Photovoltaics (PV) is the field of technology and research related to the application of solar cells for energy by converting sunlight directly into electricity. Due to the growing need for solar energy, the manufacture of solar cells and photovoltaic arrays has expanded dramatically in recent years. [ [ German PV market] ] [ [ BP Solar to Expand Its Solar Cell Plants in Spain and India] ] [ [ Large-Scale, Cheap Solar Electricity] ]

Photovoltaic production has been doubling every two years, increasing by an average of 48 percent each year since 2002, making it the world’s fastest-growing energy technology. At the end of 2007, according to preliminary data, cumulative global production was 12,400 megawatts. [Earth Policy Institute (2007). [ Solar Cell Production Jumps 50 Percent in 2007] ] Roughly 90% of this generating capacity consists of grid-tied electrical systems. Such installations may be ground-mounted (and sometimes integrated with farming and grazing) [ [ GE Invests, Delivers One of World's Largest Solar Power Plants] ] or built into the roof or walls of a building, known as Building Integrated Photovoltaic or BIPV for short. [ [ Building integrated photovoltaics] ]

Financial incentives, such as preferential feed-in tariffs for solar-generated electricity, and net metering, have supported solar PV installations in many countries including Germany, Japan, and the United States. [ [ German PV market] ]


Photovoltaics are best known as a method for generating solar power by using solar cells packaged in photovoltaic modules, often electrically connected in multiples as solar photovoltaic arrays to convert energy from the sun into electricity. To explain the photovoltaic solar panel more simply, photons from sunlight knock electrons into a higher state of energy, creating electricity. The term photovoltaic denotes the unbiased operating mode of a photodiode in which current through the device is entirely due to the transduced light energy. Virtually all photovoltaic devices are some type of photodiode.

Solar cells produce direct current electricity from light, which can be used to power equipment or to recharge a battery. The first practical application of photovoltaics was to power orbiting satellites and other spacecraft, but today the majority of photovoltaic modules are used for grid connected power generation. In this case an inverter is required to convert the DC to AC. There is a smaller market for off grid power for remote dwellings, roadside emergency telephones, remote sensing, and cathodic protection of pipelines.

Cells require protection from the environment and are packaged usually 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 arrays. Although the selling price of modules is still too high to compete with grid electricity in most places, significant financial incentives in Japan and then Germany triggered a huge growth in demand, followed quickly by production.

Perhaps not unexpectedly, a significant market has emerged in urban or grid-proximate locations for solar-power-charged storage-battery based solutions. These are deployed as "stand-by" systems in energy deficient countries like India and as "supplementary" systems in developed markets. In a vast majority of situations such solutions make neither economic nor environmental sense, any green credentials being largely offset by the lead-acid storage systems typically deployed.

The EPIA/Greenpeace Advanced Scenario shows that by the year 2030, PV systems could be generating approximately 2,600 TWh of electricity around the world. This means that, assuming a serious commitment is made to energy efficiency, enough solar power would be produced globally in twenty-five years’ time to satisfy the electricity needs of almost 14% of the world’s population. [ [ Solar Generation V - 2008] ]

Current development

The most important issue with solar panels is capital cost (installation and materials). Newer alternatives to standard crystalline silicon modules including casting wafers instead of sawing, [ [ A Better Way to Make Solar Power] ] thin film (CdTe [ [ Company Information Overview] ] CIGS, [ [ The technology at a glance] ] amorphous Si, [ [ Converting sunlight to electricity] ] microcrystalline Si), concentrator modules, 'Sliver' cells, and continuous printing processes. 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. By early 2006, the average cost per installed watt for a residential sized system was about USD 7.50 to USD 9.50, including panels, inverters, mounts, and electrical items. [ [ Solar Photovoltaic Panels] ] In 2006 investors began offering free solar panel installation in return for a 25 year contract, or Power Purchase Agreement, to purchase electricity at a fixed price, normally set at or below current electric rates. [ [ MMA Renewable Ventures Solar Energy Program] ] [ [ U.S. Retailers Save with Solar PV & Energy Efficiency] ] It is expected that by 2009 over 90% of commercial photovoltaics installed in the United States will be installed using a power purchase agreement. [ [ Solar Power Services: How PPAs are Changing the PV Value Chain] ]

The current market leader in solar panel efficiency (measured by energy conversion ratio) is SunPower, a San Jose based company. Sunpower's cells have a conversion ratio of 23.4%, well above the market average of 12-18%. [ [;jsessionid=97B2227500862822773B5AEB5E5E9DE9?id=40618 SunPower Announces $330 Million Global Solar Supply Agreement With PowerLight] ] However, advances past this efficiency mark are being innovated by engineers at MIT and the California Institute of Technology, and efficiencies of 42% have been achieved at the University of Delaware. [ [ UD-led team sets solar cell record, joins DuPont on $100 million project] retrieved 8 October 2008]

Worldwide installed photovoltaic totals

World solar photovoltaic (PV) market installations reached a record high of 2.8 gigawatts peak (GWp) in 2007. [ MarketBuzz 2008: Annual World Solar Photovoltaic Industry Report] ]

The three leading countries (Germany, Japan and the USA) represent nearly 89% of the total worldwide PV installed capacity. On Wed 1 August 2007, word was published of construction of a production facility in China, which is projected to be one of the largest wafer factories in the world, with a peak capacity of around 1,500MW. [cite journal | author = [ Geoff Nairn] | date = 2007-08-01 Wed 18:14 CEST | title = Shiny prospects for solar equipment makers | journal = [ EngagingChina] | url = | accessdate = 2008-02-14]

Germany was the fastest growing major PV market in the world during 2006 and 2007. In 2007, over 1.3 GWp of PV was installed. The German PV industry generates over 10,000 jobs in production, distribution and installation. By the end of 2006, nearly 88% of all solar PV installations in the EU were in grid-tied applications in Germany. The balance is off-grid (or stand alone) systems. [ [ German PV market] ] Photovoltaic power capacity is measured as maximum power output under standardized test conditions (STC) in "Wp" (Watts peak). [cite book | title = Handbook of Photovoltaic Science and Engineering | author = Antonio Luque and Steven Hegedus | url = | publisher = John Wiley and Sons | year = 2003 | isbn = 0471491969] 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. [ [ The PVWatts Solar Calculator] ] Solar photovoltaic array capacity factors are typically under 25%, which is lower than many other industrial sources of electricity. [ [ UtiliPoint International, Inc. 'Issue alert - What is a megawatt?] ] Therefore the 2006 installed base peak output would have provided an average output of 1.2 GW (assuming 20% × 5,862 MWp). This represented 0.06 percent of global demand at the time. [ [ Total electric power consumption] ]

Grid parity

Grid parity, the point at which photovoltaic electricity is equal to or cheaper than grid power, is achieved first in areas with abundant sun and high costs for electricity such as in California and Japan. [ [ Going for grid parity] 2005 article]

Grid parity has been reached in Hawaii and other islands that otherwise use diesel fuel to produce electricity.

George W. Bush has set 2015 as the date for grid parity in the USA. [ [ Gaining on the grid] ] [ [,%20when%20the%20cost%20of%20solar%20energy%20equals%20that%20of%20grid%20electricity The Path to Grid Parity] (Graphic)] . Abengoa Solar has announced the award of two R&D projects in the field of Concentrating Solar Power (CSP) by the US Department of Energy that total over $14 million. The goal of the DOE R&D program, working in collaboration with partners such as Abengoa Solar, is to develop C.S.P. technologies that are competitive with conventional energy sources (grid parity) by 2015 [] .

General Electric's Chief Engineer predicts grid parity without subsidies in sunny parts of the United States by around 2015. Other companies predict an earlier date [ [] ] : the cost of solar power will be below grid parity for more than half of residential customers and 10% of commercial customers in the OECD, as long as grid electricity prices do not decrease through 2010 [ ] .

The fully-loaded cost (cost not price) of solar electricity is $0.25/kWh or less in most of the OECD countries. Within three years, the fully-loaded cost is likely to fall below $0.15/kWh for most of the OECD and reach $0.10/kWh in sunnier regions. These cost levels are driving three emerging trends [] :
# vertical integration of the supply chain;
# origination of power purchase agreements (PPAs) by solar power companies;
# unexpected risk for traditional Gencos, grid operators and turbine manufacturers.

Financial incentives

The political purpose of incentive policies for PV is to grow the industry even where the cost of PV is significantly above grid parity, to allow it to achieve the economies of scale necessary to reach grid parity. The policies are implemented to promote national energy independence, high tech job creation and reduction of CO2 emissions.

Three incentive mechanisms are used (often in combination):
* investment subsidies: the authorities refund part of the cost of installation of the system,
* Feed-in Tariffs (FIT)/Net metering: the electricity utility buys PV electricity from the producer under a multiyear contract at a guaranteed rate.
* Renewable Energy Certificates ("RECs")

With investment subsidies, the financial burden falls upon the taxpayer, while with feed-in tariffs the extra cost is distributed across the utilities' customer bases. While the investment subsidy may be simpler to administer, the main argument in favour of feed-in tariffs is the encouragement of quality. Investment subsidies are paid out as a function of the nameplate capacity of the installed system and are independent of its actual power yield over time, thus rewarding the overstatement of power and tolerating poor durability and maintenance. Some electric companies offer rebates to their customers, such as Austin Energy in Texas, which offers $4.50/watt installed up to $13,500. [ [ Solar Rebate Program] ]

With feed-in tariffs, the financial burden falls upon the consumer. They reward the number of kilowatt-hours produced over a long period of time, but because the rate is set by the authorities, it may result in perceived overpayment. The price paid per kilowatt-hour under a feed-in tariff exceeds the price of grid electricity. Net metering refers to the case where the price paid by the utility is the same as the price charged. Net metering is particularly important because it can be done with no changes to standard electricity meters, which accurately measure power in both directions and automatically report the difference, and because it allows homeowners and businesses to generate electricity at a different time from consumption, effectively using the grid as a giant storage battery. As more photovoltaics are used ultimately storage will need to be provided, normally in the form of pumped hydro-storage. Normally with net metering deficits are billed each month, while surpluses are rolled over to the following month and paid annually.

Where price setting by supply and demand is preferred, RECs can be used. In this mechanism, a renewable energy production or consumption target is set, and the consumer or producer is obliged to purchase renewable energy from whoever provides it the most competitively. The producer is paid via an REC. In principle this system delivers the cheapest renewable energy, since the lowest bidder will win. However, uncertainties about the future value of energy produced are a brake on investment in capacity, and the higher risk increases the cost of capital borrowed.

The Japanese government through its Ministry of International Trade and Industry ran a successful programme of subsidies from 1994 to 2003. By the end of 2004, Japan led the world in installed PV capacity with over 1.1 GW. [ [] ]

In 2004, the German government introduced the first large-scale feed-in tariff system, under a law known as the 'EEG' (Erneuerbare Energien Gesetz) which resulted in explosive growth of PV installations in Germany. At the outset the FIT was over 3x the retail price or 8x the industrial price. The principle behind the German system is a 20 year flat rate contract. The value of new contracts is programmed to decrease each year, in order to encourage the industry to pass on lower costs to the end users. The programme has been more successful than expected with over 1GW installed in 2006, and political pressure is mounting to decrease the tariff to lessen the future burden on consumers.

Subsequently Spain, Italy, Greece and France introduced feed-in tariffs. None have replicated the programmed decrease of FIT in new contracts though, making the German incentive relatively less and less attractive compared to other countries. The French FIT offers a uniquely high premium (EUR 0.55/kWh) for building integrated systems. California, Greece, France and Italy have 30-50% more insolation than Germany making them financially more attractive.

In 2006 California approved the 'California Solar Initiative', offering a choice of investment subsidies or FIT for small and medium systems and a FIT for large systems. The small-system FIT of $0.39 per kWh (far less than EU countries) expires in just 5 years, and the alternate "EPBB" residential investment incentive is modest, averaging perhaps 20% of cost. All California incentives are scheduled to decrease in the future depending as a function of the amount of PV capacity installed.

At the end of 2006, the Ontario Power Authority (Canada) began its [ Standard Offer Program] , the first in North America for small renewable projects (10MW or less). This guarantees a fixed price of $0.42 CDN per kWh over a period of twenty years. Unlike net metering, all the electricity produced is sold to the OPA at the SOP rate. The generator then purchases any needed electricity at the current prevailing rate (e.g., $0.055 per kWh). The difference should cover all the costs of installation and operation over the life of the contract.

The price per kilowatt hour or per peak kilowatt of the FIT or investment subsidies is only one of three factors that stimulate the installation of PV. The other two factors are insolation (the more sunshine, the less capital is needed for a given power output) and administrative ease of obtaining permits and contracts.

Unfortunately the complexity of approvals in California, Spain and Italy has prevented comparable growth to Germany even though the return on investment is better.

In some countries, additional incentives are offered for BIPV compared to stand alone PV.
* France + EUR 0.25/kWh (EUR 0.30 + 0.25 = 0.55/kWh total)
* Italy + EUR 0.04-0.09 kWh
* Germany + EUR 0.05/kWh (facades only)

Environmental impacts

Unlike fossil fuel based technologies, solar power does not lead to any harmful emissions during operation, but the production of the panels leads to some amount of pollution. This is often referred to as the energy input to output ratio. In some analysis, if the energy input to produce it is higher than the output it produces it can be considered environmentally more harmful than beneficial. Also, placement of photovoltaics affects the environment. If they are located where photosynthesizing plants would normally grow, they simply substitute one potentially renewable resource (biomass) for another. It should be noted, however, that the biomass cycle converts solar radiation energy to electrical energy with significantly less efficiency than photovoltaic cells alone. And if they are placed on the sides of buildings (such as in Manchester) or fences, or rooftops (as long as plants would not normally be placed there), or in the desert they are purely additive to the renewable power base.

Greenhouse gases

Life cycle greenhouse gas emissions are now in the range of 25-32 g/kWh and this could decrease to 15 g/kWh in the future. Alsema, E.A.; Wild - Scholten, M.J. de; Fthenakis, V.M." [ Environmental impacts of PV electricity generation - a critical comparison of energy supply options] " ECN, September 2006; 7p.Presented at the 21st European Photovoltaic Solar Energy Conference and Exhibition, Dresden, Germany, 4-8 September 2006.] For comparison, a combined cycle gas-fired power plant emits some 400 g/kWh and a coal-fired power plant 915 g/kWh and with carbon capture and storage some 200 g/kWh. Only nuclear power and wind are better, emitting 6-25 g/kWh and 11 g/kWh on average. Using renewable energy sources in manufacturing and transportation would further drop photovoltaic emissions.


One issue that has often raised concerns is the use of cadmium in cadmium telluride solar cells (CdTe is only used in a few types of PV panels). Cadmium in its metallic form is a toxic substance that has the tendency to accumulate in ecological food chains. The amount of cadmium used in thin-film PV modules is relatively small (5-10 g/m²) and with proper emission control techniques in place the cadmium emissions from module production can be almost zero. Current PV technologies lead to cadmium emissions of 0.3-0.9 microgram/kWh over the whole life-cycle. Most of these emissions actually arise through the use of coal power for the manufacturing of the modules, and coal and lignite combustion leads to much higher emissions of cadmium. Life-cycle cadmium emissions from coal is 3.1 microgram/kWh, lignite 6.2, and natural gas 0.2 microgram/kWh.

Note that if electricity produced by photovoltaic panels were used to manufacture the modules instead of electricity from burning coal, cadmium emissions from coal power usage in the manufacturing process could be entirely eliminated.

Energy Payback Time and Energy Returned on Energy Invested

The energy payback time is the time required to produce an amount of energy as great as what was consumed during production. The energy payback time is determined from a life cycle analysis of energy.

Another key indicator of environmental performance, tightly related to the energy payback time, is the ratio of electricity generated divided by the energy required to build "and maintain" the equipment. This ratio is called the energy returned on energy invested (EROEI). Of course, little is gained if it takes as much energy to produce the modules as they produce in their lifetimes. This should not be confused with the economic return on investment, which varies according to local energy prices, subsidies available and metering techniques.

Life-cycle analyses show that the energy intensity of typical solar photovoltaic technologies is rapidly evolving. In 2000 the energy payback time was estimated as 8 to 11 years [ Andrew Blakers and Klaus Weber, [ “The Energy Intensity of Photovoltaic Systems”] , Centre for Sustainable Energy Systems, Australian National University, 2000. ] , but more recent studies suggest that technological progress has reduced this to 1.5 to 3.5 years for crystalline silicon PV systems.

Thin film technologies now have energy pay-back times in the range of 1-1.5 years (S.Europe). With lifetimes of such systems of at least 30 years, the EROEI is in the range of 10 to 30.They thus generate enough energy over their lifetimes to reproduce themselves many times (6-31 reproductions, the EROEI is a bit lower) depending on what type of material, balance of system (or BOS), and the geographic location of the system. [ Joshua Pearce and Andrew Lau, [ “Net Energy Analysis For Sustainable Energy Production From Silicon Based Solar Cells”] , Proceedings of American Society of Mechanical Engineers Solar 2002: Sunrise on the Reliable Energy Economy, editor R. Campbell-Howe, 2002. ]


*Cost may not cover lifespan savings unless a preferencial feed-in tarif is offered by the grid network. But this depends on location and energy prices.
*Solar electricity is often more expensive than electricity generated by other sources.
*Solar electricity is not available at night and is less available in cloudy weather conditions. Therefore, a storage or complementary power system is required.
*Limited power density: Average daily insolation in the contiguous U.S. is 3-7 kW·h/m² [ [ NREL Map of Flat Plate Collector at Latitude Tilt Yearly Average Solar Radiation] ] [ [ Solar Energy Technologies Program: Solar FAQs] US Department of Energy. Retrieved on 24 August 2007,] [ [ Solar panel achieves high efficiency] ] and on average lower in Europe.
*Solar cells produce DC which must be converted to AC (using a grid tie inverter) when used in currently existing distribution grids. This incurs an energy loss of 4-12%. [ [ Renewable Resource Data Center - PV Correction Factors] ]


*The 89 petawatts of sunlight reaching the earth's surface is plentiful - almost 6,000 times more than the 15 terawatts of average power consumed by humans. [ Vaclav Smil - Energy at the Crossroads] ] Additionally, solar electric generation has the highest power density (global mean of 170 W/m²) among renewable energies.
*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. [ [ Environmental Aspects of PV Power Systems] ]
*Facilities can operate with little maintenance or intervention after initial setup.
*Solar electric generation is economically superior where grid connection or fuel transport is difficult, costly or impossible. Examples include satellites, island communities, remote locations and ocean vessels.
*When grid-connected, solar electric generation can displace the highest cost electricity during times of peak demand (in most climatic regions), can reduce grid loading, and can eliminate the need for local battery power for use in times of darkness and high local demand; such application is encouraged by net metering. Time-of-use net metering can be highly favorable to small photovoltaic systems.
*Grid-connected solar electricity can be used locally thus reducing transmission/distribution losses (transmission losses were approximately 7.2% in 1995). [ [ U.S. Climate Change Technology Program - Transmission and Distribution Technologies] ]
*Once the initial capital cost of building a solar power plant has been spent, operating costs are extremely low compared to existing power technologies.
*Compared to fossil and nuclear energy sources, very little research-money has been invested in the development of solar cells, so there is much room for improvement. Nevertheless, experimental high efficiency solar cells already have efficiencies of over 40% and efficiencies are rapidly rising while mass production costs are rapidly falling. [ [] ]

Photovoltaics companies

Photovoltaic industry associations

* [ ASIF: Spanish PV Industry Association] "in Spanish only"
* [ SER: french renewable energy Industry organization] "in French only"
* [ BSW: German Solar Industry Association] "in German, with English summary"
* [ Canadian Solar industry Association]
* [ EPIA: European Photovoltaic Industry association]
* [ IPVEA: International Photovoltaic Equipment Association]
* [ JPEA: Japanese Photovoltaic Energy Association] "in Japanese only"
* [ SEIA: Solar Energy Industries Association] US trade association
* [ SEMI: Semiconductor Equipment and Materials International] Global industry association

Photovoltaics research institutes

There are many research institutions and departments at universities around the world who are active in photovoltaics research. [ [ School of Photovoltaic and Renewable Energy Engineering] ] [ [ Arizona State University Photovoltaic Testing Laboratory] ] Countries which are particularly active include Germany, Spain, Japan, Australia, China, and the USA.

Some universities and institutes which have a photovoltaics research department.
* [ Solar Energy Materials Research Group] at Lawrence Berkeley National Laboratory
* [ EuPD Research, Worldwide PV Market Research]
* [ The Center for Functional Nanomaterials] at Brookhaven National Laboratory
* [ Solar Energy Laboratory] at University of Southampton
* [ National Renewable Energy Laboratory NREL]
* [ Energy & Environmental Technology Application Center] at the College of Nanoscale Science and Engineering SUNY at Albany
* [ Institut für Solare Energiesysteme ISE] at the Fraunhofer Institute
* [ Energy research Centre of the Netherlands (ECN)]
* [ Imperial College London: Experimental Solid State Physics]
* [ Instituto de Energía Solar] , at [ Universidad Politécnica de Madrid]
* [ Centre for Renewable Energy Systems Technology] , at [ Loughborough University]
* School of Photovoltaic and Renewable Energy Engineering at The University of New South Wales
* [ Centre for Sustainable Energy Systems] at the Australian National University
* [ Ecole Polytechnique Fédérale de Lausanne] Prof. Graetzel invented dye sensitized cells here
* [ Advanced Energy Systems] at Helsinki University of Technology
* [ Institute of Materials Research, Salford University]
* [ The Centre for Electronic Devices and Materials] at Sheffield Hallam University
* [ The Centre for Advanced Investigations on Electric Engineering] at The National Polytechnic Institute of Mexico
* [ The Solar Caliometry Lab] at Queen's University
* [ Institute of microtechnology] at [ University of Neuchatel Switzerland]
* [ University of Konstanz]
* [ Arizona State University Photovoltaic Testing Laboratory]
* [ Institute of Energy Conversion] at [ University of Delaware]
* [ World Alliance for Decentralized Energy]
* Florida Solar Energy Center at [ University of Central Florida]
* [ Linz Institute for Organic Solar Cells (LIOS)]

ee also

* Active solar
* Carbon nanotubes in photovoltaics
* Concentrator photovoltaics
* Deployment of solar power to energy grids
* Distributed Energy Resources
* Electranet
* Fluorescent solar collector
* Green technology
* Grid-tied electrical system
* High efficiency solar cells
* Infrared
* Islanding
* Low cost solar cell
* Maximum power point tracker
* Microgeneration
* Microgeneration Certification Scheme
* Photoelectrochemical cell
* Photovoltaic and renewable energy engineering in Australia
* Photovoltaics in transport
* Renewable Energy Focus magazine
* Renewable energy
* Renewable energy in the European Union
* Solar vehicle
* Solar thermal energy
* Solar energy
* Solar cell
* Solar panel
* Solar air conditioning
* World Council for Renewable Energy


External links

;Publicly funded free data sources
* [ EU PV Technology Platform - forum for stakeholders to influence EU policy,]
* [ Trends in photovoltaic applications in selected IEA countries between 1992 and 2004]
* [ IEA PVPS annual report 2006]
* [ Photovoltaic Geographical Information System (PVGIS)]
* [ US Department of Energy - Energy Efficiency and Renewable Energy]
* [ DSIRE] Listing of US state, local, utility, and federal incentives for renewable energy and energy efficiency.
* [ Find Solar] US solar estimator and solar pro locator (joint partnership with DOE).
* [ PV Estimation Utility for Europe and Africa] European Commission Joint Research Centre

;Trade Press and commercial databases
* [ Photovoltaics International Journal] Online news and in print technical articles from around the world
* [ Solarbuzz] Online news
* [ SolarPlaza] Trade and information
* [ Photon International] International PV magazine, also has local editions for Germany and Spain
* [ ENF Ltd] PV Market Research and Industry Directory
* [ Renewable Energy Focus magazines] The International Renewable Energy Magazine

;Trade shows
* [ European Photovoltaic Solar Energy Conference] 1st to 5 September 2008
* [ Solar Power 2008 San Diego] October 13-16, 2008

* [ The Thin-film Future] Munich, 26th May 2009
* [ Global demand Conference] , 2nd September 2008, Valencia

;Live data
* [ Europe]
* [ Germany]
* [ United States]
* [ New Zealand schools]

* [ World's largest photovoltaic power plants]
* [ Real-Time Performance Diagnostics]

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