The Info List - Solar Energy

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Solar energy
Solar energy
is radiant light and heat from the Sun
that is harnessed using a range of ever-evolving technologies such as solar heating, photovoltaics, solar thermal energy, solar architecture, molten salt power plants and artificial photosynthesis.[1][2] It is an important source of renewable energy and its technologies are broadly characterized as either passive solar or active solar depending on how they capture and distribute solar energy or convert it into solar power. Active solar
Active solar
techniques include the use of photovoltaic systems, concentrated solar power and solar water heating to harness the energy. Passive solar
Passive solar
techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light-dispersing properties, and designing spaces that naturally circulate air. The large magnitude of solar energy available makes it a highly appealing source of electricity. The United Nations Development Programme in its 2000 World Energy
Assessment found that the annual potential of solar energy was 1,575–49,837 exajoules (EJ). This is several times larger than the total world energy consumption, which was 559.8 EJ in 2012.[3][4] In 2011, the International Energy Agency
International Energy Agency
said that "the development of affordable, inexhaustible and clean solar energy technologies will have huge longer-term benefits. It will increase countries’ energy security through reliance on an indigenous, inexhaustible and mostly import-independent resource, enhance sustainability, reduce pollution, lower the costs of mitigating global warming, and keep fossil fuel prices lower than otherwise. These advantages are global. Hence the additional costs of the incentives for early deployment should be considered learning investments; they must be wisely spent and need to be widely shared".[1]


1 Potential 2 Thermal energy

2.1 Early commercial adaptation 2.2 Water
heating 2.3 Heating, cooling and ventilation 2.4 Cooking 2.5 Process heat 2.6 Water
treatment 2.7 Molten salt
Molten salt

3 Electricity

3.1 Photovoltaics 3.2 Concentrated solar power

4 Architecture and urban planning 5 Agriculture
and horticulture 6 Transport 7 Fuel production 8 Energy storage
Energy storage
methods 9 Development, deployment and economics 10 ISO standards 11 See also 12 Notes 13 References 14 External links

Potential Further information: Solar radiation

About half the incoming solar energy reaches the Earth's surface.

Average insolation. The theoretical area of the small black dots is sufficient to supply the world's total energy needs of 18 TW with solar power.

The Earth receives 174 petawatts (PW) of incoming solar radiation (insolation) at the upper atmosphere.[5] Approximately 30% is reflected back to space while the rest is absorbed by clouds, oceans and land masses. The spectrum of solar light at the Earth's surface is mostly spread across the visible and near-infrared ranges with a small part in the near-ultraviolet.[6] Most of the world's population live in areas with insolation levels of 150–300 watts/m², or 3.5–7.0 kWh/m² per day.[citation needed] Solar radiation
Solar radiation
is absorbed by the Earth's land surface, oceans – which cover about 71% of the globe – and atmosphere. Warm air containing evaporated water from the oceans rises, causing atmospheric circulation or convection. When the air reaches a high altitude, where the temperature is low, water vapor condenses into clouds, which rain onto the Earth's surface, completing the water cycle. The latent heat of water condensation amplifies convection, producing atmospheric phenomena such as wind, cyclones and anti-cyclones.[7] Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14 °C.[8] By photosynthesis, green plants convert solar energy into chemically stored energy, which produces food, wood and the biomass from which fossil fuels are derived.[9] The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year.[10] In 2002, this was more energy in one hour than the world used in one year.[11][12] Photosynthesis
captures approximately 3,000 EJ per year in biomass.[13] The amount of solar energy reaching the surface of the planet is so vast that in one year it is about twice as much as will ever be obtained from all of the Earth's non-renewable resources of coal, oil, natural gas, and mined uranium combined,[14]

Yearly solar fluxes & human consumption1

Solar 3,850,000 [10]

Wind 2,250 [15]

potential ~200 [16]

Primary energy use2 539 [17]

Electricity2 ~67 [18]

1 Energy
given in Exajoule (EJ) = 1018 J = 278 TWh  2 Consumption as of year 2010

The potential solar energy that could be used by humans differs from the amount of solar energy present near the surface of the planet because factors such as geography, time variation, cloud cover, and the land available to humans limit the amount of solar energy that we can acquire. Geography affects solar energy potential because areas that are closer to the equator have a greater amount of solar radiation. However, the use of photovoltaics that can follow the position of the sun can significantly increase the solar energy potential in areas that are farther from the equator.[4] Time variation effects the potential of solar energy because during the nighttime there is little solar radiation on the surface of the Earth for solar panels to absorb. This limits the amount of energy that solar panels can absorb in one day. Cloud cover
Cloud cover
can affect the potential of solar panels because clouds block incoming light from the sun and reduce the light available for solar cells. In addition, land availability has a large effect on the available solar energy because solar panels can only be set up on land that is otherwise unused and suitable for solar panels. Roofs have been found to be a suitable place for solar cells, as many people have discovered that they can collect energy directly from their homes this way. Other areas that are suitable for solar cells are lands that are not being used for businesses where solar plants can be established.[4] Solar technologies are characterized as either passive or active depending on the way they capture, convert and distribute sunlight and enable solar energy to be harnessed at different levels around the world, mostly depending on distance from the equator. Although solar energy refers primarily to the use of solar radiation for practical ends, all renewable energies, other than Geothermal power
Geothermal power
and Tidal power, derive their energy either directly or indirectly from the Sun. Active solar
Active solar
techniques use photovoltaics, concentrated solar power, solar thermal collectors, pumps, and fans to convert sunlight into useful outputs. Passive solar
Passive solar
techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air, and referencing the position of a building to the Sun. Active solar
Active solar
technologies increase the supply of energy and are considered supply side technologies, while passive solar technologies reduce the need for alternate resources and are generally considered demand side technologies.[19] In 2000, the United Nations Development Programme, UN Department of Economic and Social Affairs, and World Energy Council
World Energy Council
published an estimate of the potential solar energy that could be used by humans each year that took into account factors such as insolation, cloud cover, and the land that is usable by humans. The estimate found that solar energy has a global potential of 1,575–49,837 EJ per year (see table below).[4]

Annual solar energy potential by region (Exajoules) [4]

Region North America Latin America and Caribbean Western Europe Central and Eastern Europe Former Soviet Union Middle East and North Africa Sub-Saharan Africa Pacific Asia South Asia Centrally planned Asia Pacific OECD

Minimum 181.1 112.6 25.1 4.5 199.3 412.4 371.9 41.0 38.8 115.5 72.6

Maximum 7,410 3,385 914 154 8,655 11,060 9,528 994 1,339 4,135 2,263


Total global annual solar energy potential amounts to 1,575 EJ (minimum) to 49,837 EJ (maximum) Data reflects assumptions of annual clear sky irradiance, annual average sky clearance, and available land area. All figures given in Exajoules.

Quantitative relation of global solar potential vs. the world's primary energy consumption:

Ratio of potential vs. current consumption (402 EJ) as of year: 3.9 (minimum) to 124 (maximum) Ratio of potential vs. projected consumption by 2050 (590–1,050 EJ): 1.5–2.7 (minimum) to 47–84 (maximum) Ratio of potential vs. projected consumption by 2100 (880–1,900 EJ): 0.8–1.8 (minimum) to 26–57 (maximum)

Source: United Nations Development Programme
United Nations Development Programme
– World Energy Assessment (2000)[4]

Thermal energy Main article: Solar thermal energy Solar thermal technologies can be used for water heating, space heating, space cooling and process heat generation.[20] Early commercial adaptation In 1878, at the Universal Exposition in Paris, Augustin Mouchot successfully demonstrated a solar steam engine, but couldn't continue development because of cheap coal and other factors.

1917 Patent drawing of Shuman's solar collector

In 1897, Frank Shuman, a U.S. inventor, engineer and solar energy pioneer, built a small demonstration solar engine that worked by reflecting solar energy onto square boxes filled with ether, which has a lower boiling point than water, and were fitted internally with black pipes which in turn powered a steam engine. In 1908 Shuman formed the Sun
Power Company with the intent of building larger solar power plants. He, along with his technical advisor A.S.E. Ackermann and British physicist Sir Charles Vernon Boys,[citation needed] developed an improved system using mirrors to reflect solar energy upon collector boxes, increasing heating capacity to the extent that water could now be used instead of ether. Shuman then constructed a full-scale steam engine powered by low-pressure water, enabling him to patent the entire solar engine system by 1912. Shuman built the world's first solar thermal power station in Maadi, Egypt, between 1912 and 1913. His plant used parabolic troughs to power a 45–52 kilowatts (60–70 hp) engine that pumped more than 22,000 litres (4,800 imp gal; 5,800 US gal) of water per minute from the Nile River
Nile River
to adjacent cotton fields. Although the outbreak of World War I and the discovery of cheap oil in the 1930s discouraged the advancement of solar energy, Shuman's vision and basic design were resurrected in the 1970s with a new wave of interest in solar thermal energy.[21] In 1916 Shuman was quoted in the media advocating solar energy's utilization, saying:

We have proved the commercial profit of sun power in the tropics and have more particularly proved that after our stores of oil and coal are exhausted the human race can receive unlimited power from the rays of the sun. — Frank Shuman, New York Times, 2 July 1916[22]

heating Main articles: Solar hot water
Solar hot water
and Solar combisystem

Solar water heaters facing the Sun
to maximize gain

Solar hot water
Solar hot water
systems use sunlight to heat water. In low geographical latitudes (below 40 degrees) from 60 to 70% of the domestic hot water use with temperatures up to 60 °C can be provided by solar heating systems.[23] The most common types of solar water heaters are evacuated tube collectors (44%) and glazed flat plate collectors (34%) generally used for domestic hot water; and unglazed plastic collectors (21%) used mainly to heat swimming pools.[24] As of 2007, the total installed capacity of solar hot water systems was approximately 154 thermal gigawatt (GWth).[25] China is the world leader in their deployment with 70  GWth
installed as of 2006 and a long-term goal of 210  GWth
by 2020.[26] Israel
and Cyprus
are the per capita leaders in the use of solar hot water systems with over 90% of homes using them.[27] In the United States, Canada, and Australia, heating swimming pools is the dominant application of solar hot water with an installed capacity of 18  GWth
as of 2005.[19] Heating, cooling and ventilation Main articles: Solar heating, Thermal mass, Solar chimney, and Solar air conditioning In the United States, heating, ventilation and air conditioning (HVAC) systems account for 30% (4.65 EJ/yr) of the energy used in commercial buildings and nearly 50% (10.1 EJ/yr) of the energy used in residential buildings.[28][29] Solar heating, cooling and ventilation technologies can be used to offset a portion of this energy.

MIT's Solar House #1, built in 1939 in the U.S., used seasonal thermal energy storage for year-round heating.

Thermal mass
Thermal mass
is any material that can be used to store heat—heat from the Sun
in the case of solar energy. Common thermal mass materials include stone, cement and water. Historically they have been used in arid climates or warm temperate regions to keep buildings cool by absorbing solar energy during the day and radiating stored heat to the cooler atmosphere at night. However, they can be used in cold temperate areas to maintain warmth as well. The size and placement of thermal mass depend on several factors such as climate, daylighting and shading conditions. When properly incorporated, thermal mass maintains space temperatures in a comfortable range and reduces the need for auxiliary heating and cooling equipment.[30] A solar chimney (or thermal chimney, in this context) is a passive solar ventilation system composed of a vertical shaft connecting the interior and exterior of a building. As the chimney warms, the air inside is heated causing an updraft that pulls air through the building. Performance can be improved by using glazing and thermal mass materials[31] in a way that mimics greenhouses. Deciduous
trees and plants have been promoted as a means of controlling solar heating and cooling. When planted on the southern side of a building in the northern hemisphere or the northern side in the southern hemisphere, their leaves provide shade during the summer, while the bare limbs allow light to pass during the winter.[32] Since bare, leafless trees shade 1/3 to 1/2 of incident solar radiation, there is a balance between the benefits of summer shading and the corresponding loss of winter heating.[33] In climates with significant heating loads, deciduous trees should not be planted on the Equator-facing side of a building because they will interfere with winter solar availability. They can, however, be used on the east and west sides to provide a degree of summer shading without appreciably affecting winter solar gain.[34] Cooking Main article: Solar cooker

Parabolic dish produces steam for cooking, in Auroville, India

Solar cookers use sunlight for cooking, drying and pasteurization. They can be grouped into three broad categories: box cookers, panel cookers and reflector cookers.[35] The simplest solar cooker is the box cooker first built by Horace de Saussure
Horace de Saussure
in 1767.[36] A basic box cooker consists of an insulated container with a transparent lid. It can be used effectively with partially overcast skies and will typically reach temperatures of 90–150 °C (194–302 °F).[37] Panel cookers use a reflective panel to direct sunlight onto an insulated container and reach temperatures comparable to box cookers. Reflector cookers use various concentrating geometries (dish, trough, Fresnel mirrors) to focus light on a cooking container. These cookers reach temperatures of 315 °C (599 °F) and above but require direct light to function properly and must be repositioned to track the Sun.[38] Process heat Main articles: Solar pond, Salt evaporation pond, and Solar furnace Solar concentrating technologies such as parabolic dish, trough and Scheffler reflectors can provide process heat for commercial and industrial applications. The first commercial system was the Solar Total Energy
Project (STEP) in Shenandoah, Georgia, USA where a field of 114 parabolic dishes provided 50% of the process heating, air conditioning and electrical requirements for a clothing factory. This grid-connected cogeneration system provided 400 kW of electricity plus thermal energy in the form of 401 kW steam and 468 kW chilled water, and had a one-hour peak load thermal storage.[39] Evaporation
ponds are shallow pools that concentrate dissolved solids through evaporation. The use of evaporation ponds to obtain salt from seawater is one of the oldest applications of solar energy. Modern uses include concentrating brine solutions used in leach mining and removing dissolved solids from waste streams.[40] Clothes lines, clotheshorses, and clothes racks dry clothes through evaporation by wind and sunlight without consuming electricity or gas. In some states of the United States legislation protects the "right to dry" clothes.[41] Unglazed transpired collectors (UTC) are perforated sun-facing walls used for preheating ventilation air. UTCs can raise the incoming air temperature up to 22 °C (40 °F) and deliver outlet temperatures of 45–60 °C (113–140 °F).[42] The short payback period of transpired collectors (3 to 12 years) makes them a more cost-effective alternative than glazed collection systems.[42] As of 2003, over 80 systems with a combined collector area of 35,000 square metres (380,000 sq ft) had been installed worldwide, including an 860 m2 (9,300 sq ft) collector in Costa Rica
Costa Rica
used for drying coffee beans and a 1,300 m2 (14,000 sq ft) collector in Coimbatore, India, used for drying marigolds.[43] Water
treatment Main articles: Solar still, Solar water disinfection, Solar desalination, and Solar Powered Desalination

Solar water disinfection
Solar water disinfection
in Indonesia

Solar distillation can be used to make saline or brackish water potable. The first recorded instance of this was by 16th-century Arab alchemists.[44] A large-scale solar distillation project was first constructed in 1872 in the Chilean mining town of Las Salinas.[45] The plant, which had solar collection area of 4,700 m2 (51,000 sq ft), could produce up to 22,700 L (5,000 imp gal; 6,000 US gal) per day and operate for 40 years.[45] Individual still designs include single-slope, double-slope (or greenhouse type), vertical, conical, inverted absorber, multi-wick, and multiple effect. These stills can operate in passive, active, or hybrid modes. Double-slope stills are the most economical for decentralized domestic purposes, while active multiple effect units are more suitable for large-scale applications.[44] Solar water disinfection
Solar water disinfection
(SODIS) involves exposing water-filled plastic polyethylene terephthalate (PET) bottles to sunlight for several hours.[46] Exposure times vary depending on weather and climate from a minimum of six hours to two days during fully overcast conditions.[47] It is recommended by the World Health Organization
World Health Organization
as a viable method for household water treatment and safe storage.[48] Over two million people in developing countries use this method for their daily drinking water.[47] Solar energy
Solar energy
may be used in a water stabilization pond to treat waste water without chemicals or electricity. A further environmental advantage is that algae grow in such ponds and consume carbon dioxide in photosynthesis, although algae may produce toxic chemicals that make the water unusable.[49][50] Molten salt
Molten salt
technology Molten salt
Molten salt
can be employed as a thermal energy storage method to retain thermal energy collected by a solar tower or solar trough of a concentrated solar power plant, so that it can be used to generate electricity in bad weather or at night. It was demonstrated in the Solar Two
Solar Two
project from 1995–1999. The system is predicted to have an annual efficiency of 99%, a reference to the energy retained by storing heat before turning it into electricity, versus converting heat directly into electricity.[51][52][53] The molten salt mixtures vary. The most extended mixture contains sodium nitrate, potassium nitrate and calcium nitrate. It is non-flammable and nontoxic, and has already been used in the chemical and metals industries as a heat-transport fluid, so experience with such systems exists in non-solar applications. The salt melts at 131 °C (268 °F). It is kept liquid at 288 °C (550 °F) in an insulated "cold" storage tank. The liquid salt is pumped through panels in a solar collector where the focused sun heats it to 566 °C (1,051 °F). It is then sent to a hot storage tank. This is so well insulated that the thermal energy can be usefully stored for up to a week.[54] When electricity is needed, the hot salt is pumped to a conventional steam-generator to produce superheated steam for a turbine/generator as used in any conventional coal, oil, or nuclear power plant. A 100-megawatt turbine would need a tank about 9.1 metres (30 ft) tall and 24 metres (79 ft) in diameter to drive it for four hours by this design. Several parabolic trough power plants in Spain[55] and solar power tower developer SolarReserve
use this thermal energy storage concept. The Solana Generating Station
Solana Generating Station
in the U.S. has six hours of storage by molten salt. The María Elena plant[56] is a 400 MW thermo-solar complex in the northern Chilean region of Antofagasta employing molten salt technology. Electricity
production Main article: Solar power

Some of the world's largest solar power stations: Ivanpah (CSP) and Topaz (PV)

Solar power
Solar power
is the conversion of sunlight into electricity, either directly using photovoltaics (PV), or indirectly using concentrated solar power (CSP). CSP systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. PV converts light into electric current using the photoelectric effect. Solar power
Solar power
is anticipated to become the world's largest source of electricity by 2050, with solar photovoltaics and concentrated solar power contributing 16 and 11 percent to the global overall consumption, respectively.[57] In 2016, after another year of rapid growth, solar generated 1.3% of global power.[58] Commercial concentrated solar power plants were first developed in the 1980s. The 392 MW Ivanpah Solar Power Facility, in the Mojave Desert of California, is the largest solar power plant in the world. Other large concentrated solar power plants include the 150 MW Solnova Solar Power Station and the 100 MW Andasol solar power station, both in Spain. The 250 MW Agua Caliente Solar Project, in the United States, and the 221 MW Charanka Solar Park in India, are the world's largest photovoltaic plants. Solar projects exceeding 1 GW are being developed, but most of the deployed photovoltaics are in small rooftop arrays of less than 5 kW, which are connected to the grid using net metering and/or a feed-in tariff.[59] Photovoltaics Main article: Photovoltaics








     Europe      Asia-Pacific      Americas      China      Middle East and Africa Worldwide growth of PV capacity grouped by region in MW (2006–2014)

In the last two decades, photovoltaics (PV), also known as solar PV, has evolved from a pure niche market of small scale applications towards becoming a mainstream electricity source. A solar cell is a device that converts light directly into electricity using the photoelectric effect. The first solar cell was constructed by Charles Fritts in the 1880s.[60] In 1931 a German engineer, Dr Bruno Lange, developed a photo cell using silver selenide in place of copper oxide.[61] Although the prototype selenium cells converted less than 1% of incident light into electricity, both Ernst Werner von Siemens and James Clerk Maxwell
James Clerk Maxwell
recognized the importance of this discovery.[62] Following the work of Russell Ohl in the 1940s, researchers Gerald Pearson, Calvin Fuller
Calvin Fuller
and Daryl Chapin created the crystalline silicon solar cell in 1954.[63] These early solar cells cost 286 USD/watt and reached efficiencies of 4.5–6%.[64] By 2012 available efficiencies exceeded 20%, and the maximum efficiency of research photovoltaics was in excess of 40%.[65] Concentrated solar power See also: Concentrated solar power Concentrating Solar Power (CSP) systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. The concentrated heat is then used as a heat source for a conventional power plant. A wide range of concentrating technologies exists; the most developed are the parabolic trough, the concentrating linear fresnel reflector, the Stirling dish and the solar power tower. Various techniques are used to track the Sun
and focus light. In all of these systems a working fluid is heated by the concentrated sunlight, and is then used for power generation or energy storage.[66] Architecture and urban planning Main articles: Passive solar building design
Passive solar building design
and Urban heat island

Darmstadt University of Technology, Germany, won the 2007 Solar Decathlon in Washington, D.C. with this passive house designed for humid and hot subtropical climate.[67]

has influenced building design since the beginning of architectural history.[68] Advanced solar architecture and urban planning methods were first employed by the Greeks and Chinese, who oriented their buildings toward the south to provide light and warmth.[69] The common features of passive solar architecture are orientation relative to the Sun, compact proportion (a low surface area to volume ratio), selective shading (overhangs) and thermal mass.[68] When these features are tailored to the local climate and environment they can produce well-lit spaces that stay in a comfortable temperature range. Socrates' Megaron House is a classic example of passive solar design.[68] The most recent approaches to solar design use computer modeling tying together solar lighting, heating and ventilation systems in an integrated solar design package.[70] Active solar equipment such as pumps, fans and switchable windows can complement passive design and improve system performance. Urban heat islands (UHI) are metropolitan areas with higher temperatures than that of the surrounding environment. The higher temperatures result from increased absorption of solar energy by urban materials such as asphalt and concrete, which have lower albedos and higher heat capacities than those in the natural environment. A straightforward method of counteracting the UHI effect is to paint buildings and roads white, and to plant trees in the area. Using these methods, a hypothetical "cool communities" program in Los Angeles has projected that urban temperatures could be reduced by approximately 3 °C at an estimated cost of US$1 billion, giving estimated total annual benefits of US$530 million from reduced air-conditioning costs and healthcare savings.[71] Agriculture
and horticulture

like these in the Westland municipality of the Netherlands grow vegetables, fruits and flowers.

and horticulture seek to optimize the capture of solar energy in order to optimize the productivity of plants. Techniques such as timed planting cycles, tailored row orientation, staggered heights between rows and the mixing of plant varieties can improve crop yields.[72][73] While sunlight is generally considered a plentiful resource, the exceptions highlight the importance of solar energy to agriculture. During the short growing seasons of the Little Ice
Age, French and English farmers employed fruit walls to maximize the collection of solar energy. These walls acted as thermal masses and accelerated ripening by keeping plants warm. Early fruit walls were built perpendicular to the ground and facing south, but over time, sloping walls were developed to make better use of sunlight. In 1699, Nicolas Fatio de Duillier
Nicolas Fatio de Duillier
even suggested using a tracking mechanism which could pivot to follow the Sun.[74] Applications of solar energy in agriculture aside from growing crops include pumping water, drying crops, brooding chicks and drying chicken manure.[43][75] More recently the technology has been embraced by vintners, who use the energy generated by solar panels to power grape presses.[76] Greenhouses
convert solar light to heat, enabling year-round production and the growth (in enclosed environments) of specialty crops and other plants not naturally suited to the local climate. Primitive greenhouses were first used during Roman times to produce cucumbers year-round for the Roman emperor Tiberius.[77] The first modern greenhouses were built in Europe in the 16th century to keep exotic plants brought back from explorations abroad.[78] Greenhouses remain an important part of horticulture today, and plastic transparent materials have also been used to similar effect in polytunnels and row covers. Transport Main articles: Solar vehicle, Solar-charged vehicle, Electric boat, and Solar balloon

Winner of the 2013 World Solar Challenge
World Solar Challenge
in Australia

Solar electric aircraft circumnavigating the globe in 2015

Development of a solar-powered car has been an engineering goal since the 1980s. The World Solar Challenge
World Solar Challenge
is a biannual solar-powered car race, where teams from universities and enterprises compete over 3,021 kilometres (1,877 mi) across central Australia from Darwin to Adelaide. In 1987, when it was founded, the winner's average speed was 67 kilometres per hour (42 mph) and by 2007 the winner's average speed had improved to 90.87 kilometres per hour (56.46 mph).[79] The North American Solar Challenge
North American Solar Challenge
and the planned South African Solar Challenge are comparable competitions that reflect an international interest in the engineering and development of solar powered vehicles.[80][81] Some vehicles use solar panels for auxiliary power, such as for air conditioning, to keep the interior cool, thus reducing fuel consumption.[82][83] In 1975, the first practical solar boat was constructed in England.[84] By 1995, passenger boats incorporating PV panels began appearing and are now used extensively.[85] In 1996, Kenichi Horie made the first solar-powered crossing of the Pacific Ocean, and the Sun21 catamaran made the first solar-powered crossing of the Atlantic Ocean in the winter of 2006–2007.[86] There were plans to circumnavigate the globe in 2010.[87] In 1974, the unmanned AstroFlight Sunrise airplane made the first solar flight. On 29 April 1979, the Solar Riser
Solar Riser
made the first flight in a solar-powered, fully controlled, man-carrying flying machine, reaching an altitude of 40 ft (12 m). In 1980, the Gossamer Penguin made the first piloted flights powered solely by photovoltaics. This was quickly followed by the Solar Challenger
Solar Challenger
which crossed the English Channel in July 1981. In 1990 Eric Scott Raymond in 21 hops flew from California to North Carolina using solar power.[88] Developments then turned back to unmanned aerial vehicles (UAV) with the Pathfinder (1997) and subsequent designs, culminating in the Helios which set the altitude record for a non-rocket-propelled aircraft at 29,524 metres (96,864 ft) in 2001.[89] The Zephyr, developed by BAE Systems, is the latest in a line of record-breaking solar aircraft, making a 54-hour flight in 2007, and month-long flights were envisioned by 2010.[90] As of 2016, Solar Impulse, an electric aircraft, is currently circumnavigating the globe. It is a single-seat plane powered by solar cells and capable of taking off under its own power. The design allows the aircraft to remain airborne for several days.[91] A solar balloon is a black balloon that is filled with ordinary air. As sunlight shines on the balloon, the air inside is heated and expands causing an upward buoyancy force, much like an artificially heated hot air balloon. Some solar balloons are large enough for human flight, but usage is generally limited to the toy market as the surface-area to payload-weight ratio is relatively high.[92] Fuel production

Concentrated solar panels are getting a power boost. Pacific Northwest National Laboratory (PNNL) will be testing a new concentrated solar power system – one that can help natural gas power plants reduce their fuel usage by up to 20 percent.

Main articles: Solar chemical, Solar fuel, and Artificial photosynthesis Solar chemical
Solar chemical
processes use solar energy to drive chemical reactions. These processes offset energy that would otherwise come from a fossil fuel source and can also convert solar energy into storable and transportable fuels. Solar induced chemical reactions can be divided into thermochemical or photochemical.[93] A variety of fuels can be produced by artificial photosynthesis.[94] The multielectron catalytic chemistry involved in making carbon-based fuels (such as methanol) from reduction of carbon dioxide is challenging; a feasible alternative is hydrogen production from protons, though use of water as the source of electrons (as plants do) requires mastering the multielectron oxidation of two water molecules to molecular oxygen.[95] Some have envisaged working solar fuel plants in coastal metropolitan areas by 2050 – the splitting of sea water providing hydrogen to be run through adjacent fuel-cell electric power plants and the pure water by-product going directly into the municipal water system.[96] Another vision involves all human structures covering the earth's surface (i.e., roads, vehicles and buildings) doing photosynthesis more efficiently than plants.[97] Hydrogen
production technologies have been a significant area of solar chemical research since the 1970s. Aside from electrolysis driven by photovoltaic or photochemical cells, several thermochemical processes have also been explored. One such route uses concentrators to split water into oxygen and hydrogen at high temperatures (2,300–2,600 °C or 4,200–4,700 °F).[98] Another approach uses the heat from solar concentrators to drive the steam reformation of natural gas thereby increasing the overall hydrogen yield compared to conventional reforming methods.[99] Thermochemical cycles characterized by the decomposition and regeneration of reactants present another avenue for hydrogen production. The Solzinc process under development at the Weizmann Institute of Science
Weizmann Institute of Science
uses a 1 MW solar furnace to decompose zinc oxide (ZnO) at temperatures above 1,200 °C (2,200 °F). This initial reaction produces pure zinc, which can subsequently be reacted with water to produce hydrogen.[100] Energy storage
Energy storage
methods Main articles: Energy
storage, Seasonal thermal energy storage, Phase change material, Grid energy storage, and V2G

Thermal energy storage. The Andasol CSP plant uses tanks of molten salt to store solar energy.

Thermal mass
Thermal mass
systems can store solar energy in the form of heat at domestically useful temperatures for daily or interseasonal durations. Thermal storage systems generally use readily available materials with high specific heat capacities such as water, earth and stone. Well-designed systems can lower peak demand, shift time-of-use to off-peak hours and reduce overall heating and cooling requirements.[101][102] Phase change materials such as paraffin wax and Glauber's salt are another thermal storage medium. These materials are inexpensive, readily available, and can deliver domestically useful temperatures (approximately 64 °C or 147 °F). The "Dover House" (in Dover, Massachusetts) was the first to use a Glauber's salt heating system, in 1948.[103] Solar energy
Solar energy
can also be stored at high temperatures using molten salts. Salts are an effective storage medium because they are low-cost, have a high specific heat capacity and can deliver heat at temperatures compatible with conventional power systems. The Solar Two
Solar Two
project used this method of energy storage, allowing it to store 1.44 terajoules (400,000 kWh) in its 68 m³ storage tank with an annual storage efficiency of about 99%.[104] Off-grid PV systems have traditionally used rechargeable batteries to store excess electricity. With grid-tied systems, excess electricity can be sent to the transmission grid, while standard grid electricity can be used to meet shortfalls. Net metering
Net metering
programs give household systems a credit for any electricity they deliver to the grid. This is handled by 'rolling back' the meter whenever the home produces more electricity than it consumes. If the net electricity use is below zero, the utility then rolls over the kilowatt hour credit to the next month.[105] Other approaches involve the use of two meters, to measure electricity consumed vs. electricity produced. This is less common due to the increased installation cost of the second meter. Most standard meters accurately measure in both directions, making a second meter unnecessary. Pumped-storage hydroelectricity
Pumped-storage hydroelectricity
stores energy in the form of water pumped when energy is available from a lower elevation reservoir to a higher elevation one. The energy is recovered when demand is high by releasing the water, with the pump becoming a hydroelectric power generator.[106] Development, deployment and economics

Participants in a workshop on sustainable development inspect solar panels at Monterrey Institute of Technology and Higher Education, Mexico City on top of a building on campus.

Further information: Deployment of solar power to energy grids See also: Cost of electricity by source
Cost of electricity by source
and Renewable energy
Renewable energy
by country Beginning with the surge in coal use which accompanied the Industrial Revolution, energy consumption has steadily transitioned from wood and biomass to fossil fuels. The early development of solar technologies starting in the 1860s was driven by an expectation that coal would soon become scarce. However, development of solar technologies stagnated in the early 20th century in the face of the increasing availability, economy, and utility of coal and petroleum.[107] The 1973 oil embargo and 1979 energy crisis
1979 energy crisis
caused a reorganization of energy policies around the world and brought renewed attention to developing solar technologies.[108][109] Deployment strategies focused on incentive programs such as the Federal Photovoltaic Utilization Program in the U.S. and the Sunshine Program in Japan. Other efforts included the formation of research facilities in the U.S. (SERI, now NREL), Japan (NEDO), and Germany (Fraunhofer Institute for Solar Energy
Systems ISE).[110] Commercial solar water heaters began appearing in the United States in the 1890s.[111] These systems saw increasing use until the 1920s but were gradually replaced by cheaper and more reliable heating fuels.[112] As with photovoltaics, solar water heating attracted renewed attention as a result of the oil crises in the 1970s but interest subsided in the 1980s due to falling petroleum prices. Development in the solar water heating sector progressed steadily throughout the 1990s and annual growth rates have averaged 20% since 1999.[25] Although generally underestimated, solar water heating and cooling is by far the most widely deployed solar technology with an estimated capacity of 154 GW as of 2007.[25] The International Energy Agency
International Energy Agency
has said that solar energy can make considerable contributions to solving some of the most urgent problems the world now faces:[1]

The development of affordable, inexhaustible and clean solar energy technologies will have huge longer-term benefits. It will increase countries’ energy security through reliance on an indigenous, inexhaustible and mostly import-independent resource, enhance sustainability, reduce pollution, lower the costs of mitigating climate change, and keep fossil fuel prices lower than otherwise. These advantages are global. Hence the additional costs of the incentives for early deployment should be considered learning investments; they must be wisely spent and need to be widely shared.[1]

In 2011, a report by the International Energy Agency
International Energy Agency
found that solar energy technologies such as photovoltaics, solar hot water and concentrated solar power could provide a third of the world's energy by 2060 if politicians commit to limiting climate change. The energy from the sun could play a key role in de-carbonizing the global economy alongside improvements in energy efficiency and imposing costs on greenhouse gas emitters. "The strength of solar is the incredible variety and flexibility of applications, from small scale to big scale".[113]

We have proved ... that after our stores of oil and coal are exhausted the human race can receive unlimited power from the rays of the sun. — Frank Shuman, New York Times, 2 July 1916[22]

ISO standards The International Organization for Standardization
International Organization for Standardization
has established several standards relating to solar energy equipment. For example, ISO 9050 relates to glass in building while ISO 10217 relates to the materials used in solar water heaters. See also

Renewable energy
Renewable energy
portal Sustainable development portal Energy
portal Technology portal

Airmass Artificial photosynthesis Community solar farm Copper in renewable energy Desertec Global dimming Greasestock Green electricity Heliostat List of conservation topics List of renewable energy organizations List of solar energy topics Photovoltaic system Renewable heat Renewable energy
Renewable energy
by country Soil
solarization Solar Decathlon Solar easement Solar energy
Solar energy
use in rural Africa Solar updraft tower Solar power
Solar power
satellite Solar tracker SolarEdge Timeline of solar cells


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External links

Wikimedia Commons
has media related to Solar energy.

"How do Photovoltaics
Work?". NASA.  Renewable Energy: Solar at Curlie (based on DMOZ) Solar Energy
Back in the Day – slideshow by Life
magazine U.S. Solar Farm Map (1 MW or Higher) Online Resources Database on Solar in Developing Countries Online resources and news from the nonprofit American Solar Energy Society "Journal article traces dramatic advances in solar efficiency". SPIE Newsroom. Retrieved 4 November 2015. 

v t e

Solar energy


The Sun Solar irradiance Active and passive solar energy

Solar power


Passive solar
Passive solar
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Photovoltaics and related topics

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Other applications

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building design

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Process heat

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See also

topics Solar power
Solar power
by country Renewable energy
Renewable energy

v t e

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Portals: Energy Renewable energy Sustainable development

v t e




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Quantum efficiency

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List of semiconductor materials Crystalline silicon
Crystalline silicon
(c-Si) Polycrystalline silicon
Polycrystalline silicon
(multi-Si) Monocrystalline silicon
Monocrystalline silicon
(mono-Si) Cadmium telluride Copper indium gallium selenide Amorphous silicon
Amorphous silicon


Growth of photovoltaics Timeline of solar cells

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Polymer solar cell Nanocrystal solar cell Organic solar cell Quantum dot solar cell Hybrid solar cell Plasmonic solar cell Carbon nanotubes in photovoltaics Dye-sensitized solar cell Cadmium telluride
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photovoltaics Copper indium gallium selenide
Copper indium gallium selenide
solar cells Printed solar panel Perovskite solar cell

System components

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System concepts

Perturb and observe method Incremental conductance method Constant voltage method Fill factor Concentrated photovoltaics Photovoltaic thermal hybrid solar collector Space-based solar power



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Solar cell
phone charger Solar notebook Solar-powered calculator Solar-powered fountain Solar-powered radio Solar-powered flashlight Solar-powered fan Solar street light Solar traffic light


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Air transport

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racing List of solar car teams Solar challenges World Solar Challenge American Solar Challenge Formula Sun
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Grid-connected photovoltaic power system List of photovoltaic power stations

Individual projects

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Category Commons

v t e

The Sun

Internal structure

Core Radiation zone Tachocline Convection



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Spectral class: G2V

v t e

Natural resources


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peak farmland

Degradation Law



habitat conservation



law sand

peak rights


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planning reserve


Biodiversity Bioprospecting Biosphere Bushfood Bushmeat Fisheries

law management

Food Forests

genetic resources law management



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conservation management



Types / location


storage and recovery

Drinking Fresh Groundwater

pollution recharge remediation

Hydrosphere Ice

bergs glacial polar

Irrigation Rain


Stormwater Surface water Wastewater



Desalination Floods Law Leaching Sanitation Conflict Conservation Peak water Pollution Privatization Quality Right Resources

management policy



enclosure global land tragedy of


ecological land

Ecosystem services Exploitation

overexploitation Earth Overshoot Day



Natural capital


Nature reserve Systems ecology Urban ecology Wilderness


Common-pool Conflict (perpetuation) Curse Depletion Extraction Nationalism Renewable / Non-renewable


and agronomy Energy Environment Fishing Forestry Mining Water Wetlands


agencies law management ministries organizations

Colleges Natural resources

Authority control

GND: 40