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 techniques include the use of photovoltaic systems, concentrated solar power and solar water heating to harness the energy. 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 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]

Neapolitan Sunset
The source of Earth's solar power: the Sun

Potential

Breakdown of the incoming solar energy
About half the incoming solar energy reaches the Earth's surface.
Solar land area
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.

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]
Biomass 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 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 and Tidal power, derive their energy either directly or indirectly from the Sun.

Active solar techniques use photovoltaics, concentrated solar power, solar thermal collectors, pumps, and fans to convert sunlight into useful outputs. 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 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 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
Note:
  • 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 – World Energy Assessment (2000)[4]

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.

US Patent 1240890.pdf
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, 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 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]

Water heating

Twice Cropped Zonnecollectoren
Solar water heaters facing the Sun to maximize gain

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

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.

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

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

Auroville Solar Bowl
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 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

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, US 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 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

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 (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 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 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 technology

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 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 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

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

IvanpahRunning
Topaz Solar Farm, California Valley

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 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

50,000
100,000
150,000
200,000
2006
2010
2014
Desc-i.svg
     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 recognized the importance of this discovery.[62] Following the work of Russell Ohl in the 1940s, researchers Gerald Pearson, 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

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

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

Sunlight 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

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

Agriculture 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 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

Nuna 7
Winner of the 2013 World Solar Challenge in Australia
Flea Hop HB-SIA - Solar Impulse
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 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 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 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 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

Photo of the Week- Boosting Solar Technology (8722948189)
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.

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 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 methods

12-05-08 AS1
Thermal energy storage. The Andasol CSP plant uses tanks of molten salt to store solar energy.

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 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 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 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 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

03242012Taller sostenibilidad lore060
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.

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 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 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 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 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

References

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Further reading

  • Agrafiotis, C.; et al. (2005). "Solar water splitting for hydrogen production with monolithic reactors". Solar Energy. 79 (4): 409–21. Bibcode:2005SoEn...79..409A. doi:10.1016/j.solener.2005.02.026.
  • Anderson, Lorraine; Palkovic, Rick (1994). Cooking with Sunshine (The Complete Guide to Solar Cuisine with 150 Easy Sun-Cooked Recipes). Marlowe & Company. ISBN 978-1-56924-300-8.
  • Balcomb, J. Douglas (1992). Passive Solar Buildings. Massachusetts Institute of Technology. ISBN 978-0-262-02341-2.
  • Bénard, C.; Gobin, D.; Gutierrez, M. (1981). "Experimental Results of a Latent-Heat Solar-Roof, Used for Breeding Chickens". Solar Energy. 26 (4): 347–59. Bibcode:1981SoEn...26..347B. doi:10.1016/0038-092X(81)90181-X.
  • Bolton, James (1977). Solar Power and Fuels. Academic Press, Inc. ISBN 978-0-12-112350-5.
  • Bradford, Travis (2006). Solar Revolution: The Economic Transformation of the Global Energy Industry. MIT Press. ISBN 978-0-262-02604-8.
  • Butti, Ken; Perlin, John (1981). A Golden Thread (2500 Years of Solar Architecture and Technology). Van Nostrand Reinhold. ISBN 978-0-442-24005-9.
  • Carr, Donald E. (1976). Energy & the Earth Machine. W.W. Norton & Co. ISBN 978-0-393-06407-0.
  • Daniels, Farrington (1964). Direct Use of the Sun's Energy. Ballantine Books. ISBN 978-0-345-25938-7.
  • Denzer, Anthony (2013). The Solar House: Pioneering Sustainable Design. Rizzoli. ISBN 978-0-8478-4005-2. Archived from the original on 2013-07-26.
  • Halacy, Daniel (1973). The Coming Age of Solar Energy. Harper and Row. ISBN 978-0-380-00233-7.
  • Hunt, V. Daniel (1979). Energy Dictionary. Van Nostrand Reinhold Co. ISBN 978-0-442-27395-8.
  • Karan, Kaul; et al. (2001). "Row Orientation Affects Fruit Yield in Field-Grown Okra". Journal of Sustainable Agriculture. 17 (2/3): 169–74. doi:10.1300/J064v17n02_14.
  • Leon, M.; Kumar, S. (2007). "Mathematical modeling and thermal performance analysis of unglazed transpired solar collectors". Solar Energy. 81 (1): 62–75. Bibcode:2007SoEn...81...62L. doi:10.1016/j.solener.2006.06.017.
  • Lieth, Helmut; Whittaker, Robert (1975). Primary Productivity of the Biosphere. Springer-Verlag1. ISBN 978-0-387-07083-4.
  • Martin, Christopher L.; Goswami, D. Yogi (2005). Solar Energy Pocket Reference. International Solar Energy Society. ISBN 978-0-9771282-0-4.
  • Mazria, Edward (1979). The Passive Solar Energy Book. Rondale Press. ISBN 978-0-87857-238-0.
  • Meier, Anton; et al. (2005). "Solar chemical reactor technology for industrial production of lime". Solar Energy. 80 (10): 1355–62. Bibcode:2006SoEn...80.1355M. doi:10.1016/j.solener.2005.05.017.
  • Mills, David (2004). "Advances in solar thermal electricity technology". Solar Energy. 76 (1–3): 19–31. Bibcode:2004SoEn...76...19M. doi:10.1016/S0038-092X(03)00102-6.
  • Müller, Reto; Steinfeld, A. (2007). "Band-approximated radiative heat transfer analysis of a solar chemical reactor for the thermal dissociation of zinc oxide". Solar Energy. 81 (10): 1285–94. Bibcode:2007SoEn...81.1285M. doi:10.1016/j.solener.2006.12.006.
  • Perlin, John (1999). From Space to Earth (The Story of Solar Electricity). Harvard University Press. ISBN 978-0-674-01013-0.
  • Bartlett, Robert (1998). Solution Mining: Leaching and Fluid Recovery of Materials. Routledge. ISBN 978-90-5699-633-8.
  • Scheer, Hermann (2002). The Solar Economy (Renewable Energy for a Sustainable Global Future). Earthscan Publications Ltd. ISBN 978-1-84407-075-6.
  • Schittich, Christian (2003). Solar Architecture (Strategies Visions Concepts). Architektur-Dokumentation GmbH & Co. KG. ISBN 978-3-7643-0747-9.
  • Smil, Vaclav (1991). General Energetics: Energy in the Biosphere and Civilization. Wiley. p. 369. ISBN 978-0-471-62905-4.
  • Smil, Vaclav (2003). Energy at the Crossroads: Global Perspectives and Uncertainties. MIT Press. p. 443. ISBN 978-0-262-19492-1.
  • Smil, Vaclav (2006). Energy at the Crossroads (PDF). Organisation for Economic Co-operation and Development. ISBN 978-0-262-19492-1. Retrieved 29 September 2007.
  • Tabor, H.Z.; Doron, B. (1990). "The Beith Ha'Arava 5 MW(e) Solar Pond Power Plant (SPPP) – Progress Report". Solar Energy. 45 (4): 247–53. Bibcode:1990SoEn...45..247T. doi:10.1016/0038-092X(90)90093-R.
  • Tiwari, G.N.; Singh, H.N.; Tripathi, R. (2003). "Present status of solar distillation" (PDF). Solar Energy. 75 (5): 367–73. Bibcode:2003SoEn...75..367T. doi:10.1016/j.solener.2003.07.005.
  • Tritt, T.; Böttner, H.; Chen, L. (2008). "Thermoelectrics: Direct Solar Thermal Energy Conversion". MRS Bulletin. 33 (4): 355–72. doi:10.1557/mrs2008.73.
  • Tzempelikos, Athanassios; Athienitis, Andreas K. (2007). "The impact of shading design and control on building cooling and lighting demand". Solar Energy. 81 (3): 369–82. Bibcode:2007SoEn...81..369T. doi:10.1016/j.solener.2006.06.015.
  • Vecchia, A.; et al. (1981). "Possibilities for the Application of Solar Energy in the European Community Agriculture". Solar Energy. 26 (6): 479–89. Bibcode:1981SoEn...26..479D. doi:10.1016/0038-092X(81)90158-4.
  • Yergin, Daniel (1991). The Prize: The Epic Quest for Oil, Money, and Power. Simon & Schuster. p. 885. ISBN 978-0-671-79932-8.
  • Zedtwitz, P.V.; et al. (2006). "Hydrogen production via the solar thermal decarbonization of fossil fuels". Solar Energy. 80 (10): 1333–37. Bibcode:2006SoEn...80.1333Z. doi:10.1016/j.solener.2005.06.007.

External links

Agency for Non-conventional Energy and Rural Technology

The Agency for Non-Conventional Energy and Rural Technology (ANERT) is a government agency in the Kerala, India. Its mission is gathering and disseminating knowledge about non-conventional energy, energy conservation, and rural technology. The agency was established in 1986 with its headquarters at Thiruvananthapuram.

American Solar Energy Society

The American Solar Energy Society (ASES) is an association of solar professionals and advocates in the United States. Founded in 1954, ASES is dedicated to inspiring an era of energy innovation and speeding the transition toward a sustainable energy economy. The nonprofit advances education, research and policy.

Based in Boulder, Colorado, ASES is the American affiliate of the International Solar Energy Society.

ASES publishes Solar Today magazine, organizes the National Solar Tour, produces the National Solar Energy Conference National Solar Conference and World Renewable Energy Forum 2012, and advocates for policies to promote the research, commercialization and deployment of renewable energy.

Concentrated solar power

Concentrated solar power (also called concentrating solar power, concentrated solar thermal, and CSP) systems generate solar power by using mirrors or lenses to concentrate a large area of sunlight onto a small area. Electricity is generated when the concentrated light is converted to heat (solar thermal energy), which drives a heat engine (usually a steam turbine) connected to an electrical power generator or powers a thermochemical reaction (experimental as of 2013).CSP had a world's total installed capacity of 4,815 MW in 2016, up from 354 MW in 2005. As of 2017, Spain accounted for almost half of the world's capacity, at 2,300 MW, making this country the world leader in CSP. The United States follows with 1,740 MW. Interest is also notable in North Africa and the Middle East, as well as India and China. The global market has been dominated by parabolic-trough plants, which accounted for 90% of CSP plants at one point. The largest CSP projects in the world are the Ivanpah Solar Power Facility (392 MW) in the United States (which uses solar power tower technology) and the Mojave Solar Project (354 MW) in the United States (which uses parabolic troughs).

In most cases, CSP technologies currently cannot compete on price with photovoltaic solar panels, which have experienced huge growth in recent years due to falling prices and much smaller operating costs. CSP generally needs large amount of direct solar radiation, and its energy generation falls dramatically with cloud cover. This is in contrast with photovoltaics, which can produce electricity also from diffuse radiation.However, an advantage of CSP over photovoltaic conversion is that as a thermal technology, a CSP plant can incorporate thermal energy storage, which stores energy either in the form of sensible heat, or as latent heat (for example, using molten salt), which enables these plants to continue to generate electricity whenever it is needed, whether day or night. This makes CSP a dispatchable form of solar. This is particularly valuable in places where there is already a high penetration of PV, such as California because an evening peak is being exacerbated as PV ramps down at sunset.

CSP has other uses than electricity. Researchers are increasingly investigating solar thermal reactors for the production of solar fuels, making solar a fully transportable form of energy in the future. These researchers use the solar heat of CSP as a catalyst for thermochemistry to break apart molecules of H2O, to create hydrogen (H2) from solar energy with no carbon emissions. By splitting both H2O and CO2, other much-used hydrocarbons – for example, the jet fuel used to fly commercial airplanes – could also be created with solar energy rather than from fossil fuels.In 2017, CSP represented less than 2% of worldwide installed capacity of solar electricity plants. However, in recent years falling prices of CSP plants are making this technology competitive with other base-load power plants using fossil and nuclear fuel even in high moisture and dusty atmosphere at sea level, such as the United Arab Emirates. Base-load CSP tariff in the extremely dry Atacama region of Chile reached below ¢5.0/kWh in 2017 auctions.

Crescent Dunes Solar Energy Project

The Crescent Dunes Solar Energy Project is a 110 megawatt (MW) net solar thermal power project with 1.1 gigawatt-hours of energy storage, located near Tonopah, about 190 miles (310 km) northwest of Las Vegas.

It is the first utility-scale concentrating solar power (CSP) plant with a central receiver tower and advanced molten salt energy storage technology from SolarReserve. The project, developed by SolarReserve and owned by Tonopah Solar Energy, LLC. was anticipated to cost less than $1 billion. EPC Contractor was ACS Cobra, which carried out the engineering design, procured the equipment and materials necessary, and then constructed and delivered the facility to Tonopah Solar Energy. Maximum energy output is estimated at 500 GW·h annually, though the highest producing year thus far, 2018, only attained 40% of that, resulting in a capacity factor of about 20%.

The project includes 10,347 heliostats that collect and focus the sun's thermal energy to heat molten salt flowing through an approximately 640-foot (200 m) tall solar power tower. The molten salt circulates from the tower to a storage tank, where it is then used to produce steam and generate electricity. Excess thermal energy is stored in the molten salt and can be used to generate power for up to ten hours, including during the evening hours and when direct sunlight is not available. The storage technology also eliminates the need for any backup fossil fuels, such as natural gas. Each heliostat is made up of 35 6×6 feet (1.8 m) mirror facets, yielding a heliostat overall usable area of 1,245 square feet (115.7 m2). Total solar field aperture adds up to 12,882,015 square feet (1,196,778 m2).

Under a power purchase agreement (PPA) between SolarReserve and NV Energy, all power generated by the Crescent Dunes project in the next 25 years will be sold to Nevada Power Company for $0.135 per kilowatt-hour.

In late September, 2011, Tonopah Solar Energy received a $737 million loan guarantee from the U.S. Department of Energy (DOE). The capital stack included $170,000,000 in EB-5 investment through SolarReserve/ACS Cobra partner CMB Regional Centers.Ground was broken on the project in September 2011.

Construction terminated at the end of 2013, followed by several months of testing the plant systems. Melting about 70,000,000 pounds (32,000,000 kg) of salt takes two months. Once melted, the salt stays melted for the life of the plant and gets cycled through the receiver for reheating.

The project entered commissioning phase in February 2014 following completion of construction.

It began operation in September 2015, but went off-line in October 2016 due to a leak in a molten salt tank.

It returned to operation in July 2017.

Global Solar Energy

Global Solar Energy is a US-based manufacturer of CIGS solar cells, a thin-film based photovoltaic technology, with manufacturing operations in Tucson, Arizona, United States, and Berlin, Germany. In 2013, it was bought by Chinese renewable energy company Hanergy.

McCoy Solar Energy Project

The McCoy Solar Energy Project is a 250 megawatt (MWAC) photovoltaic power plant near the city of Blythe in Riverside County, California.

It occupies about 2,300 acres of mostly public land in the Mojave Desert. The construction uses CdTe thin film panels from First Solar, and the output is being sold to Southern California Edison under a power purchase agreement.The project is located adjacent to the 235 MW Blythe Solar Energy Center, together forming a larger 485 MW complex. The 550MW Desert Sunlight Solar Farm is located approximately 40miles west in Riverside County.

Rice Solar Energy Project

The Rice Solar Energy Project was a 150 MW concentrating solar power facility project proposed for Rice Valley in the southern Mojave Desert, within Riverside County in southern California. It was put on indefinite hold in 2014.

Sandstone Solar Energy Project

The Sandstone Solar Energy Project was a up to 1,600 megawatt (MW) solar thermal power project with 16 gigawatt-hours of energy storage, planned just to the east of Tonopah, about 170 miles (270 km) northwest of Las Vegas. The project was about up to eight 200 MW solar towers with integrated molten salt energy storage technology. The project, developed by SolarReserve and owned by Sandstone Solar Energy, LLC. was anticipated to cost about $5 billion. Planned energy output is 5,600 GW·h per year.The project includes heliostats that collect and focus the sun's thermal energy to heat molten salt flowing through a solar power tower. The molten salt circulates from the tower to a storage tank, where it is then used to produce steam and generate electricity. Excess thermal energy is stored in the molten salt and can be used to generate power for up to ten hours, including during the evening hours and when direct sunlight is not available. The storage technology also eliminates the need for any backup fossil fuels, such as natural gas.

Estimated construction start was in 2022. Each tower was be constructed within a 24 month construction cycle, staggered 6 months, expecting about 5 and half years to complete.In March 2019, the U.S. Bureau of Land Management confirmed that Sandstone Solar Energy has withdrawn its application for a construction and operation right-of-way on federal land for this project.On 15 April 2019, Sandstone Solar Energy filed for withdrawal of the application for a permit to construct the solar plant and requested closure of the relevant docket (No.17-08003). The Commission acknowledged the filing and closed the docket the same day.

Sharp Solar

Sharp Solar, a subsidiary of Sharp Electronics, is a solar energy products company owned by Sharp Corporation and based in Osaka, Japan.

Solar Energy Industries Association

The Solar Energy Industries Association (SEIA), established in 1974, is a national non-profit trade association of the solar-energy industry in the United States.

SEIA is a 501(c)6 non-profit trade association. SEIA's sister organization, The Solar Foundation, a 501(c)3 non-profit charitable organization, oversees policy-driven research and develops education & outreach programs to promote the further development of solar energy in the U.S.The association supports the extension of a 30 percent federal solar investment tax credit for eight years.With the recent high flux of green jobs in the solar industry, SEIA maintains a resource for those looking for solar jobs. The Harvard Business Review claims that the solar industry could absorb all of the jobs lost to the coal industry as it shutters. Solar already employs more people than the entire US coal industry.

Solar power

Solar power is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV), indirectly using concentrated solar power, or a combination. Concentrated solar power systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. Photovoltaic cells convert light into an electric current using the photovoltaic effect.Photovoltaics were initially solely used as a source of electricity for small and medium-sized applications, from the calculator powered by a single solar cell to remote homes powered by an off-grid rooftop PV system. Commercial concentrated solar power plants were first developed in the 1980s. The 392 MW Ivanpah installation is the largest concentrating solar power plant in the world, located in the Mojave Desert of California.

As the cost of solar electricity has fallen, the number of grid-connected solar PV systems has grown into the millions and utility-scale photovoltaic power stations with hundreds of megawatts are being built. Solar PV is rapidly becoming an inexpensive, low-carbon technology to harness renewable energy from the Sun. The current largest photovoltaic power station in the world is the 850 MW Longyangxia Dam Solar Park, in Qinghai, China.

The International Energy Agency projected in 2014 that under its "high renewables" scenario, by 2050, solar photovoltaics and concentrated solar power would contribute about 16 and 11 percent, respectively, of the worldwide electricity consumption, and solar would be the world's largest source of electricity. Most solar installations would be in China and India. In 2017, solar power provided 1.7% of total worldwide electricity production, growing at 35% per annum. As of 2018, the unsubsidised levelised cost of electricity for utility scale solar power is around $43/MWh.

Solar power in Bulgaria

Solar power in Bulgaria has expanded by 100 megawatts (MW) in 2011. A 16.2 MW solar power plant in Zdravetz, Bulgaria was expected to be completed in June 2012. Power will be sold for $0.30/kWh in a fixed rate 20 year power purchase agreement.Since then, however, new installations have nearly come to a halt with only about 12 MW of additional capacity installed during 2013 and 2014.

Solar power in China

China is the world's largest market for both photovoltaics and solar thermal energy.

Since 2013 China has been the world's leading installer of solar photovoltaics (PV).

In 2015, China became the world's largest producer of photovoltaic power, narrowly surpassing Germany.

In 2017 China was the first country to pass 100 GW of cumulative installed PV capacity, and by the end of 2018, it had 174 GW of cumulative installed solar capacity. As of May 2018, China holds the record for largest operational solar project in its 1,547-MW project at Tengger.

The contribution to the total electric energy production remains modest as the average capacity factor of solar power plants is relatively low at 17% on average.

Of the 6,412 TWh electricity produced in China in 2017, 118.2 TWh was generated by solar power, equivalent to 1.84% of total electricity production.

The goal for 2050 is to reach 1,300 GW of solar capacity.

If this goal is to be reached it would be the source with the largest installed capacity in China.Solar water heating is also extensively implemented, with a total installed capacity of 290 GWth at the end of 2014, representing about 70% of world's total installed solar thermal capacity.

Solar power in Pakistan

Pakistan has some of the highest values of insolation in the world, with eight to nine hours of sunshine per day, ideal climatic conditions for solar power generation.

However, the country has been slow to adopt the technology.

The country has solar plants in Pakistani Kashmir, Punjab, Sindh and Balochistan.

Initiatives are under development by the International Renewable Energy Agency, the Japan International Cooperation Agency, Chinese companies, and Pakistani private sector energy companies.

The country aims to build the world's largest solar power park, the Quaid-e-Azam Solar Power Park (QASP) in the Cholistan Desert, Punjab, by 2017 with a 1 GW capacity.

A plant of this size would be enough to power around 320,000 homes.

Solar power in South Africa

Solar power in South Africa includes photovoltaics (PV) as well as concentrated solar power (CSP).

In 2016, South Africa had 1,329 MW of installed solar power capacity.

Installed capacity is expected to reach 8,400 MW by 2030.In 2014 several solar farms were commissioned, including the 96 MW Jasper Solar Energy Project, one of Africa's largest photovoltaic power stations providing enough solar power for 30,000 homes.

Solar power in the Netherlands

Solar power in the Netherlands has an installed capacity of around 2,040 megawatt (MW) of photovoltaics as of the end of 2016. Around 525 MW of new capacity was installed during 2016, the third highest figure in Europe for that year.In November 2014 SolaRoad, the world's first experimental solar cycle path, was opened in the village of Krommenie. The aim of the project is to test the practicality and cost efficiency of embedding solar panels into a cycle path. The idea is that the path, which is expected to generate 50 to 70 kWh/m² each year, can power anything from street lights or traffic lights to electric cars or houses. The developers of SolaRoad believe that up to 20% of the 140,000 km of road in the Netherlands could be used to harvest solar energy.

Solar power in the United States

Solar power in the United States includes utility-scale solar power plants as well as local distributed generation, mostly from rooftop photovoltaics.

As of the end of 2017, the United States had over 50 gigawatts (GW) of installed photovoltaic capacity. In the twelve months through December 2018, utility scale solar power generated 66.6 terawatt-hours (TWh), 1.66% of total U.S. electricity. During the same time period total solar generation, including estimated small scale Generation photovoltaic generation, was 96.1 TWh, 2.30% of total U.S. electricity. In terms of total cumulative installed capacity, by year end 2017 the United States ranked 2nd in the world behind China.

In 2016, 39% of all new electricity generation capacity in the country came from solar, more than any other source and ahead of natural gas (29%). By 2015, solar employment had overtaken oil and gas as well as coal employment in the United States. In 2016, more than 260,000 Americans were employed in the solar industry.The United States conducted much early research in photovoltaics and concentrated solar power.

It is among the top countries in the world in electricity generated by the Sun and several of the world's largest utility-scale installations are located in the desert Southwest. The oldest solar power plant in the world is the 354-megawatt (MW) SEGS thermal power plant, in California. The Ivanpah Solar Electric Generating System is a solar thermal power project in the California Mojave Desert, 40 miles (64 km) southwest of Las Vegas, with a gross capacity of 392 MW. The 280 MW Solana Generating Station is a solar power plant near Gila Bend, Arizona, about 70 miles (110 km) southwest of Phoenix, completed in 2013. When commissioned it was the largest parabolic trough plant in the world and the first U.S. solar plant with molten salt thermal energy storage.There are plans to build many other large solar plants in the United States. Many states have set individual renewable energy goals with solar power being included in various proportions. Hawaii plans 100% renewable-sourced electricity by 2045. Governor Jerry Brown has signed legislation requiring California's utilities to obtain 100 percent of their electricity from zero-carbon sources by the end of 2045 (including 60% renewable energy sources by 2030).

Space Coast Next Generation Solar Energy Center

The Space Coast Next Generation Solar Energy Center is a 10 megawatt (MW) solar photovoltaic (PV) facility at the Kennedy Space Center, Florida. Commissioned in April 2010, the center is the result of a partnership between NASA and Florida Power & Light. The facility has approximately 35,000 solar photovoltaic panels from SunPower covering an area of 60 acres. The facility provides slightly less than one percent of the power needed to keep Kennedy Space Center up and running.

A 1 MW solar photovoltaic array is also located at the Kennedy Space Center.

The Space Coast Next Generation Solar Energy Center was the second largest-scale solar facility in Florida, with the 25 MW DeSoto Next Generation Solar Energy Center being the largest, until the construction of the 75 MW Martin Next Generation Solar Energy Center.

Timeline of solar cells

In the 19th century, it was observed that the sunlight striking certain materials generates detectable electric current - the photoelectric effect. This discovery has laid the foundation of solar cells. Solar cells have gone on to be used in many applications. They have historically been used in situations where electrical power from the grid was unavailable.

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