Photovoltaics Eenrgy Genertaion Basics

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PhotovoltaicsFrom Wikipedia, the free encyclopedia

Nellis Solar Power Plantat Nellis Air Force Base in the USA. These panels track the sun in one axis.

Photovoltaic SUDI shade is an autonomous and mobile station in France that replenishes energy for electric vehicles using

solar energy.

Solar panels on theInternational Space Station

Photovoltaics (PV) is a method ofgenerating electrical powerby convertingsolar radiationintodirect

currentelectricityusingsemiconductorsthat exhibit thephotovoltaic effect. Photovoltaic power generation

employssolar panelscomposed of a number ofsolar cellscontaining a photovoltaic material. Materials

presently used for photovoltaics includemonocrystalline silicon,polycrystalline silicon,amorphous

silicon,cadmium telluride, andcopper indium gallium selenide/sulfide.[1]Due to the growing demand
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siliconhttp://en.wikipedia.org/wiki/Monocrystalline_siliconhttp://en.wikipedia.org/wiki/Solar_cellhttp://en.wikipedia.org/wiki/Solar_panelhttp://en.wikipedia.org/wiki/Photovoltaic_effecthttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/Solar_radiationhttp://en.wikipedia.org/wiki/Electricity_generationhttp://en.wikipedia.org/wiki/International_Space_Stationhttp://en.wikipedia.org/wiki/Nellis_Solar_Power_Plant


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forrenewable energysources, the manufacturing of solar cells andphotovoltaic arrayshas advanced

considerably in recent years.[2][3][4]

Solar photovoltaics is growing rapidly, albeit from a small base, to a total global capacity of

67,400megawatts(MW) at the end of 2011, representing 0.5% of worldwide electricity demand.[5]The total

power output of the worlds PV capacity run over a calendar year is equal to some 80 billion kWh of electricity.

This is sufficient to cover the annual power supply needs of over 20 million households in the world.[5]More

than 100 countries use solar PV.[6]Installations may be ground-mounted (and sometimes integrated with

farming and grazing)[7]or built into the roof or walls of a building (building-integrated photovoltaics).

Driven by advances in technology and increases in manufacturing scale and sophistication, the cost of

photovoltaics has declined steadily since the first solar cells were manufactured [8]and the levelised cost of

electricity (LCOE) from PV is competitive with conventional electricity sources in an expanding list of

geographic regions.[9]Net meteringand financial incentives, such as preferentialfeed-in tariffsfor solar-

generated electricity, have supported solar PV installations in many countries.[10]With current technology,

photovoltaics recoup the energy needed to manufacture them in 1 to 4 years.[11]

Contents

[hide]

1 Solar cells

2 Current developments

3 Economics

4 Applications

o 4.1 Power stations

o 4.2 In buildings

o 4.3 In transport

o 4.4 Standalone devices

o 4.5 Rural electrification

o 4.6 Solar roadways

o 4.7 Solar Power satellites

5 Advantages

6 Disadvantages

7 See also

8 References

[edit]Solar cells
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Solar cells produce electricity directly from sunlight

Average solar irradiance, watts per square metre. Note that this is for a horizontal surface, whereas solar panels are

normally mounted at an angle and receive more energy per unit area. The small black dots show the area of solar panels

needed to generate all of the world's energy using 8% efficient photovoltaics.

Solar cell productions by region[12]

Main article:Solar cell

Photovoltaics are best known as a method for generating electric power by using solar cells to convert energy

from the sun into a flow of electrons. Thephotovoltaic effectrefers to photons of light exciting electrons into a
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higher state of energy, allowing them to act as charge carriers for an electric current. The photovoltaic effect

was first observed byAlexandre-Edmond Becquerelin 1839.[13][14]The term photovoltaic denotes the unbiased

operating mode of aphotodiodein 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 sun light, which can be used to power equipment or

torecharge a battery. The first practical application of photovoltaics was to power orbiting satellites and

otherspacecraft, but today the majority ofphotovoltaic modulesare used for grid connected power generation.

In this case aninverteris required to convert the DC to AC. There is a smaller market for off-grid power for

remote dwellings,boats,recreational vehicles, electric cars, roadside emergency telephones,remote sensing,

andcathodic protectionofpipelines.

Photovoltaic power generation employssolar panelscomposed of a number ofsolar cellscontaining a

photovoltaic material. Materials presently used for photovoltaics includemonocrystalline silicon,polycrystalline

silicon,amorphous silicon,cadmium telluride, andcopper indium gallium selenide/sulfide.[1]Due to the growing

demand forrenewable energysources, the manufacturing of solar cells andphotovoltaic arrayshas advanced

considerably in recent years.[2][3][4]

Cells require protection from the environment and are usually packaged tightly behind a glass sheet. When

more power is required than a single cell can deliver, cells are electrically connected together to form

photovoltaic modules, or solar panels. A single module is enough to power an emergency telephone, but for a

house or a power plant the modules must be arranged in multiples asarrays.

A significant market has emerged in off-grid locations for solar-power-charged storage-battery based solutions.

These often provide the only electricity available.[15]The first commercial installation of this kind was in 1966 on

Ogami Island in Japan to transitionOgami Lighthousefrom gas torch to fully self-sufficient electrical power.

Due to the growing demand for renewable energy sources, the manufacture of solar cells andphotovoltaic

arrayshas advanced dramatically in recent years.[2][3][4]

Solar photovoltaics is growing rapidly, albeit from a small base, to a total global capacity of

67,400megawatts(MW) at the end of 2011, representing 0.5% of worldwide electricity demand.[5]The total

power output of the worlds PV capacity run over a calendar year is equal to some 80 billion kWh of electricity.

This is sufficient to cover the annual power supply needs of over 20 million households in the world.

[5]

Morethan 100 countries use solar PV.[6]World solar PV capacity (grid-connected) was 7.6 GW in 2007, 16 GW in

2008, 23 GW in 2009, and 40 GW in 2010.[16][17][18]More than 100 countries use solar PV.[6]Installations may be

ground-mounted (and sometimes integrated with farming and grazing)[7]or built into the roof or walls of a

building (building-integrated photovoltaics).
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Photovoltaic power capacity is measured as maximum power output under standardized test conditions (STC)

in "Wp" (Watts peak).[19]The actual power output at a particular point in time may be less than or greater than

this standardized, or "rated," value, depending on geographical location, time of day, weather conditions, and

other factors.[20]Solar photovoltaic arraycapacity factorsare typically under 25%, which is lower than many

other industrial sources of electricity.[21]

The EPIA/GreenpeaceAdvanced Scenario shows that by the year 2030, PV systems could be generating

approximately 1.8 TW of electricity around the world. This means that, assuming a serious commitment is

made toenergy efficiency, enough solar power would be produced globally in twenty-five years time to satisfy

the electricity needs of almost 14% of the worlds population.[22]

[edit]Current developments

Map of solar electricity potential in Europe. Germany is the current leader in the use of photovoltaics, even though it has

lowerinsolationlevels than some other parts of Europe.

Photovoltaic panels based oncrystalline siliconmodules are encountering competition in the market by panels

that employthin-film solar cells(CdTe[23]CIGS,[24]amorphous Si,[25]microcrystalline Si), which had been rapidly

evolving and are expected to account for 31 percent of the global installed power by 2013.[26]However,

precipitous drops in prices for polysilicon and their panels in late 2011 have caused some thin-film makers to

exit the market and others to experience severely squeezed profits.[27]Other developments

includecastingwafers instead of sawing,[28]concentrator modules,'Sliver' cells, andcontinuous

printingprocesses.

TheSan Jose-based company Sunpower produces cells that have an energy conversion ratio of 19.5%, well

above the market average of 1218%.[29]The most efficient solar cell so far is a multi-junction concentrator

solar cell with an efficiency of 43.5%[30]produced by theNational Renewable Energy Laboratoryin April 2011.

The highest efficiencies achieved without concentration includeSharp Corporationat 35.8% using a proprietary

triple-junction manufacturing technology in 2009,[31]and Boeing Spectrolab (40.7% also using a triple-layer

design). A March 2010 experimental demonstration of a design by a Caltech group led byHarry Atwaterwhich

has an absorption efficiency of 85% in sunlight and 95% at certain wavelengths is claimed to have near perfect
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quantum efficiency.[32]However, absorption efficiency should not be confused with the sunlight-to-electricity

conversion efficiency.

For best performance, terrestrial PV systems aim to maximize the time they face the sun.Solar

trackersachieve this by moving PV panels to follow the sun. The increase can be by as much as 20% in winter

and by as much as 50% in summer. Static mounted systems can be optimized by analysis of thesun path.

Panels are often set to latitude tilt, an angle equal to the latitude, but performance can be improved by

adjusting the angle for summer or winter. Generally, as with other semiconductor devices, temperatures above

room temperature reduce the performance of photovoltaics.[33]

A number of solar panels may also be mounted vertically above each other in a tower, if thezenith distanceof

theSunis greater than zero, and the tower can be turned horizontically as a whole and each panels

additionally around a horizontical axis. In such a tower the panels can follow exactly the Sun. Such a device

may be described as aladdermounted on a turnable disk. Each step of that ladder is the middleaxisof a

rectangularsolar panel. In case the zenith distance ofthe Sun gets zero, the ladder may be rotated to the

north or the south to avoid that a solar panel produces a shadow on a lower mounted solar panel. Instead of an

exactly vertical tower one can choose a tower with an axis directed to thepolar star, meaning that it is parallel

to the rotation axis of theEarth. In this case the angle between the axis and the Sun is always larger than 66

degrees. During a day it is only necessary to turn the panels around this axis to follow the Sun.

The 2011 European Photovoltaic Industry Association (EPIA) report predicted that, "The future of the PV

market remains bright in the EU and the rest of the world," the report said. "Uncertain times are causing

governments everywhere to rethink the future of their energy mix, creating new opportunities for a competitive,

safe and reliable electricity source such as PV."[34]2012 could see the installation of 2030 GW of PV about

the same as in 2011. Unfortunately, the industry's capacity continues to expand, to perhaps as much as

38 GW. The resulting glut of supply has crushed prices and profits.[35]By 2015, 131196 GW of photovoltaic

systems could be installed around the globe.[34]

[edit]Economics

Photovoltaic power

worldwideGWp[5]

2005 5.4

2006 7.0
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2007 9.4

2008 15.7

2009 22.9

2010 39.7

2011 67.4

Year end capacities

The output of a photovoltaic array is a product of the area, the efficiency, and the insolation. Thecapacity

factor, or duty cycle, of photovoltaics is relatively low, typically from 0.10 to 0.30, as insolation ranges, by

latitude and prevailing weather, and is location specific from about 2.5 to 7.5 sun hours/day. Panels are rated

under standard conditions by their output power. The DC output is a product of the rated output times the

number of panels times the insolation times the number of days. The sunlight received by the array is affected

by a combination of tilt, tracking and shading. Tracking increases the yield but also the cost, both installation

and maintenance. A dual axis tracker can increase the effective insolation by roughly 35-40%, while

temperature effects can reduce efficiency by 10%. The AC output is roughly 25% lower due to various losses

including the efficiency of the inverter.[36]For example, for a 4 kW array in Paris, where the average insolation is

3 kWh/m/day, the annual (AC) output would be approximately 4kWx3x365x0.75=3285 kWh,[37]and the

monthly output, from the following chart, would range from 67 kWh in December to 498 kWh in July.[38]The

weather strongly affects the output and from year to year monthly and annual outputs can vary substantially.

Published insolation values are normally 10 year averages. There are many live data sites that can

bemonitored, and compared.[39]
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Source: Apricus[40]

Financial incentives for photovoltaics, such asfeed-in tariffs, have often been offered to electricity consumers

to install and operate solar-electric generating systems. Government has sometimes also offered incentives in

order to encourage the PV industry to achieve theeconomies of scaleneeded to compete where the cost of PV-

generated electricity is above the cost from the existing grid. Such policies are implemented to promote

national or territorialenergy independence,high techjob creation and reduction ofcarbon dioxide

emissionswhich cause global warming. Due to economies of scale solar panels get less costly as people use

and buy more as manufacturers increase production to meet demand, the cost and price is expected to drop

in the years to come.

NRELcompilation of best research solar cell efficiencies from 1976 to 2010

According toShi Zhengrong, in 2012 unsubsidized PV systems already produce electricity in some parts of the

world, more cheaply than coal and gas-fired power plants.[41][42]As PV system prices decline it is inevitable that

subsidies will end. "Rapid decline or outright disappearance has already been seen in all the major solar

markets except China and India".[42]

As of 2011, the price of PV modules per MW has fallen by 60 percent since the summer of 2008, according to

Bloomberg New Energy Finance estimates, putting solar power for the first time on a competitive footing with
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the retail price of electricity in a number of sunny countries. There has been fierce competition in the supply

chain, and further improvements in the levelised cost of energy for solar lie ahead, posing a growing threat to

the dominance of fossil fuel generation sources in the next few years.[43]As time progresses, renewable energy

technologies generally get cheaper,[44][45]while fossil fuels generally get more expensive:

The less solar power costs, the more favorably it compares to conventional power, and the more attractive it

becomes to utilities and energy users around the globe. Utility-scale solar power can now be delivered in

California at prices well below $100/MWh ($0.10/kWh) less than most other peak generators, even those

running on low-cost natural gas. Lower solar module costs also stimulate demand from consumer markets

where the cost of solar compares very favorably to retail electric rates.[46]

As of 2011, the cost of PV has fallen well below that of nuclear power and is set to fall further. The average

retail price of solar cells as monitored by the Solarbuzz group fell from $3.50/watt to $2.43/watt over the course

of 2011, and a decline to prices below $2.00/watt seems inevitable:[47]

For large-scale installations, prices below $1.00/watt are common. In some locations, PV has reached grid

parity, the cost at which it is competitive with coal or gas-fired generation. Photovoltaic power is also generated

during a time of day that is close to peak demand (precedes it). More generally, it is now evident that, given a

carbon price of $50/ton, which would raise the price of coal-fired power by 5c/kWh, solar PV will be cost-

competitive in most locations. The declining price of PV has been reflected in rapidly growing installations,

totaling about 23 GW in 2011. Although some consolidation is likely in 2012, as firms try to restore profitability,

strong growth seems likely to continue for the rest of the decade. Already, by one estimate, total investment in

renewables for 2011 exceeded investment in carbon-based electricity generation.[47]

[edit]Applications

80 MWOkhotnykovo Solar Parkin Ukraine.
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PresidentBarack Obamaspeaks at theDeSoto Next Generation Solar Energy Center.

[edit]Power stations

Main articles:Solar parks and solar farmsandList of photovoltaic power stations

Many solarphotovoltaic power stationshave been built, mainly in Europe.[48]As of December 2011, the largest

photovoltaic (PV) power plants in the world are theGolmud Solar Park(China, 200 MW),Sarnia Photovoltaic

Power Plant(Canada, 97 MW),Montalto di Castro Photovoltaic Power Station(Italy, 84.2 MW),FinsterwaldeSolar Park(Germany, 80.7 MW),Okhotnykovo Solar Park(Ukraine, 80 MW),Lieberose Photovoltaic

Park(Germany, 71.8 MW),Rovigo Photovoltaic Power Plant(Italy, 70 MW),Olmedilla Photovoltaic

Park(Spain, 60 MW), and theStrasskirchen Solar Park(Germany, 54 MW).[48]

There are also many large plants under construction. TheDesert Sunlight Solar Farmunder construction

inRiverside County, CaliforniaandTopaz Solar Farmbeing built inSan Luis Obispo County, Californiaare both

550MWsolar parksthat will use thin-film solarphotovoltaicmodules made byFirst Solar.[49]TheBlythe Solar

Power Projectis a 500 MW photovoltaic station under construction inRiverside County, California. TheAgua

Caliente Solar Projectis a 290 megawatt photovoltaic solar generating facility being built inYuma County,

Arizona. TheCalifornia Valley Solar Ranch(CVSR) is a 250megawatt(MW)solar photovoltaicpower plant,

which is being built bySunPowerin theCarrizo Plain, northeast ofCalifornia Valley.[50]The 230 MWAntelope

Valley Solar Ranchis aFirst Solarphotovoltaic project which is under construction in the Antelope Valley area

of the Western Mojave Desert, and due to be completed in 2013.[51]TheMesquite Solar projectis a photovoltaic

solar power plant being built inArlington,Maricopa County,Arizona, owned bySempra Generation.[52]Phase 1

will have anameplate capacityof 150megawatts.[53]

Many of these plants are integrated with agriculture and some use innovative tracking systems that follow the

sun's daily path across the sky to generate more electricity than conventional fixed-mounted systems. There

are no fuel costs or emissions during operation of the power stations.

[edit]In buildings
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kipedia.org/wiki/Agua_Caliente_Solar_Projecthttp://en.wikipedia.org/wiki/Yuma_County,_Arizonahttp://en.wikipedia.org/wiki/Yuma_County,_Arizonahttp://en.wikipedia.org/wiki/Yuma_County,_Arizonahttp://en.wikipedia.org/wiki/Yuma_County,_Arizonahttp://en.wikipedia.org/wiki/California_Valley_Solar_Ranchhttp://en.wikipedia.org/wiki/California_Valley_Solar_Ranchhttp://en.wikipedia.org/wiki/California_Valley_Solar_Ranchhttp://en.wikipedia.org/wiki/Megawatthttp://en.wikipedia.org/wiki/Megawatthttp://en.wikipedia.org/wiki/Megawatthttp://en.wikipedia.org/wiki/Solar_photovoltaichttp://en.wikipedia.org/wiki/Solar_photovoltaichttp://en.wikipedia.org/wiki/Power_planthttp://en.wikipedia.org/wiki/Power_planthttp://en.wikipedia.org/wiki/Power_planthttp://en.wikipedia.org/wiki/SunPowerhttp://en.wikipedia.org/wiki/SunPowerhttp://en.wikipedia.org/wiki/SunPowerhttp://en.wikipedia.org/wiki/Carrizo_Plainhttp://en.wikipedia.org/wiki/Carrizo_Plainhttp://en.wikipedia.org/wiki/Carrizo_Plainhttp://en.wikipedia.org/wiki/California_Valley,_Californiahttp://en.wikipedia.org/wiki/California_Valley,_Californiahttp://en.wikipedia.org/wiki/Photovoltaics#cite_note-49http://en.wikipedia.org/wiki/Photovoltaics#cite_note-49http://en.wikipedia.org/wiki/Photovoltaics#cite_note-49http://en.wikipedia.org/wiki/Solar_power_plants_in_the_Mojave_Desert#Antelope_Valley_Solar_Ranchhttp://en.wikipedia.org/wiki/Solar_power_plants_in_the_Mojave_Desert#Antelope_Valley_Solar_Ranchhttp://en.wikipedia.org/wiki/Solar_power_plants_in_the_Mojave_Desert#Antelope_Valley_Solar_Ranchhttp://en.wikipedia.org/wiki/Solar_power_plants_in_the_Mojave_Desert#Antelope_Valley_Solar_Ranchhttp://en.wikipedia.org/wiki/First_Solarhttp://en.wikipedia.org/wiki/First_Solarhttp://en.wikipedia.org/wiki/First_Solarhttp://en.wikipedia.org/wiki/Photovoltaics#cite_note-50http://en.wikipedia.org/wiki/Photovoltaics#cite_note-50http://en.wikipedia.org/wiki/Mesquite_Solar_projecthttp://en.wikipedia.org/wiki/Mesquite_Solar_projecthttp://en.wikipedia.org/wiki/Mesquite_Solar_projecthttp://en.wikipedia.org/wiki/Arlington,_Arizonahttp://en.wikipedia.org/wiki/Arlington,_Arizonahttp://en.wikipedia.org/wiki/Arlington,_Arizonahttp://en.wikipedia.org/wiki/Maricopa_County,_Arizonahttp://en.wikipedia.org/wiki/Maricopa_County,_Arizonahttp://en.wikipedia.org/wiki/Maricopa_County,_Arizonahttp://en.wikipedia.org/wiki/Arizonahttp://en.wikipedia.org/wiki/Arizonahttp://en.wikipedia.org/wiki/Arizonahttp://en.wikipedia.org/wiki/Sempra_Generationhttp://en.wikipedia.org/wiki/Sempra_Generationhttp://en.wikipedia.org/wiki/Photovoltaics#cite_note-PR-2010-10-51http://en.wikipedia.org/wiki/Photovoltaics#cite_note-PR-2010-10-51http://en.wikipedia.org/wiki/Photovoltaics#cite_note-PR-2010-10-51http://en.wikipedia.org/wiki/Nameplate_capacityhttp://en.wikipedia.org/wiki/Nameplate_capacityhttp://en.wikipedia.org/wiki/Nameplate_capacityhttp://en.wikipedia.org/wiki/Megawatthttp://en.wikipedia.org/wiki/Megawatthttp://en.wikipedia.org/wiki/Photovoltaics#cite_note-sempra-mesquite-52http://en.wikipedia.org/wiki/Photovoltaics#cite_note-sempra-mesquite-52http://en.wikipedia.org/wiki/Photovoltaics#cite_note-sempra-mesquite-52http://en.wikipedia.org/w/index.php?title=Photovoltaics&action=edit&section=6http://en.wikipedia.org/w/index.php?title=Photovoltaics&action=edit&section=6http://en.wikipedia.org/w/index.php?title=Photovoltaics&action=edit&section=6http://en.wikipedia.org/wiki/File:Solar-crop.jpghttp://en.wikipedia.org/wiki/File:Solar-crop.jpghttp://en.wikipedia.org/wiki/File:Solar-crop.jpghttp://en.wikipedia.org/wiki/File:Solar-crop.jpghttp://en.wikipedia.org/w/index.php?title=Photovoltaics&action=edit&section=6http://en.wikipedia.org/wiki/Photovoltaics#cite_note-sempra-mesquite-52http://en.wikipedia.org/wiki/Megawatthttp://en.wikipedia.org/wiki/Nameplate_capacityhttp://en.wikipedia.org/wiki/Photovoltaics#cite_note-PR-2010-10-51http://en.wikipedia.org/wiki/Sempra_Generationhttp://en.wikipedia.org/wiki/Arizonahttp://en.wikipedia.org/wiki/Maricopa_County,_Arizonahttp://en.wikipedia.org/wiki/Arlington,_Arizonahttp://en.wikipedia.org/wiki/Mesquite_Solar_projecthttp://en.wikipedia.org/wiki/Photovoltaics#cite_note-50http://en.wikipedia.org/wiki/First_Solarhttp://en.wikipedia.org/wiki/Solar_power_plants_in_the_Mojave_Desert#Antelope_Valley_Solar_Ranchhttp://en.wikipedia.org/wiki/Solar_power_plants_in_the_Mojave_Desert#Antelope_Valley_Solar_Ranchhttp://en.wikipedia.org/wiki/Photovoltaics#cite_note-49http://en.wikipedia.org/wiki/California_Valley,_Californiahttp://en.wikipedia.org/wiki/Carrizo_Plainhttp://en.wikipedia.org/wiki/SunPowerhttp://en.wikipedia.org/wiki/Power_planthttp://en.wikipedia.org/wiki/Solar_photovoltaichttp://en.wikipedia.org/wiki/Megawatthttp://en.wikipedia.org/wiki/California_Valley_Solar_Ranchhttp://en.wikipedia.org/wiki/Yuma_County,_Arizonahttp://en.wikipedia.org/wiki/Yuma_County,_Arizonahttp://en.wikipedia.org/wiki/Agua_Caliente_Solar_Projecthttp://en.wikipedia.org/wiki/Agua_Caliente_Solar_Projecthttp://en.wikipedia.org/wiki/Riverside_County,_Californiahttp://en.wikipedia.org/wiki/Blythe_Solar_Power_Projecthttp://en.wikipedia.org/wiki/Blythe_Solar_Power_Projecthttp://en.wikipedia.org/wiki/Photovoltaics#cite_note-rew11-48http://en.wikipedia.org/wiki/First_Solarhttp://en.wikipedia.org/wiki/Photovoltaichttp://en.wikipedia.org/wiki/Solar_parkhttp://en.wikipedia.org/wiki/Megawatthttp://en.wikipedia.org/wiki/San_Luis_Obispo_County,_Californiahttp://en.wikipedia.org/wiki/Topaz_Solar_Farmhttp://en.wikipedia.org/wiki/Riverside_County,_Californiahttp://en.wikipedia.org/wiki/Desert_Sunlight_Solar_Farmhttp://en.wikipedia.org/wiki/Photovoltaics#cite_note-PV-47http://en.wikipedia.org/wiki/Strasskirchen_Solar_Parkhttp://en.wikipedia.org/wiki/Olmedilla_Photovoltaic_Parkhttp://en.wikipedia.org/wiki/Olmedilla_Photovoltaic_Parkhttp://en.wikipedia.org/wiki/Rovigo_Photovoltaic_Power_Planthttp://en.wikipedia.org/wiki/Lieberose_Photovoltaic_Parkhttp://en.wikipedia.org/wiki/Lieberose_Photovoltaic_Parkhttp://en.wikipedia.org/wiki/Okhotnykovo_Solar_Parkhttp://en.wikipedia.org/wiki/Finsterwalde_Solar_Parkhttp://en.wikipedia.org/wiki/Finsterwalde_Solar_Parkhttp://en.wikipedia.org/wiki/Montalto_di_Castro_Photovoltaic_Power_Stationhttp://en.wikipedia.org/wiki/Sarnia_Photovoltaic_Power_Planthttp://en.wikipedia.org/wiki/Sarnia_Photovoltaic_Power_Planthttp://en.wikipedia.org/wiki/Golmud_Solar_Parkhttp://en.wikipedia.org/wiki/Photovoltaics#cite_note-PV-47http://en.wikipedia.org/wiki/Photovoltaic_power_stationhttp://en.wikipedia.org/wiki/List_of_photovoltaic_power_stationshttp://en.wikipedia.org/wiki/Solar_parks_and_solar_farmshttp://en.wikipedia.org/w/index.php?title=Photovoltaics&action=edit&section=5http://en.wikipedia.org/wiki/DeSoto_Next_Generation_Solar_Energy_Centerhttp://en.wikipedia.org/wiki/Barack_Obamahttp://en.wikipedia.org/wiki/President_of_the_United_States


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Photovoltaic wall at MNACTEC Terrassa in Spain

Main article:List of rooftop photovoltaic installations

Photovoltaic arrays are often associated with buildings: either integrated into them, mounted on them or

mounted nearby on the ground.

Arrays are most often retrofitted into existing buildings, usually mounted on top of the existing roof structure or

on the existing walls. Alternatively, an array can be located separately from the building but connected by cable

to supply power for the building. In 2010, more than four-fifths of the 9,000 MW of solar PV operating in

Germany were installed on rooftops.[54]Building-integrated photovoltaics (BIPV) are increasingly incorporated

into new domestic and industrial buildings as a principal or ancillary source of electrical power.[55]Typically, an

array is incorporated into the roof or walls of a building. Roof tiles with integrated PV cells are also common. A

2011 study using thermal imaging has shown that solar panels, provided there is an open gap in which air can

circulate between them and the roof, provide a passive cooling effect on buildings during the day and also keep

accumulated heat in at night.[56]

The power output of photovoltaic systems for installation in buildings is usually described inkilowatt-peakunits

(kWp).

[edit]In transport

Main article:Photovoltaics in transport

PV has traditionally been used for electric power in space. PV is rarely used to provide motive power in

transport applications, but is being used increasingly to provide auxiliary power in boats and cars. A self -

containedsolar vehiclewould have limited power and low utility, but asolar-charged vehiclewould allow use of

solar power for transportation. Solar-powered cars have been demonstrated.[57]

[edit]Standalone devices
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Solar parking paystation.

Until a decade or so ago, PV was used frequently to power calculators and novelty devices. Improvements in

integrated circuits and low powerliquid crystal displaysmake it possible to power such devices for several years

between battery changes, making PV use less common. In contrast, solar powered remote fixed devices have

seen increasing use recently in locations where significant connection cost makes grid power prohibitively

expensive. Such applications include water pumps,[58]parking meters,[59][60]emergency telephones,[61]trash

compactors,[62]temporary traffic signs, and remote guard posts and signals.

[edit]Rural electrification

Unlike the past decade, which saw solar solutions purchased mainly by international donors, it is now the locals

who are increasingly opening their wallets to make the switch from their traditional energy means. That is

because solar products prices in recent years have declined to become cheaper than kerosene and batteries.

In Cambodia, for example, villagers can buy a solar lantern at US$25 and use it for years without any extra

costs, where their previous spending on kerosene for lighting was about $2.5 per month, or $30 per year. In

Kenya a solar kit that provides bright light or powers a radio or cell phone costs under $30 at retail stores. By

switching to this kit Kenyans can save $120 per year on kerosene lighting, radio batteries and cell phone

recharging fees.[63]
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Developing countries where many villages are often more than f ive kilometers away from grid power are

increasingly using photovoltaics. In remote locations in India a rural lighting program has been providing solar

powered LED lighting to replace kerosene lamps. The solar powered lamps were sold at about the cost of a

few months' supply of kerosene.[64][65]Cuba is working to provide solar power for areas that are off

grid.[66]These are areas where the social costs and benefits offer an excellent case for going solar though the

lack of profitability could relegate such endeavors to humanitarian goals.

[edit]Solar roadways

The 104kW solar highway along the interchange ofInterstate 5andInterstate 205nearTualatin, Oregonin December 2008.

Main article:Solar roadway

In December 2008, the Oregon Department of Transportation placed in service the nations first solar

photovoltaic system in a U.S. highway right-of-way. The 104-kilowatt (kW) array produces enough electricity to

offset approximately one-third of the electricity needed to light the Interstate highway interchange where it is

located.[67]

A 45 mi (72 km) section of roadway in Idaho is being used to test the possibility of installing solar panels into

the road surface, as roads are generally unobstructed to the sun and represent about the percentage of land

area needed to replace other energy sources with solar power.[68]

[edit]Solar Power satellites

Main article:Solar power satellite

Space-based solar power (SBSP) is the concept of collecting solar power inspacefor use onEarth. It has

been in research since the early 1970s. SBSP would differ from current solar collection methods in that the

means used to collect energy would reside on anorbitingsatelliteinstead of on Earth's surface. Some

projected benefits of such a system are: higher collection rate, longer collection period, and elimination

ofweatherconcerns. SBSP also introduces several new hurdles, primarily the problem of transmitting energy

from orbit to Earth's surface for use.

[edit]Advantages
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The 89PWof sunlight reaching the Earth's surface is plentiful almost 6,000 times more than the 15 TW

equivalent of average power consumed by humans.[69]Additionally, solar electric generation has the highest

power density (global mean of 170 W/m) among renewable energies.[69]

Solar power is pollution-free during use. Production end-wastes and emissions are manageable using existing

pollution controls. End-of-use recycling technologies are under development[70]and policies are being

produced that encourage recycling from producers.[71]

PV installations can operate for many years with little maintenance or intervention after their initial set-up, so

after the initialcapital costof building any solar power plant,operating costsare extremely low compared to

existing power technologies.

Grid-connected solar electricity can be used locally thus reducing transmission/distribution losses (transmission

losses in the US were approximately 7.2% in 1995).[72]

Compared to fossil and nuclear energy sources, very little research money has been invested in the

development of solar cells, so there is considerable room for improvement. Nevertheless, experimentalhigh

efficiency solar cellsalready have efficiencies of over 40% in case of concentrating photovoltaic cells[73]and

efficiencies are rapidly rising while mass-production costs are rapidly falling.[74]

[edit]Disadvantages

In some states of the United States of America, much of the investment in a home-mounted system may be lost

if the home-owner moves and the buyer puts less value on the system than the seller. The city of Berkeley

developed an innovative financing method to remove this limitation, by adding a tax assessment that is

transferred with the home to pay for the solar panels.[75]Now known asPACE, Property Assessed Clean

Energy, 28 U.S. states have duplicated this solution.[76]
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