.30 * 4 tons= 5.2

Monocrystalline silicon is one of the most common types of Solar PV material used today. The conversion efficiency from solar radiation to electricity for this type of device in field applications is about

15% (chart)

Assume your answer from the previous question is 1800 kWh, the PV system has a battery and inverter for storage and conversion of the generated energy, respectively. The efficiency of the battery is 80%, whereas the efficiency of the inverter is 96%. What are the respective (approximate) DC and AC forms of the energy generated?

1800 x .80= 1440 kWh 1440 x .96= 1382 kWh 1440kWh DC and 1382kWh AC

How many tides (or inflow/outflow cycles) occur per day?

2

For the conditions in the previous question (-20C outside raising to 45C) - If a generic evacuated tube type collector was installed at the residence, what sort of efficiency can be expected from this system (based on the chart provided)?

20-30%

What is the cut-out speed of the Skystream 2.4 turbine?

26 m/s

The receiver tube with the molten salt has 100.0 m2 of surface area that receives the radiation from the parabolic mirrors. How much annual solar energy is collected by the system? Answer in GWh

273 mWh/m2 * 100 m2 = 27265.5 mWh = 27.3 GWh

Consider the ground temperature to be 5 C and the house temperature to be 30 C. What is the theoretical max COP for a cooling heat pump? (Answer with at least 2 sig figs).

273.15+5= 278.15 K 273.15+30= 303.15 K 278.15/(303.15-278.15)= 11.1

What is the cut-in speed of the Skystream 2.4 turbine?

3 m/s

How much energy-per-area is concentrated from the mirrors on to the molten salt in the receiver tube? Answer in MWh/m2 with at least 3 sig figs.

3.03 mWh/m2 * 90 (solar concentration factor) = 273 mWh/m2

Air is moving through a hoop with a cross-sectional area of 100.0 m2 at 8 meters per second.If the density of the air is 1.2 kg/m3, what is the total power in this wind stream (in kW)?

30.72 kW 1/2ρAV= (.5)(1.2)(100)(8)^3

What is the conversion efficiency (power coefficient) from power in the wind to power output from the blades for a modern highly engineered horizontal axis high-tip-speed two blade wind turbine?

35% to 45% (from graph)

The average ambient temperature during the winter months in Madison, WI is 7.0 ∘C. You'd like to have your household provided with hot water at 45.0 ∘C. What is the temperature rise that needs to be attained (in ∘C)?

38 (45-7)

A 13 m2 solar array is installed in area that receives an annual average daily solar resource of 4.32 kWh/m2/day. The project is expected to cost a total of $13,259 over the 16 year lifetime of the project. What is the levelized cost of energy (LCOE) for this solar array project? Answer in $/kWh

4.32 kWh/m2/day * 13m2= 56.16 kWh/day * 365 days* 16years= 327974.4 kWh $13,259/327974.4 kWh= $0.04/kWh

You want to take a hot shower (42°C) with heat provided with domestic solar thermal technology. It is winter in Madison, the ambient temperature is -20°C, and incoming solar radiation is 500 W/m2. Which of the following technologies would be capable of meeting your heating needs? Select all that apply.

42--20= 62/500= .124 --> evacuated tube collector, glazed flat plate collector

Consider a geothermal plant with pipes extracting energy from 50 km2 of area. The plant runs continuously and produces 50 MW of electrical power at a conversion efficiency 15%. What rate of heat transfer (thermal power) is required for the power plant (in MW)?

50 MW electric * (1 MW thermal/ 0.15 MW electric) = 333 MW thermal

What is the Wisconsin requirement on the noise generated by wind turbines?

50 dBA during the day and 45 dBA during the night at a setback distance of 380 m

What is the approximate average power output of a well-designed modern turbine in Columbus, Ohio with a 10 m2 swept area and 50 m hub height? Assume 80% of the Betz limit, 80% conversion efficiency, and air density of 1.0 kg/m3. Use the map to identify Columbus (star) and the maximum range of the wind speed.

500 W (.5)(1)(10)(6.4)^3= 1048.576 *.80* (.593*.80)= 497.44

Desiccant/evaporative chiller

6-7 Desiccant wheel removes moisture from hot humid outside air (reduce humidity) 7-8 Hot dry air is precooled by heat exchange with cool exhaust air (reduce temperature) 8-9 Moisture is added back to air providing evaporative cooling (further reduce temperature) 9 Cool moderate humidity air enters house2-3 Some 'cooling' energy is recovered from exhaust air by heat exchange wheel (increase temperature) 3-4 Solar heat increases exhaust air temperature (further increase temperature)4-5 hot air dry's desiccant wheel (increased humidity)5 Hot humid air exhausted

A site was measured to have an average wind velocity of 5.2 m/s at 13m above ground. If the surface roughness exponent is assumed to be 0.23, what will the predicted wind velocity be at 32m above ground? Answer in the unit of m/s with 2 significant figures.

6.4 V2= V1(H2/H1)alpha= 5.2(32/13)^.23

What would be the wind velocity at 30 m elevations, if the velocity of 5 m/s is measured at 10 m from the ground? The land is level country with foot tall grass with no trees nearby.

6.58 5(30/10)^.25

How much energy is needed to pump back the water to the top of the reservoir (50 m high) during the night at a flow rate of 1000 gpm (in kWh / day with at least 2 sig figs)? Pumping up the mountain is done for a 12-hr period each night during the off-peak energy demand. The pump has a conversion efficiency of 80%

63.167 kg/sec * 9.8 * 50= 30.951 kW * 12 hrs= 371.421 kWh 371.421 kWh / .80 = 465

You have a 30 year wind turbine project that averages 10 kW of power per year (residential) in an area that has an electricity price of $0.12 kWh. If it expected to cost $262,800 to install and maintain the turbine over its lifetime what is the LCOE (in $/kWh).

8760 hours * 30 years = 262800 hours * 10 kW = 2628000 kWh $262800/2628000kWh= .1

In a year, how much electricity is generated by wind at speed of 14 m/s? Answer in kWh

960 400 hours * 2.4 kW

Air is moving at a velocity of 8 m/s through a hoop with cross sectional area of 100.0 m2. If the density of the air is 1.2 kg/m3, what mass flow rate of air is moving through the hoop (in kg/s)?

960 ρAV--> 1.2*100*8=960

Tidal lagoons

A bounded reservoir, no installations yet, requires more structure than barrage

What basic problem has prevented widespread adoption of solar space heating?

A problem of supply and demand: Most solar radiation is available during the summer months, whereas the need is during the winter

How does the power density of wind (W/m2) at 50 meters elevation above the earth's surface compare to the power density at 10 meters above the earths surface?

About double (from wind power classes table)

Pros and Cons

Advantages: there are minimal environmental impacts Disadvantages: complex machines, high variability in power output, protection during storms, obstruction to ship navigation, visual "pollution" of in coastal areas

Solar Chimney

Air heated in 'greenhouse' •Hot air rises up "chimney"spinning turbines •Efficiency improves with chimney height

What is the wind power efficiency limit in theory?

Betz Limit

Negatives to wind power

Bird/bat mortalities, visual impact, noise, flickering of light during sunset/rise, electromagnetic interference

A heat pump operates between temperature -20 oC (253 K) on the cold side and temperature 25 oC (298 K) on the hot side. What is the theoretical COP in cooling? How about maximum COP in heating? If the heat pump delivers 130,000 kJ/h of heating with a total electric input of 9 kW what is the actual COPheating?

COP cooling= 253/298-253= 5.62 COP heating= 298/298-253= 6.62 COP heating: Q/W= 130000kj/h* 1/9kw * 1 kWh/3600 kj= 4.01

Ground source heat pumps (GSHP) are not a "source" of renewable energy because they require electric energy to operate, but rather a way to increase energy efficiency for heating and cooling applications. The efficiency rating of a heat pump that indicates how much heat can be "pumped" with a given amount of work from electrical input is...

COP or Coefficient of performance

Coefficent of performance

COP= Heat transferred/work COP cooling= Tcold/Thot-Tcold COP heating= Thot/Thot-Tcold

Bat Mortality

Cause of Mortality: blunt-force trauma, barotrauma (flying into low pressure vortex from rotating blades) -fatality rates are highly variable among facilities and regionally -highest numbers during fall migration periods -alternatives to reduce mortalities: shutting down nights during bat migration periods, increasing cut-in speeds during bat migration periods (from 4 to 6.5 m/s, 44 to 93% reduction in bat mortalities)

Which location, on average, has the greatest solar power density (power per surface area)? Choose the best answer.

Central Australia

What is an example of a building passive solar element?

Choosing appropriate insulation for different parts of the house

World Solar Annual Radiation

Cloud cover big influence on radiation, highest solar radiation areas north and south of equator -deserts no cloud cover high rainfall and cloud cover on equator so less solar radiation

You have the choice between three potential sites for a wind farm. Each site is located in a different region of Wisconsin. Which site likely has the greatest wind resources? Select the best answer.

Coastal area along Lake Michigan

Tilt of collector

Collector tilt- angle from horizontal -Azimuth: East/West orientation -most radiation per collector area when beam radiation perpendicular to collector surface

Inverter

Converts DC power generated by PV into AC power used in home or on grid -regulates flow of power to/from home and/or grid

Concentrating solar depends on what type of radiation?

Direct or beam radiation -dry desert locations have maximum beam solar availability -in US southwest

Generation of electricity is appropriate for high temperature sources (greater than about >150C)

Early application: dry steam plants using underground steam to directly run turbines ~500C usually, mechanical energy -> electricity

As a general rule of thumb, all solar collectors installed on the earth should be pointed to the south

False

Towers (wind)

Freestanding Lattice: smaller towers easier to construct Monotube: normal larger

Where does the heat of the earth primarily come from?

From the decay of radioactive nuclei with long half-lives that are embedded within the earth

About what fraction of incoming solar radiation is absorbed by the earth's surface?

Half

If we look at the energy efficiency instead of the coefficient of performance for a heating system, we would look at how much useful energy you convert to useful energy, compared to how much energy you put into the system. Therefore a 90% efficient furnace provides 90% of the energy you put into it in the form of heat (thermal energy) for your home (what you want) and the other 10% is "lost". But since no energy is destroyed where does that 10% primarily go?

Heat exhausted outside your house

Market value of solar

High because of coincidence with peak loads

What is an advantage of concentrating solar energy as compared to other solar technologies? Choose the best answer.

It has a smaller land footprint per electricity generated

Solar radiation collection depends on

Latitude, season (earths tilt angle), cloud cover, shading, collector tilt (tracking)

Tidal barrages are examples of which type of hydropower

Low head

PV Materials: Monocrystalline Silicon

Molten high-purity silicon, seed crystal used to grow larger, crystal pure, high-quality crystal, crystals cut into wafers, wasting up to 20% slow and expensive -ribbon growth: thin crystal grown directly, does not need to be cut, edge-defined film-fed growth, thin sheet grows between two seed crystals

Tracking the sun

More solar energy can be collected year-round is the tilt is adjusted a few times a year- can be done manually -some collectors use automatic tracking systems -types of tracking: single axis- follows sun path AM to PM, two axis: track sun path and adjusts tilt keeps collector always parallel to beam radiation east/west horizontal/vertical

Hydrothermal convection systems

More typical new development, heat exchange with geothermal basin -natural steam drives turbines in plants, water removed can be recycles by injection back into reservoir

Autonomous Power Buoy

Navy's near coast anti-terrorism system -ocean power technologies -$4.8M from DOE $2.8M from US Navy

Geopower drawback

Need to have a suitable geothermal resource

The peak rate for the community is 9 cents per kWh, while off-peak purchase rate is 6 cents per kWh. How much daily profit (in $/day with at least 2 sig figs) is created from using the hydro scenario in the previous problem? Assume the pumping occurs for 12 hours during off-peak and the flow release to produce energy is for 12 hours during on-peak.

On peak: 316 * 0.09 = 28.44 off-peak (cost of pumping water): 465 * 0.06 = 27.96 28.44-27.96= $0.48/day

Which of the three main types of wave machines require a two-way Wells Turbine to capture energy from both incoming and outgoing air.

Oscillating water column

Mark true/false of the following items - whether or not they can be employed in building as passive solar elements?

PV modules- false increase insultation and thermal mass- true orientation of the building- true window placement and roof overhang- true

Other devices:

Pelamis: floating offshore, complicated system of pistons and turbines Whale: water runs through turbine as it flows over

how much energy is stored in 1 kg of water that has been lifted 1 meter above its reference point?

Potential Energy = m g h PE = 1 kg x 9.8 m/s2 x 1 meter PE = 9.8 kg m2/s2 PE = 9.8 joules So how much power do I need to lift 1 kg of water 1m once per second? Power = Energy/Time = 9.8 J/s = 9.8 Watts. -If the process is 85% efficient it takes a bit more...9.8 W / 0.85 = 11.5 W

Shading solar collectors

Shading should be minimized, especially when sun high in the sky -seasonal variations must be considered- due to changes in sun's path, due to deciduous trees -impact of shading will very by collector type

Zero Thermal Energy Home: Multiple Approaches To Solar Heating And Cooling

Siting and orientation of building • Room and floor layout • Passive Solar Gain with Shading • Insulation and Thermal mass • Daylighting - Electrical Energy Reduction, Thermal energy gain

Commercial wind turbine foundation

Soil structure affects foundation design

Solar PV capacity U.S

South West highest (arizona and New Mexico area)

Other uses for solar PV

Space- way off the grid, still used: international space station and on to mars Residential, commercial ground mounted utility scale PV system no access to grid (buoy, weather station) transportation vehicles, air transport

Geographic spread of wind projects in the United States is Reasonably Broad

State incentives for renewable energy wind might not be the best in state but incentives need renewable energy -total potential wind generation: 30,949,523 GWh -total potential wind capacity: 10,640,080 MW but probably not practical potential

Geothermal heat pumps use the following for heating and cooling.

Thermal energy difference of the ground versus the air

When looking at a wind turbine power curve, what explains the abrupt drop in power to 0 kW at extremely high wind speeds (select the best answer)?

This happens at the shut-down speed, beyond which it is unsafe to operate the turbine

Match the following wind turbine tower types to their potential applications:

Tilt-down: Small wind turbines Freestanding lattice: Early midsize turbines Monotube: Midsize to large wind turbines

Future Prospects of hydropower

Today: installed capacity 740 GW annual energy production 2,700 TWh/year -Technical potential: annual energy production 15,000 TWh/yr, .5 world total annual electric consumption -Practical potential: large scale development near its limits in developed countries, large scale potential in developing countries, small scale potential all around the world

Limitations of building wind power

Transporting equipment- so large to transport, little easier to transport offshore since can use boat

Locations with high solar resource insolation would also have high PV capacity factors

True

The best tile angle for a solar collector during the winter month in Madison Wisconsin (43 N, 90 W) is somewhere between 45 and near vertical

True

Storage (solar pv)

Typically batteries, charge controller: protects batteries from excessive change and discharge, has additional functions

Absorption vs. re-radiation by latitude

Uneven heating of Earth's surface equalized by wind to move temperature around. Surplus at equator deficit at poles

Absorption chiller

Vapor compression cycle driven by solar thermal energy (and pump and heat sink)

Variable speed turbines with gear boxes

Variable speed- not so simple design, sophisticated electronics -gear boxes mean more moving parts- oil changes -allows for lower RPM rotors -allows for less expensive generators

Water heating applications

Water heating is a considerable building energy end-use and a good match for solar-thermal applications

We want the solar collector glazing materials to have a high transmittance for short-wave radiation, and a low transmittance for long-wave radiation, because

We want to collect the short-wave radiation from the sun, and reflect back the long-wave infrared emitted by the collector

Other opponent arguments (wind)

Wind power costs more- well sited operations are cost competitive with natural gas, excellent sites are cost competitive with coal -reduced land values- two studies found no negative affect in property values -throw accumulated ice-controls will shut down turbine if covered with ice, any ice that falls will be around turbine base

Passive solar design: example high northern latitude

Window placement for winder solar gain, roof angle and overhand for summer shading

History of solar PV

photoelectric effect discovered 1839, wasnt until 1970s increased interest in solar pv, 1990s growth in manufacturing and falling prices

Choose the best definition of solar irradiance

solar power per unit area at a given location

Collector Insulation

-As the collector temperature increases (above the ambient temperature) -more energy is lost to the environment -insulation reduced this loss and allows higher temperature rise- some of the energy loss is also controlled by the glazing

Bird Mortality

-Avian mortality greatly reduced with newer large turbines and control strategies -early california installation, worst case 500+ birds/yr. smaller faster turning turbines, located in area of high concentration of raptors, sited in known flyways with many perching areas nearby. -Judith Gap wind farm-Montana- 4.52 birds per turbine- july 2006-may 2007

Modern large scale applications electrical generation

-Basic characterization of hydro is the elevation difference we are working with low, medium and high head, depends on height difference between reservoir and release -turbine selection depends on: water flow rate, elevation difference (head)

Parts of a solar PV system

-Cell: basic unit, typical voltage produced about 0.5V for silicon, power typically 1-2W -Module: collection of cells connected together, typical voltage 12V or higher, power typically 20-120 W -Array: wire module together with strings

Match the following geothermal energy sources with their corresponding definitions and applications

-Deep well releasing high temperature steam at the surface: natural steam reservoirs -Deep ground water at temperatures that suit space heating (generally not suited for electricity production): hot water reservoirs -Brine saturated with natural gas under pressure, used for both heat and natural gas: geo-pressured reservoirs

Components of solar radiation

-Direct radiation- also called "beam" radiation -diffuse radiation- also called 'sky' radiation -reflected radiation- 'ground' or 'albedo' radiation -flat plate collectors use all three components: concentrating collectors use only direct, or beam radiation

The area of the USA with the best wind resource is,

Central states

Why are turbine on high towers?

Higher wind speeds- higher height above the ground- less friction with ground -less turbulence with height- less blade fatigue -power proportional to cube of wind speed (V^3)

What describes an n-type semiconductor?

Presence of an extra electron inside the lattice, giving rise to an overall negative charge

What happens to the flow of air after passing through a wind turbine?

Pressure drops, cross-sectional area increase, velocity drops

Horizontal axis wind turbine

Rotor consists of blades and what holds them. Yaw drive- steers turbine into correct position

Next using this new case where the system is being designed for the coldest winter temperatures (-20 ∘C), which of the following collector-types would suit the application (select all that apply)?

evacuated tube type

Visual Impacts

-Aesthetics of landscape: individual opinion, water towers, utility towers, communication tower billboard dot landscape with little resistance -often depends on a variety of more complex social and psychological parameters: opposition to change in surroundings, understanding technology, individuals involvement in project -Wisconsin opinion survey found marked preference for onshore over offshore

Conversion Efficiency (wind)

-All of the power in the wind can not be converted to mechanical (then electrical) power -Maximum theoretically power conversion efficiency (wind to mechanical) -betz limit: 0.59, maximum mechanical power extracted from wind blowing through a HOOP at a certain rate (velocity) 0.59x0.5ρAV^3 (power) -Losses caused by: some of the wind goes around (not through) the hoop, wind exiting blade can't be slowed to zero velocity, aerodynamic drag, frictional losses from high velocity wind/turbine

Which of the following are potential downsides (perceived, and some that are true) to implementing wind energy, that need to be accounted for when planning and siting wind farms?

-Concerns of visual impacts, bat and bird mortality, electromagnetic interference, noise considerations, shadow flicker due to rotating turbine blades

Off-shore Wind

-Custom boat for installation-ship has 6 legs that hydraulically lift the boat to create stable crane platform for installing off-shore wind turbines -methods of decreasing capital costs -offshore foundations: type varies with water depth

WECS Power Curve

-Cut-in wind speed: certain wind speed to be efficient enough to run, lower threshold -rated-power: maximum power output, at this windspeed (rated wind speed) machines will start to protect itself and slow down -shut-down wind speed: not safe to operate shuts down -efficiency depends on wind speed and control sophistication--> turbine usually becomes less efficient at higher speeds

WI Wind Potential

-Everyone has some wind -Can be good sites within lower wind areas -Wind is very site specific -ideal commercial site near existing transmission lines -small wind more scattered than wind farms -Southwest and Door Peninsula higher, northwoods pretty low -existing and proposed projects: 14 projects- 650 MW

Energy in Wind

-Kinetic energy in the wind into mechanical power which is converted into electricity by a turbine -Kinetic energy= 0.5mW^2 m=mass(kg) V=velocity(m/s) Energy=(joudes)kgm2/s2 -energy in a finite mass of air moving at a certain velocity -power is the rate of energy removal from the wind-resulting in reduced wind velocity -energy moving through turbine

Airfoil design

-Lift results from pressure differences between the upper and lower surfaces of an airfoil -Bernoulli effect: faster airflow=lower pressure -Maximize life and minimize drag

Example- Wind Shear

-Monitoring tower at 30m in WI -Annual average wind speed of 5.2m/s -rolling farm field with hedge rows and few buildings -wind turbine hub height will be 45m -what is the estimated wind speed at 45m? -what is the surface factor exponent? From WI surface roughness exponent table: alpha-0.35 -V2=V1(H2/H1)^alpha =5.2(45/30)^0.35 =5.2(1.5)^0.35 =5.2(1.15) =5.99m/s

Second Concept: The turbine can not take all of the velocity (KE) from the fluid

-Only some of the initial energy in the fluid is converted -you have a velocity in (and a kinetic energy in), but also a velocity out (and a kinetic energy out) -if there is no velocity out there can be no flow through the turbine High velocity--> turbine-->low velocity

What are the distinctive characteristics of horizontal axis and vertical axis wind turbines? Select whether the statement describes a HAWT or a VAWT.

-Turbine faces the wind: HAWT -Turbine can face any direction: VAWT -Turbine has high efficiency: HAWT -Turbine has low efficiency: VAWT

Vertical Axis Wind Turbines

-Use wind from any direction without need for positioning device, generator on the ground, difficult to manufacture species curved blades, need to be started spinning to develop sustained lift, lower wind speed at ground level limits power generation, limitations to size of swept area, overall efficiency is low -difficult to protect from high winds

Overspeed/high wind protection

-Used to keep turbine from failure in high winds -turn blade axis out of the wind (small turbines) side-facing furling, tilt-up furling -Aerodynamic brakes flaps -feather blades- change angle of attack to kill lift- stall

Total life of project energy produced vs energy inputs to manufacture and operate energy system

-Want high ratio of output to input, wind second best, range depends on availability of resource. Wind can be better than fossil, solar, biomass

Solar Radiation

-Why does the sun emit radiation? The sun: continuous fusion reactor, hydrogen--> helium, other reactions, 6000C surface temp. Emits large amounts of radiation due to high surface temperatures, takes 8 minutes for energy to reach earth -What radiation does the Earth receive? Solar constant = 1367 W/m2 (power) just outside earth's atmosphere, some radiation absorbed by earth's atmosphere -earth receives short wave radiation from sun, earth emits long wave radiation back into space- trapped long wave radiation is the 'greenhouse effect' -about 50% of radiation outside atmosphere makes it to earth, 1/2 reaches surface reflected by atmosphere, clouds, surface

Available power from wind

-Wind energy to mechanical conversion efficiency: coefficient of performance (cP) -Betz Limit=59%-maximum theoretical mechanical conversion efficiency similar to the Carnot for thermal conversion -commercial turbine efficiency= 10%-45% -electric generator efficiency: up to 95% -drivetrain and other losses -available output energy from WECS (wind energy conversion system) summarized by: Kinetic energy (wind)-->mechanical energy (turbine)-->electrical energy (generator)

Off-shore Wind Energy

-Wind speeds are generally higher and less turbulence allowing greater energy production -Denmark experimental off-shore wind farm energy production 20-30% greater than models predicted, wind speeds higher father off-shore, availability about 98% and high capacity~38% -favorable sites: up to 30m to 50m water depth, at least 5km (3.1 mile) from shore -Increase in flora and fauna around foundations: underwater supports offer reef-like structure, higher yields reported from fisherman in the area -Concern: noise echo in water affect Whales and Dolpins -Higher capital costs

Select all of the correct statement(s) regarding windmills and wind turbines

-Windmills are typically drag-based whereas most modern turbines work on the principle of lift -The Dutch four-arm is an example of a drag-type turbine

Calculating Energy from the Wind

-annual total -Energy=Power x Time -power from the wind depends on wind speed WECS conversion efficiency -time is usually estimated assuming an annual average wind speed and a statistical distribution of wind speeds over time -Raleigh or Weibul Distribution with a 'shape factor' to adjust for local conditions (hours per year wind blows at a particular velocity) -wind speeds can change a lot over short periods of time

Wind Machine Design Challenges

-high efficiency at low wind speeds without flying apart at high wind speeds -challenges of capturing more energy- higher towers, long blades, wind shear across the swept diameter- high wind at top reach of blade/lower wind at bottom reach of blade -fatigue failure of "flapping" blades -Ice! -Ultra-high reliability requirements- 8760 hours/year 400,000 miles/year on your car

Windmills vs Turbine? Drag vs lift

-lift device can move faster than wind -Early application of wind was for grinding grain (wind-mill) water-pumping (windmill?) Battery charger--low speed high torque -Wind turbines: wind energy conversion system (WECS), concert wind energy to electricity, -vertical axis turbines: produce electricity or mechanical power

Power in the wind

-often we want to calculate the power available in the wind which is a function of the velocity cubed -to calculate the power available in the wind you have learned -power: KE/time= (1/2mV2)/time= 1/2V2(m/time) -m/time= mass flow rate = cross sectional area x velocity x density = (A V ρ) -Power= 1/2V2 (A V ρ) = 1/2*V^3*A*ρ -Important: it is impossible to get all the power available in the wind converted in a turbine. This is because: a) you will have some losses due to conversion efficiency b) you need some velocity out of the turbine as we have discussed

Higher latitudes receive less radiation per area

-sharper angle of incidence of solar radiation to Earth surface means: more absorbed by atmosphere, radiation less concentrated than near equator (W/m2) -Angle of incidence: angle between incoming radiation and the normal to a surface

Fifth concept: if the velocity is reduced and mass flow rate is the same, then something has to give

-so if the velocity is reduced but the mass flow rate is the same then something has to happen to allow both -depending on system you can have -area increase (in not constrained in pipe) -density decreases (if a gas) -pressure decreases

Betz's Coefficient

-the Betz Coefficient is derived from the principles of conservation of mass and momentum of the air stream flowing through an idealized "actuator disk" that extracts energy from the wind -the factor 16/27 (0.593) is known as Betz's coefficient -if you calculate the power in the wind (or any fluid) by 0.593 you have just calculated the maximum energy that can be extracted -utility scale wind turbines achieve at peak 75% to 80% of the betz limit

Wind Power "classes"

-wind availability in time condensed to "classes" to rate a general geographic location -variations due to local topography may still be substantial -If a high degree of precision is required a wind survey is needed

What is the approximate range of capacity factors for wind power sites?

20% to 40% (wind speed and turbine efficiency chart)

A wind turbine has a 48 m swept diameter, a conversion efficiency of 40%, and can obtain 80% of the Betz coefficient. If the wind velocity is 11 m/s and air density is 1.00 kg/m3, what is the maximum power that the turbine can convert from the wind? Answer in kW with 3 significant figures.

228 (.5)(1.0)(pi*24^2)(11)^3 x(.40)x(.80*.593)= 228520.459 228 kW

At the wind resource depicted by the wind speed distribution chart above, what is the approximate annual frequency (in hr) that the wind can be expected to blow at 14 m/s?

400 hours

If you were standing 150 meters from a modern wind turbine, the noise level from the turbine would be about, 90 dB(A) or comparable to listening to your stereo.

45 dB(a) or comparable to the background noise level inside a house.

You have a 5 MW rated wind turbine installed in a windy area with a 33% capacity factor based on the wind resources. You can sell wind energy generated to the grid at a rate of $0.08/kWh for 12 hours per day during 'on peak' hours and $0.03/kWh for 12 hours during 'off peak' hours. What is the predicted income from the turbine over a year in $? Answer with at least three significant figures.

5 MW x .33= 1.65 MW = 1650 kW 1650 kW x 8760 hr/year= 14454000 kWh 14454000/2= 7227000 7227000 x 0.08= 578160 7227000 x 0.03= 216810 Total= $794,970

The wind velocity distribution in a day is 7 m/s 50% of the time, and 11 m/s the rest of the time. The windmill has a cross-sectional area of 55 square meters. If the density of the air is 1.2 kg per cubic meter, what is the total kinetic energy in this wind stream in kWh in a day. Provide the answer with at least 2 significant figures.

663 power: (.5)PAV^3 (0.5)(1.2)(55)(7)^3= 11319 w x 12 hours= 135.828 kWh (0.5)(1.2)(55)(11)^3= 43923 w x 12 hours= 527 kwh =663 kwh

At what speed is the wind predicted to be blowing most frequently at the above resource site?

7 m/s

Shadow Flicker

At low sun angles in morning or evening Wisconsin rule: must be analyzed in planning process- not cause more than 30 hours per year of shadow flicker at a nonparticipating residence or occupied community building

The following are characteristics of an off-shore wind farm compared to the same wind farm on land (select all that apply).

Average annual wind speeds are higher Capital costs are higher

Where is wind in U.S

Central great plains high, southwest lower

Off-shore Wind Resource/ Potential in U.S

Great Lakes have good potential, both coasts of U.S -Wisconsin Potential Off-Shores: southern Lake Michigan, Green Bay, 9700 MW potential, water depth vs installation, public concern about purity of view-shed, wind speed and water depth

Wind Farm

Group of large high-tech turbines connected to electrical transmission system -scheduled maintenance -heavy, massive equipment

Landuse intensity (wind) for energy production and conservation techniques

Hard for wind because turbines dont take up as much land as entire wind farm land around turbine can usually still be used as agriculture, more land intensive than solar

Efficiency of types of wind turbines

High speed 2/3 blades best can get up to 50% efficiency, vertical ~30% and narrow range of operation, low speed high torque for milling and water pumping ~15%

Surface Roughness Exponent

Off-shore 0.09 short crops / short-grass prairie 0.16 Crops, Tall-grass prairie 0.19 Crop land with hedges 0.21 Scattered trees and hedges 0.24 Trees, hedges, a few buildings 0.29 Suburban 0.31 Woodlands 0.43

Example Calculation (wind) -a wind turbine with a 20m rotor swept area diameter is in a wind with a velocity of 5.0m/s. What is the power output assuming a 90% turbine conversion efficiency and an 80% of Betz's coefficient is obtained? Air density may be assumed to be 1.00 kg/m3

Power (in wind) going into 20m swept area= 1/2*V^2*(A*V*ρ) = 1/2 * V^3 * pi * r2 * ρ (0.5)(5)^3[(3.14)(10)^2](1kg/m3)= 19630 Nm/s = 19.63 kW -Max power from turbine (considering Betz limit and conversion eff)= (19.63 kW) (0.593*0.8)(0.9)= *8.38 kW*

Adjusting for Hub Height

Power law: wind speed increases as you move up V2=V1(H2/H1)^alpha Alpha= wind shear exponent 'typical' = 1/7 (0.14) ranged from 0.1 for very smooth to 0.4 for very rough surfaces -wind speed commonly measure at 10m above a FLAT surface

Electromagnetic Interference

Rotating turbines between transmitter and receiver distort radio/tv signals -depends mainly on: blade material, shape of the tower -tv signals can be distorted: one solution: affected viewers provided with cable service

Increasing the Accuracy of Estimates

Site survey: monitoring towers Anemometers - Wind Speed and direction• At Proposed hub height best• Alternative - measure at 2 to 3 heights to determine wind shear exponent and use Wind Shear Equation• Temperature (for determining air density)• Sample rate 1-3 seconds, 10 minute or hourly recording -compare local wind conditions in time with historical data in the vicinity of your site

WI Surface Roughness Exponent

Smooth hard ground, lake, ocean 0.2 Level country with foot tall grass, tree lines > 1000' away 0.25 Level and uniform open terrain with crops with occasional trees and buildings 500' - 1000' 0.3 Terrain is less open with scattered trees/buildings < 500' 0.35 Terrain is less open, not densely wooded; Tree/buildings < 500' 0.4 Mixed densely wooded areas & open areas; Tree lines >500' away 0.4 Mixed densely wooded areas & farm fields, trees/buildings <500' 0.45 Densely Wooded 0.5 Urban areas with tall buildings 0.6

Where does the wind come from?

Solar heating of the Earth's surface -high pressure vs. low pressure systems -circulation cell patterns: hadley cell (trade winds) ferrel cell, polar cell -natural flow of air created when changes in temperatures cause air to move from high to low pressure areas-> low pressure areas are typically created by warm air -uneven heating of the earth causes uneven air pressure and thus wind, ultimately wind is created by the energy from the sun

Wind energy is ultimately the product of

Solar radiation on the earth's surface

First concept: Energy conversion

Some of the kinetic energy initially the fluid passing through the turbine is converted to rotational energy (work) which is then converted into electrical energy -losses from conversion between energy types

The power curve of a wind turbine gives us the useful power output of the turbine at a specific wind speed. If you have a wind turbine power curve, which of the following additional information will allow you to calculate the useful energy output of the wind turbine over the course of one year?

The annual distribution of wind speed (hours per year that the wind blows at each specific wind speed)

What happens once the wind velocity exceeds the rated wind speed for a wind turbine, but is still below the shut-down wind speed? Pick best answer

The conversion efficiency decreases

What is the major cause of "flapping" blades, which lead to fatigue failure?

The difference between wind velocities at different height.

Tilt-up (guyed) tower

Used on small turbines < ~20 kW can be tilted down to protect from the wind

Annual wind speed frequently distribution

Wind speed is compiled into bins of wind speed to determine total hours per year at a specific wind speed -Energy=power x time when given wind speed- find number of hours per year at that speed and multiple by power from WECS power curve

The power curve of a wind turbine shows the power output of the turbine over its range of operational wind-speed. The power output of a well designed wind turbine increases in which proportion to wind speed up to its maximum rated power output?

Wind velocity cubed

Noise (wind)

Wisconsin rule: 50 dBA during daytime hours and 45 dBA during nighttime hours (about home background noise) -noise greatly reduced in Modern Turbines: design and operation -quieter than many other public sources of noise -Community building/non-participating residence: lessor of 1250 ft (380 m) 3.1xmax blade tip height -participating residence/non participating property line: 1.1xmax blade tip height