For the academic journal, see Solar Energy (journal).
Outstanding solar potential compared to all other energy sources.
Solar energy is radiant light and heat from the sun harnessed using a range of ever-evolving technologies such as solar heating, solar photovoltaics, solar thermal electricity, solar architecture and artificial photosynthesis.[1][2]
Solar technologies are broadly characterized as either passive solar or active solar depending on the way they capture, convert and distribute solar energy. Active solar techniques include the use of photovoltaic panels and solar thermal collectors 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.
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 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]
Renewable energy
Biofuel
Biomass
Geothermal
Hydropower
Solar energy
Tidal power
Wave power
Wind power
Topics by country
v
t
e
Contents
1 Energy from the Sun
2 Early commercial adaption
3 Applications of solar technology
3.1 Architecture and urban planning
3.2 Agriculture and horticulture
3.3 Transport and reconnaissance
3.4 Solar thermal
3.4.1 Water heating
3.4.2 Heating, cooling and ventilation
3.4.3 Water treatment
3.4.4 Process heat
3.4.5 Cooking
3.5 Electricity production
3.5.1 Concentrated solar power
3.5.2 Photovoltaics
3.5.3 Others
3.6 Fuel production
4 Energy storage methods
5 Development, deployment and economics
6 ISO Standards
7 See also
8 Notes
9 References
10 External links
Energy from the Sun
Main articles: Insolation and Solar radiation
About half the incoming solar energy reaches the Earth’s surface.
The Earth receives 174 petawatts (PW) of incoming solar radiation (insolation) at the upper atmosphere.[3] 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.[4]
Earth’s land surface, oceans and atmosphere absorb solar radiation, and this raises their temperature. 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.[5] Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14 °C.[6] By photosynthesis green plants convert solar energy into chemical energy, which produces food, wood and the biomass from which fossil fuels are derived.[7]
Yearly Solar fluxes & Human Energy Consumption
Solar
3,850,000 EJ
[8]
Wind
2,250 EJ
[9]
Biomass potential
~200 EJ
[10]
Primary energy use (2010)
539 EJ
[11]
Electricity (2010)
~67 EJ
[12]
1 Exajoule (EJ) is 1018 Joules or 278 billion kilowatt-hours (kW·h).
The total solar energy absorbed by Earth’s atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year.[8] In 2002, this was more energy in one hour than the world used in one year.[13][14] Photosynthesis captures approximately 3,000 EJ per year in biomass.[15] The technical potential available from biomass is from 100–300 EJ/year.[10] 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,[16]
Solar energy can be harnessed at different levels around the world, mostly depending on distance from the equator.[17]
Early commercial adaption
A 1917 patent drawing for Shuman’s parabolic trough solar energy system
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,[18] 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. Shuman’s plant used parabolic troughs to power a 45-52 kilowatt (60-70 H.P.) engine that pumped more than 22,000 litres 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.[19] 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, July 2, 1916[20]
Applications of solar technology
Average insolation showing land area (small black dots) required to replace the world primary energy supply with solar electricity (18 TW is 568 Exajoule, EJ, per year). Insolation for most people is from 150 to 300 W/m2 or 3.5 to 7.0 kWh/m2/day.
Solar energy refers primarily to the use of solar radiation for practical ends. However, all renewable energies, other than geothermal and tidal, derive their energy from the sun.
Solar technologies are broadly characterized as either passive or active depending on the way they capture, convert and distribute sunlight. Active solar techniques use photovoltaic panels, 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.[21]
Architecture and urban planning
Main articles: Passive solar building design and Urban heat island
Darmstadt University of Technology in Germany won the 2007 Solar Decathlon in Washington, D.C. with this passive house designed specifically for the humid and hot subtropical climate.[22]
Sunlight has influenced building design since the beginning of architectural history.[23] 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.[24]
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.[23] 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.[23] The most recent approaches to solar design use computer modeling tying together solar lighting, heating and ventilation systems in an integrated solar design package.[25]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 are a result of increased absorption of the Solar light 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 plant trees. 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.[26]
Agriculture and horticulture
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.[27][28] 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.[29] Applications of solar energy in agriculture aside from growing crops include pumping water, drying crops, brooding chicks and drying chicken manure.[30][31] More recently the technology has been embraced by vinters, who use the energy generated by solar panels to power grape presses.[32]
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.[33] The first modern greenhouses were built in Europe in the 16th century to keep exotic plants brought back from explorations abroad.[34] 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 and reconnaissance
Main articles: Solar vehicle, Solar-charged vehicle, Electric boat and Solar balloon
Australia hosts the World Solar Challenge where solar cars like the Nuna3 race through a 3,021 km (1,877 mi) course from Darwin to Adelaide.
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).[35] 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.[36][37]
Some vehicles use solar panels for auxiliary power, such as for air conditioning, to keep the interior cool, thus reducing fuel consumption.[38][39]
In 1975, the first practical solar boat was constructed in England.[40] By 1995, passenger boats incorporating PV panels began appearing and are now used extensively.[41] 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.[42] There are plans to circumnavigate the globe in 2010.[43]
Helios UAV in solar powered flight.
In 1974, the unmanned AstroFlight Sunrise plane 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 feet (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.[44] 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.[45] 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 are envisioned by 2010.[46]
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.[47]
Solar thermal
Main article: Solar thermal energy
Solar thermal technologies can be used for water heating, space heating, space cooling and process heat generation.[48]
Water heating
Main articles: Solar hot water and Solar combisystem
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.[49] 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.[50]
As of 2007, the total installed capacity of solar hot water systems is approximately 154 GW.[51] China is the world leader in their deployment with 70 GW installed as of 2006 and a long term goal of 210 GW by 2020.[52]Israel and Cyprus are the per capita leaders in the use of solar hot water systems with over 90% of homes using them.[53] In the United States, Canada and Australia heating swimming pools is the dominant application of solar hot water with an installed capacity of 18 GW as of 2005.[21]
Heating, cooling and ventilation
Main articles: Solar heating, Thermal mass, Solar chimney and Solar air conditioning
Solar House #1 of Massachusetts Institute of Technology in the United States, built in 1939, used Seasonal thermal energy storage for year-round heating.
In the United States, heating, ventilation and air conditioning (HVAC) systems account for 30% (4.65 EJ) of the energy used in commercial buildings and nearly 50% (10.1 EJ) of the energy used in residential buildings.[54][55] Solar heating, cooling and ventilation technologies can be used to offset a portion of this energy.
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.[56]
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[57] 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.[58] 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.[59] 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.[60]
Water treatment
Main articles: Solar still, Solar water disinfection, Solar desalination and Solar Powered Desalination Unit
Solar water disinfection in Indonesia
Small scale solar powered sewerage treatment plant.
Solar distillation can be used to make saline or brackish water potable. The first recorded instance of this was by 16th-century Arab alchemists.[61] A large-scale solar distillation project was first constructed in 1872 in the Chilean mining town of Las Salinas.[62] The plant, which had solar collection area of 4,700 m2, could produce up to 22,700 L per day and operated for 40 years.[62] Individual still designs include single-slope, double-slope (or greenhouse type), vertical, conical, inverted absorber, multi-wick, and multiple effect.[61] 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.[61]
Solar water disinfection (SODIS) involves exposing water-filled plastic polyethylene terephthalate (PET) bottles to sunlight for several hours.[63] Exposure times vary depending on weather and climate from a minimum of six hours to two days during fully overcast conditions.[64] It is recommended by the World Health Organization as a viable method for household water treatment and safe storage.<a href="http: