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ContentsArticles Sunlight 1 Solar energy 8 Solar thermal energy 24 Solar thermal collector 41 Photovoltaics 50 Photovoltaic system 61 Active solar 72 Passive solar building design 73 Daylighting 86 Hybrid solar lighting 92 Daylight saving time 93 Concentrated solar power 112 Air mass (solar energy) 118 Thermal mass 124 Thermal energy storage 128 Solar water heating 131 Solar combisystem 151 Solar architecture 154 Solar chimney 154 Solar air conditioning 159 Solar water disinfection 164 Solar desalination 170 Solar Powered Desalination Unit 172 Solar cooker 173 Solar pond 184 Salt evaporation pond 186 Solar furnace 188 Solar power 190 Solar chemical 199 Solar vehicle 200 Solar balloon 207 Solar sail 211 Solar power by country 226 Solar lamp 236
Solar tracker 237 SolarEdge 248 Solar inverter 251 Soil solarization 256 Space-based solar power 257 Sustainable energy 272 Community solar farm 285 Urban heat island 288References Article Sources and Contributors 297 Image Sources, Licenses and Contributors 303Article Licenses License 309
Sunlight 1 Sunlight "Sunshine" redirects here. For natural lighting of interior spaces by admitting sunlight, see Daylighting. For solar energy available from sunlight, see Insolation. For other uses, see Sunlight (disambiguation) and Sunshine (disambiguation). Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun, particularly infrared, visible, and ultraviolet light. On Earth, sunlight is filtered through the Earths atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon. When the direct solar radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright light and radiant heat. When it is blocked by the clouds or reflects off of other objects, it is experienced as diffused light. The World Meteorological Organization uses the term "sunshine duration" to mean the cumulative time during which an area receives direct irradiance from the Sun of at least 120 watts per square meter. Sunlight may be recorded using a sunshine recorder, pyranometer or pyrheliometer. Sunlight takes about 8.3 minutes to reach the Earth. On average, it takes energy between 10,000 and 170,000 Sunlight shining through clouds, giving rise to crepuscular rays. years to leave the suns interior and then be emitted from the surface as light. Direct sunlight has a luminous efficacy of about 93 lumens per watt of radiant flux. Bright sunlight provides illuminance of approximately 100,000 lux or lumens per square meter at the Earths surface. Sunlight is a key factor in photosynthesis, a process vital for many living beings on Earth. Composition The spectrum of the Suns solar radiation is close to that of a black body with a temperature of about 5,800 K. The Sun emits EM radiation across most of the electromagnetic spectrum. Although the Sun produces Gamma rays as a result of the nuclear fusion process, these super high energy photons are converted to lower energy photons before they reach the Suns surface and are emitted out into space. As a result, the Sun doesnt give off any gamma rays. The Sun does, however, emit X-rays, ultraviolet, visible light, infrared, and even radio waves. When ultraviolet radiation is not absorbed by the atmosphere Solar irradiance spectrum above atmosphere and or other protective coating, it can cause damage to the skin known as at surface sunburn or trigger an adaptive change in human skin pigmentation.
Sunlight 2 The spectrum of electromagnetic radiation striking the Earths atmosphere spans a range of 100 nm to about 1 mm. This can be divided into five regions in increasing order of wavelengths: • Ultraviolet C or (UVC) range, which spans a range of 100 to 280 nm. The term ultraviolet refers to the fact that the radiation is at higher frequency than violet light (and, hence also invisible to the human eye). Owing to absorption by the atmosphere very little reaches the Earths surface (Lithosphere). This spectrum of radiation has germicidal properties, and is used in germicidal lamps. • Ultraviolet B or (UVB) range spans 280 to 315 nm. It is also greatly absorbed by the atmosphere, and along with UVC is responsible for the photochemical reaction leading to the production of the ozone layer. • Ultraviolet A or (UVA) spans 315 to 400 nm. It has been traditionally held as less damaging to the DNA, and hence used in tanning and PUVA therapy for psoriasis. • Visible range or light spans 380 to 780 nm. As the name suggests, it is this range that is visible to the naked eye. • Infrared range that spans 700 nm to 106 nm (1 mm). It is responsible for an important part of the electromagnetic radiation that reaches the Earth. It is also divided into three types on the basis of wavelength: • Infrared-A: 700 nm to 1,400 nm • Infrared-B: 1,400 nm to 3,000 nm • Infrared-C: 3,000 nm to 1 mm Calculation To calculate the amount of sunlight reaching the ground, both the elliptical orbit of the Earth and the attenuation by the Earths atmosphere have to be taken into account. The extraterrestrial solar illuminance (Eext), corrected for the elliptical orbit by using the day number of the year (dn), is given by where dn=1 on January 1; dn=2 on January 2; dn=32 on February 1, etc. In this formula dn-3 is used, because in modern times Earths perihelion, the closest approach to the Sun and therefore the maximum Eext occurs around January 3 each year. The value of 0.033412 is determined knowing that the ratio between the perihelion (0.98328989 AU) squared and the aphelion (1.01671033 AU) squared should be approximately 0.935338. The solar illuminance constant (Esc), is equal to 128×103 lx. The direct normal illuminance (Edn), corrected for the attenuating effects of the atmosphere is given by: where c is the atmospheric extinction coefficient and m is the relative optical airmass. Solar constant The solar constant, a measure of flux density, is the amount of incoming solar electromagnetic radiation per unit area that would be incident on a plane perpendicular to the rays, at a distance of one astronomical unit (AU) (roughly the mean distance from the Sun to the Earth). The "solar constant" includes all types of solar radiation, not just the visible light. Its average value was thought to be approximately 1.366 kW/m², varying slightly with solar activity, but recent recalibrations of the relevant satellite observations indicate a value closer to 1.361 kW/m² is more realistic.
Sunlight 3 Total (TSI) and spectral solar irradiance (SSI) upon Earth Total Solar Irradiance upon Earth (TSI) was earlier measured by satellite to be roughly 1.366 kilowatts per square meter (kW/m²), but most recently NASA cites TSI as "1361 W/m² as compared to ~1366 W/m² from earlier observations [Kopp et al., 2005]", based on regular readings from NASAs Solar Radiation and Climate Experiment(SORCE) satellite, active since 2003, noting that this "discovery is critical in examining the energy budget of the planet Earth and isolating the climate change due to human activities." Furthermore the Spectral Irradiance Monitor (SIM) has found in the same period that spectral solar irradiance (SSI) at UV (ultraviolet) wavelength corresponds in a less clear, and probably more complicated fashion, with earths climate responses than earlier assumed, fueling broad avenues of new research in "the connection of the Sun and stratosphere, troposphere, biosphere, ocean, and Earth’s climate". Intensity in the Solar System Different bodies of the Solar System receive light of an intensity inversely proportional to the square of their distance from Sun. A rough table comparing the amount of solar radiation received by each planet in the Solar System follows (from data in ): Planet Perihelion - Solar radiation Aphelion maximum and distance (AU) minimum (W/m²) Mercury 0.3075 – 0.4667 14,446 – 6,272 Venus 0.7184 – 0.7282 2,647 – 2,576 Earth 0.9833 – 1.017 1,413 – 1,321 Mars 1.382 – 1.666 715 – 492 Jupiter 4.950 – 5.458 55.8 – 45.9 Saturn 9.048 – 10.12 16.7 – 13.4 Uranus 18.38 – 20.08 4.04 – 3.39 Neptune 29.77 – 30.44 1.54 – 1.47 The actual brightness of sunlight that would be observed at the surface depends also on the presence and composition of an atmosphere. For example Venus thick atmosphere reflects more than 60% of the solar light it receives. The actual illumination of the surface is about 14,000 lux, comparable to that on Earth "in the daytime with overcast clouds". Sunlight on Mars would be more or less like daylight on Earth wearing sunglasses, and as can be seen in the pictures taken by the rovers, there is enough diffuse sky radiation that shadows would not seem particularly dark. Thus it would give perceptions and "feel" very much like Earth daylight. For comparison purposes, sunlight on Saturn is slightly brighter than Earth sunlight at the average sunset or sunrise (see daylight for comparison table). Even on Pluto the sunlight would still be bright enough to almost match the average living room. To see sunlight as dim as full moonlight on the Earth, a distance of about 500 AU (~69 light-hours) is needed; there are only a handful of objects in the solar system known to orbit farther than such a distance, among them 90377 Sedna and (87269) 2000 OO67.
Sunlight 4 Surface illumination The spectrum of surface illumination depends upon solar elevation due to atmospheric effects, with the blue spectral component from atmospheric scatter dominating during twilight before and after sunrise and sunset, respectively, and red dominating during sunrise and sunset. These effects are apparent in natural light photography where the principal source of illumination is sunlight as mediated by the atmosphere. According to Craig Bohren, "preferential absorption of sunlight by ozone over long horizon paths gives the zenith sky its blueness when the sun is near the horizon". See diffuse sky radiation for more details. Climate effects Further information: Solar variation, Solar dimming, and Insolation On Earth, solar radiation is obvious as daylight when the sun is above the horizon. This is during daytime, and also in summer near the poles at night, but not at all in winter near the poles. When the direct radiation is not blocked by clouds, it is experienced as sunshine, combining the perception of bright white light (sunlight in the strict sense) and warming. The warming on the body, the ground and other objects depends on the absorption (electromagnetic radiation) of the electromagnetic radiation in the form of heat. The amount of radiation intercepted by a planetary body varies inversely with the square of the distance between the star and the planet. The Earths orbit and obliquity change with time (over thousands of years), sometimes forming a nearly perfect circle, and at other times stretching out to an orbital eccentricity of 5% (currently 1.67%). The total insolation remains almost constant due to Keplers second law, where is the "areal velocity" invariant. That is, the integration over the orbital period (also invariant) is a constant. If we assume the solar radiation power as a constant over time and the solar irradiation given by the inverse-square law, we obtain also the average insolation as a constant. But the seasonal and latitudinal distribution and intensity of solar radiation received at the Earths surface also varies. For example, at latitudes of 65 degrees the change in solar energy in summer & winter can vary by more than 25% as a result of the Earths orbital variation. Because changes in winter and summer tend to offset, the change in the annual average insolation at any given location is near zero, but the redistribution of energy between summer and winter does strongly affect the intensity of seasonal cycles. Such changes associated with the redistribution of solar energy are considered a likely cause for the coming and going of recent ice ages (see: Milankovitch cycles). Past variations in solar irradiance Space-based observations of solar irradiance started in 1978. These measurements show that the solar constant is not constant. It varies with the 11-year sunspot solar cycle. When going further back in time, one has to rely on irradiance reconstructions, using sunspots for the past 400 years or cosmogenic radionuclides for going back 10,000 years. Such reconstructions have been done . These studies show that solar irradiance does vary with distinct periodicities such as: 11 years (Schwabe), 88 years (Gleisberg cycle), 208 years (DeVries cycle) and 1,000 years (Eddy cycle).
Sunlight 5 Life on Earth The existence of nearly all life on Earth is fueled by light from the sun. Most autotrophs, such as plants, use the energy of sunlight, combined with carbon dioxide and water, to produce simple sugars—a process known as photosynthesis. These sugars are then used as building blocks and in other synthetic pathways which allow the organism to grow. Heterotrophs, such as animals, use light from the sun indirectly by consuming the products of autotrophs, either by consuming autotrophs, by consuming their products or by consuming other heterotrophs. The This short film explores the vital connection sugars and other molecular components produced by the autotrophs are between Earth and the Sun. then broken down, releasing stored solar energy, and giving the heterotroph the energy required for survival. This process is known as cellular respiration. In prehistory, humans began to further extend this process by putting plant and animal materials to other uses. They used animal skins for warmth, for example, or wooden weapons to hunt. These skills allowed humans to harvest more of the sunlight than was possible through glycolysis alone, and human population began to grow. During the Neolithic Revolution, the domestication of plants and animals further increased human access to solar energy. Fields devoted to crops were enriched by inedible plant matter, providing sugars and nutrients for future harvests. Animals which had previously only provided humans with meat and tools once they were killed were now used for labour throughout their lives, fueled by grasses inedible to humans. The more recent discoveries of coal, petroleum and natural gas are modern extensions of this trend. These fossil fuels are the remnants of ancient plant and animal matter, formed using energy from sunlight and then trapped within the earth for millions of years. Because the stored energy in these fossil fuels has accumulated over many millions of years, they have allowed modern humans to massively increase the production and consumption of primary energy. As the amount of fossil fuel is large but finite, this cannot continue indefinitely, and various theories exist as to what will follow this stage of human civilization (e.g. alternative fuels, Malthusian catastrophe, new urbanism, peak oil). Cultural aspects The effect of sunlight is relevant to painting, evidenced for instance in works of Claude Monet on outdoor scenes and landscapes. Many people find direct sunlight to be too bright for comfort, especially when reading from white paper upon which the sun is directly shining. Indeed, looking directly at the sun can cause long-term vision damage. To compensate for the brightness of sunlight, many people wear sunglasses. Cars, many helmets and caps are equipped with visors to block the sun from direct vision when the sun is at a low angle. Sunshine is often blocked from entering buildings through the use of walls, window blinds, awnings, shutters or curtains, or by nearby shade trees. In colder countries, many people prefer sunnier days and often avoid the shade. In hotter countries the converse is true; during the midday Claude Monet: Le déjeuner sur lherbe hours many people prefer to stay inside to remain cool. If they do go outside, they seek shade which may be provided by trees, parasols, and so on.
Sunlight 6 In Hinduism the sun is considered to be a god as it is the source of life and energy on earth. Sunbathing Sunbathing is a popular leisure activity in which a person sits or lies in direct sunshine. People often sunbathe in comfortable places where there is ample sunlight. Some common places for sunbathing include beaches, open air swimming pools, parks, gardens, and sidewalk cafés. Sunbathers typically wear limited amounts of clothing or some simply go nude. For some, an alternative to sunbathing is the use of a sunbed that generates ultraviolet light and can be used indoors regardless of outdoor weather conditions and amount of sunlight. For many people with pale or brownish skin, one purpose for sunbathing is to darken ones skin color (get a sun tan) as this is considered in some cultures to be beautiful, associated with outdoor activity, vacations/holidays, and health. Some people prefer naked sunbathing so that an "all-over" or "even" tan can be obtained, sometimes as part of a specific lifestyle. For people suffering from psoriasis, sunbathing is an effective way of healing the symptoms. Skin tanning is achieved by an increase in the dark pigment inside skin cells called melanocytes and it is actually an automatic response mechanism of the body to sufficient exposure to ultraviolet radiation from the sun or from artificial sunlamps. Thus, the tan gradually disappears with time, when one is no longer exposed to these sources. Effects on human health The body produces vitamin D from sunlight (specifically from the UVB band of ultraviolet light), and excessive seclusion from the sun can lead to deficiency unless adequate amounts are obtained through diet. Sunburn can have mild to severe inflammation effects on skin; this can be avoided by using a proper sunscreen cream or lotion or by gradually building up melanocytes with increasing exposure. Another detrimental effect of UV exposure is accelerated skin aging (also called skin photodamage), which produces a difficult to treat cosmetic effect. Some people are concerned that ozone depletion is increasing the incidence of such health hazards. A 10% decrease in ozone could cause a 25% increase in skin cancer. A lack of sunlight, on the other hand, is considered one of the primary causes of seasonal affective disorder (SAD), a serious form of the "winter blues". SAD occurrence is more prevalent in locations further from the tropics, and most of the treatments (other than prescription drugs) involve light therapy, replicating sunlight via lamps tuned to specific (visible, not ultra-violet) wavelengths of light or full-spectrum bulbs. A recent study indicates that more exposure to sunshine early in a person’s life relates to less risk from multiple sclerosis (MS) later in life. References  "Chapter 8 – Measurement of sunshine duration" (http:/ / www. wmo. int/ pages/ prog/ www/ IMOP/ publications/ CIMO-Guide/ CIMO Guide 7th Edition, 2008/ Part I/ Chapter 8. pdf) (PDF). CIMO Guide. World Meteorological Organization. . Retrieved 2008-12-01.  "NASA: The 8-minute travel time to Earth by sunlight hides a thousand-year journey that actually began in the core" (http:/ / sunearthday. nasa. gov/ 2007/ locations/ ttt_sunlight. php). NASA, sunearthday.nasa.gov. . Retrieved 2012-02-12.  NASA Solar System Exploration - Sun: Facts & Figures (http:/ / solarsystem. nasa. gov/ planets/ profile. cfm?Display=Facts& Object=Sun) retrieved 27 April 2011 "Effective Temperature ... 5777 K"  "The Multispectral Sun, from the National Earth Science Teachers Association" (http:/ / www. windows2universe. org/ sun/ spectrum/ multispectral_sun_overview. html). Windows2universe.org. 2007-04-18. . Retrieved 2012-02-12.  Naylor, Mark; Kevin C. Farmer (1995). "Sun damage and prevention" (http:/ / www. telemedicine. org/ sundam/ sundam2. 4. 1. html). Electronic Textbook of Dermatology. The Internet Dermatology Society. . Retrieved 2008-06-02.  C. KANDILLI and K. ULGEN. "Solar Illumination and Estimating Daylight Availability of Global Solar Irradiance". Energy Sources.  "Satellite observations of total solar irradiance" (http:/ / acrim. com/ TSI Monitoring. htm). Acrim.com. . Retrieved 2012-02-12.  G. Kopp; J. Lean (2011). "A new, lower value of total solar irradiance: Evidence and climate significance". Geophys. Res. Lett.: L01706. Bibcode 2011GeoRL..3801706K. doi:10.1029/2010GL045777.
Sunlight 7  Willson, R. C., and A. V. Mordvinov (2003), Secular total solar irradiance trend during solar cycles 21–23, Geophys. Res. Lett., 30(5), 1199, doi:10.1029/2002GL016038 ACR (http:/ / www. acrim. com/ Reference Files/ Secular total solar irradiance trend during solar cycles 21â23. pdf)  "Construction of a Composite Total Solar Irradiance (TSI) Time Series from 1978 to present" (http:/ / www. pmodwrc. ch/ pmod. php?topic=tsi/ composite/ SolarConstant). . Retrieved 2005-10-05.  "NASA Goddard Space Flight Center: Solar Radiation" (http:/ / atmospheres. gsfc. nasa. gov/ climate/ index. php?section=136). Atmospheres.gsfc.nasa.gov. 2012-02-08. . Retrieved 2012-02-12.  http:/ / starhop. com/ library/ pdf/ studyguide/ high/ SolInt-19. pdf  "The Unveiling of Venus: Hot and Stifling". Science News 109 (25): 388. 1976-06-19. JSTOR 3960800. "100 watts per square meter ... 14,000 lux ... corresponds to ... daytime with overcast clouds"  Craig F. Bohren. "Atmospheric Optics" (http:/ / homepages. wmich. edu/ ~korista/ atmospheric_optics. pdf). .  "Graph of variation of seasonal and latitudinal distribution of solar radiation" (http:/ / www. museum. state. il. us/ exhibits/ ice_ages/ insolation_graph. html). Museum.state.il.us. 2007-08-30. . Retrieved 2012-02-12.  Wang et al. (2005). The Astrophysical Journal, Volume 625, issue 1, pages 522-538, dx.doi.org/10.1086/429689 (http:/ / dx. doi. org/ 10. 1086/ 429689).  Steinhilber et al. (2009), Geophysical Research Letters, Volume 36, L19704, http:/ / dx. doi. org/ 10. 1051/ 0004-6361/ 200811446  Vieira et al. (2011), Astronomy&Astrophysics, Volume 531, A6, http:/ / dx. doi. org/ 10. 1051/ 0004-6361/ 201015843  Steinhilber et al.(2012), Proceedings of the National Academy of Sciences, Early Edition http:/ / dx. doi. org/ 10. 1073/ pnas. 1118965109  Ozone Hole Consequences (http:/ / www. theozonehole. com/ consequences. htm) retrieved 30 October 2008  "NEUROLOGY 2007;69:381-388" (http:/ / www. neurology. org/ cgi/ content/ abstract/ 69/ 4/ 381?etoc). Neurology.org. 2007-07-24. . Retrieved 2012-02-12. Further reading • Hartmann, Thom (1998). The Last Hours of Ancient Sunlight. London: Hodder and Stoughton. ISBN 0-340-82243-0. External links • Solar radiation - Encyclopedia of Earth (http://www.eoearth.org/article/Solar_radiation) • Total Solar Irradiance (TSI) Daily mean data (http://www.ngdc.noaa.gov/stp/solar/solarirrad.html) at the website of the National Geophysical Data Center • Construction of a Composite Total Solar Irradiance (TSI) Time Series from 1978 to present (http://www. pmodwrc.ch/pmod.php?topic=tsi/composite/SolarConstant) by World Radiation Center, Physikalisch-Meteorologisches Observatorium Davos (pmod wrc) • A Comparison of Methods for Providing Solar Radiation Data to Crop Models and Decision Support Systems (http://www.macaulay.ac.uk/LADSS/papers.html?2002), Rivington et al. • Evaluation of three model estimations of solar radiation at 24 UK stations (http://www.macaulay.ac.uk/ LADSS/papers.html?2005), Rivington et al. • High resolution spectrum of solar radiation (http://bass2000.obspm.fr/solar_spect.php) from Observatoire de Paris • Measuring Solar Radiation (http://avc.comm.nsdlib.org/cgi-bin/wiki_grade_interface. pl?Measuring_Solar_Radiation) : A lesson plan from the National Science Digital Library. • Websurf astronomical information (http://websurf.nao.rl.ac.uk/surfbin/first.cgi): Online tools for calculating Rising and setting times of Sun, Moon or planet, Azimuth of Sun, Moon or planet at rising and setting, Altitude and azimuth of Sun, Moon or planet for a given date or range of dates, and more. • An Excel workbook (http://www.ecy.wa.gov/programs/eap/models/solrad.zip) with a solar position and solar radiation time-series calculator; by Greg Pelletier (http://www.ecy.wa.gov/programs/eap/models.html) • DOE information (http://rredc.nrel.gov/solar/spectra/am1.5/) about the ASTM standard solar spectrum for PV evaluation. • ASTM Standard (http://www.astm.org/Standards/G173.htm) for solar spectrum at ground level in the US (latitude ~ 37 degrees).
Sunlight 8 • Detailed spectrum of the sun (http://apod.nasa.gov/apod/ap100627.html) at Astronomy Picture of the Day (http://apod.nasa.gov/apod/archivepix.html). Solar energy Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar energy technologies include solar heating, solar photovoltaics, solar thermal electricity and solar architecture, which can make considerable contributions to solving some of the most urgent problems the world now faces. 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 Nellis Solar Power Plant in the United States, one of the largest photovoltaic power panels and solar thermal collectors to plants in North America. 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". Energy from the Sun The Earth receives 174 petawatts (PW) of incoming solar radiation (insolation) at the upper atmosphere. 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 Earths surface is mostly spread across the visible and near-infrared ranges with a small part in the near-ultraviolet. Earths 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. About half the incoming solar energy reaches the When the air reaches a high altitude, where the temperature is low, Earths surface.
Solar energy 9 water vapor condenses into clouds, which rain onto the Earths surface, completing the water cycle. The latent heat of water condensation amplifies convection, producing atmospheric phenomena such as wind, cyclones and anti-cyclones. Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14 °C. By photosynthesis green plants convert solar energy into chemical energy, which produces food, wood and the biomass from which fossil fuels are derived. Yearly Solar fluxes & Human Energy Consumption Solar  3,850,000 EJ Wind  2,250 EJ Biomass  3,000 EJ Primary energy use (2005)  487 EJ Electricity (2005)  56.7 EJ The total solar energy absorbed by Earths atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year. In 2002, this was more energy in one hour than the world used in one year. Photosynthesis captures approximately 3,000 EJ per year in biomass. 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 Earths non-renewable resources of coal, oil, natural gas, and mined uranium combined. Solar energy can be harnessed in different levels around the world. Depending on a geographical location the closer to the equator the more "potential" solar energy is available. Applications of solar technology 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 Average insolation showing land area (small black dots) required to replace the world primary the Sun. Active solar technologies increase the supply of energy and energy supply with solar electricity. 18 TW is are considered supply side technologies, while passive solar 568 Exajoule (EJ) per year. Insolation for most technologies reduce the need for alternate resources and are generally people is from 150 to 300 W/m2 or 3.5 to 7.0 considered demand side technologies. kWh/m2/day.
Solar energy 10 Architecture and urban planning Sunlight has influenced building design since the beginning of architectural history. 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. 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. When these Darmstadt University of Technology in Germany features are tailored to the local climate and environment they can won the 2007 Solar Decathlon in Washington, produce well-lit spaces that stay in a comfortable temperature range. D.C. with this passive house designed specifically  Socrates Megaron House is a classic example of passive solar for the humid and hot subtropical climate. design. The most recent approaches to solar design use computer modeling tying together solar lighting, heating and ventilation systems in an integrated solar design package. 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. Agriculture and horticulture 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. While sunlight is generally considered a plentiful Greenhouses like these in the Westland municipality of the Netherlands grow vegetables, resource, the exceptions highlight the importance of solar energy to fruits and flowers. 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. Applications of solar energy in agriculture aside from growing crops include pumping water, drying crops, brooding chicks and drying chicken manure. More recently the technology has been embraced by vinters, who use the energy generated by solar panels to power grape presses. 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. The first modern greenhouses were built in Europe in the 16th century to keep exotic plants brought back from explorations abroad. Greenhouses remain an important part of horticulture today, and plastic transparent materials have also been used to similar effect in polytunnels and row covers.
Solar energy 11 Solar lighting The history of lighting is dominated by the use of natural light. The Romans recognized a right to light as early as the 6th century and English law echoed these judgments with the Prescription Act of 1832. In the 20th century artificial lighting became the main source of interior illumination but daylighting techniques and hybrid solar lighting solutions are ways to reduce energy consumption. Daylighting systems collect and distribute sunlight to provide interior illumination. This passive technology directly offsets energy use by replacing artificial lighting, and indirectly offsets non-solar energy use Daylighting features such as this oculus at the top by reducing the need for air-conditioning. Although difficult to of the Pantheon, in Rome, Italy have been in use quantify, the use of natural lighting also offers physiological and since antiquity.  psychological benefits compared to artificial lighting. Daylighting design implies careful selection of window types, sizes and orientation; exterior shading devices may be considered as well. Individual features include sawtooth roofs, clerestory windows, light shelves, skylights and light tubes. They may be incorporated into existing structures, but are most effective when integrated into a solar design package that accounts for factors such as glare, heat flux and time-of-use. When daylighting features are properly implemented they can reduce lighting-related energy requirements by 25%. Hybrid solar lighting is an active solar method of providing interior illumination. HSL systems collect sunlight using focusing mirrors that track the Sun and use optical fibers to transmit it inside the building to supplement conventional lighting. In single-story applications these systems are able to transmit 50% of the direct sunlight received. Solar lights that charge during the day and light up at dusk are a common sight along walkways. Solar-charged lanterns have become popular in developing countries where they provide a safer and cheaper alternative to kerosene lamps. Although daylight saving time is promoted as a way to use sunlight to save energy, recent research has been limited and reports contradictory results: several studies report savings, but just as many suggest no effect or even a net loss, particularly when gasoline consumption is taken into account. Electricity use is greatly affected by geography, climate and economics, making it hard to generalize from single studies.
Solar energy 12 Solar thermal Solar thermal technologies can be used for water heating, space heating, space cooling and process heat generation. Water heating 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. 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. As of 2007, the total installed capacity of solar hot water systems is approximately 154 GW. 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. Israel and Cyprus are the per capita leaders in the use of solar hot water systems with over 90% of homes using them. Solar water heaters facing the Sun to maximize In the United States, Canada and Australia heating swimming pools is gain. the dominant application of solar hot water with an installed capacity of 18 GW as of 2005. Heating, cooling and ventilation 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. 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 Solar House #1 of Massachusetts Institute of absorbing solar energy during the day and radiating stored heat to the Technology in the United States, built in 1939, cooler atmosphere at night. However they can be used in cold used seasonal thermal storage for year-round temperate areas to maintain warmth as well. The size and placement of heating. 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. 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 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, their leaves provide shade during the summer, while the bare limbs allow light to pass during the winter. 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. In climates with significant
Solar energy 13 heating loads, deciduous trees should not be planted on the southern 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. 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. A large-scale solar distillation project was first constructed in 1872 in the Chilean mining town of Las Salinas. 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. 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 Solar water disinfection in Indonesia stills are the most economical for decentralized domestic purposes, while active multiple effect units are more suitable for large-scale applications. Solar water disinfection (SODIS) involves exposing water-filled plastic polyethylene terephthalate (PET) bottles to sunlight for several hours. Exposure times vary depending on weather and climate from a minimum of six hours to two days during fully overcast conditions. It is recommended by the World Health Organization as a viable method for household water treatment and safe storage. Over two million people in developing countries use this method for their daily drinking water. Small scale solar powered sewerage treatment plant. Solar energy may be used in a water stabilisation 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. Cooking Solar cookers use sunlight for cooking, drying and pasteurization. They can be grouped into three broad categories: box cookers, panel cookers and reflector cookers. The simplest solar cooker is the box cooker first built by Horace de Saussure in 1767. 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. Panel cookers use a reflective panel to direct sunlight onto an insulated container and reach temperatures The Solar Bowl in Auroville, India, concentrates comparable to box cookers. Reflector cookers use various sunlight on a movable receiver to produce steam concentrating geometries (dish, trough, Fresnel mirrors) to focus light for cooking. on a cooking container. These cookers reach temperatures of 315 °C and above but require direct light to function properly and must be repositioned to track the Sun. The solar bowl is a concentrating technology employed by the Solar Kitchen in Auroville, Pondicherry, India, where a stationary spherical reflector focuses light along a line perpendicular to the spheres interior surface, and a
Solar energy 14 computer control system moves the receiver to intersect this line. Steam is produced in the receiver at temperatures reaching 150 °C and then used for process heat in the kitchen. A reflector developed by Wolfgang Scheffler in 1986 is used in many solar kitchens. Scheffler reflectors are flexible parabolic dishes that combine aspects of trough and power tower concentrators. Polar tracking is used to follow the Suns daily course and the curvature of the reflector is adjusted for seasonal variations in the incident angle of sunlight. These reflectors can reach temperatures of 450–650 °C and have a fixed focal point, which simplifies cooking. The worlds largest Scheffler reflector system in Abu Road, Rajasthan, India is capable of cooking up to 35,000 meals a day. As of 2008, over 2,000 large Scheffler cookers had been built worldwide. 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, 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. Evaporation ponds are shallow pools that concentrate dissolved solids through evaporation. The use of evaporation ponds to obtain salt from sea water 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. 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. 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 and deliver outlet temperatures of 45–60 °C. The short payback period of transpired collectors (3 to 12 years) makes them a more cost-effective alternative than glazed collection systems. As of 2003, over 80 systems with a combined collector area of 35,000 m2 had been installed worldwide, including an 860 m2 collector in Costa Rica used for drying coffee beans and a 1,300 m2 collector in Coimbatore, India used for drying marigolds. 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. Commercial CSP plants were first developed in the 1980s, and the 354 MW SEGS CSP installation is the largest solar power plant in the world and is located in the Mojave Desert of California. Other large The PS10 concentrates sunlight from a field of CSP plants include the Solnova Solar Power Station (150 MW) and the heliostats on a central tower. Andasol solar power station (100 MW), both in Spain. The 214 MW Charanka Solar Park in India, is the world’s largest photovoltaic plant.
Solar energy 15 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. Photovoltaics A solar cell, or photovoltaic cell (PV), is a device that converts light into electric current using the photoelectric effect. The first solar cell was constructed by Charles Fritts in the 1880s. In 1931 a German engineer, Dr Bruno Lange, developed a photo cell using silver selenide in place of copper oxide. 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. Following the work of Russell Ohl in the 1940s, researchers Gerald Pearson, Calvin Fuller and Daryl Chapin 80 MW Okhotnykovo Solar Park in Ukraine. created the silicon solar cell in 1954. These early solar cells cost 286 USD/watt and reached efficiencies of 4.5–6%. 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. A variety of fuels can be produced by artificial photosynthesis. The multielectron catalytic NREL compilation of best research solar cell chemistry involved in making carbon-based fuels (such as methanol) efficiencies from 1976 to 2010 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. 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. Hydrogen production technologies 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 (2300-2600 °C). 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. 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 uses a 1 MW solar furnace to decompose zinc oxide (ZnO) at temperatures above 1200 °C. This initial reaction produces pure zinc, which can subsequently be reacted with water to produce hydrogen. Sandias Sunshine to Petrol (S2P) technology uses the high temperatures generated by concentrating sunlight along with a zirconia/ferrite catalyst to break down atmospheric carbon dioxide into oxygen and carbon monoxide (CO).
Solar energy 16 The carbon monoxide can then be used to synthesize conventional fuels such as methanol, gasoline and jet fuel. A photogalvanic device is a type of battery in which the cell solution (or equivalent) forms energy-rich chemical intermediates when illuminated. These energy-rich intermediates can potentially be stored and subsequently reacted at the electrodes to produce an electric potential. The ferric-thionine chemical cell is an example of this technology. Photoelectrochemical cells or PECs consist of a semiconductor, typically titanium dioxide or related titanates, immersed in an electrolyte. When the semiconductor is illuminated an electrical potential develops. There are two types of photoelectrochemical cells: photoelectric cells that convert light into electricity and photochemical cells that use light to drive chemical reactions such as electrolysis. A combination thermal/photochemical cell has also been proposed. The Stanford PETE process uses solar thermal energy to raise the temperature of a thermionic metal to about 800C to increase the rate of production of electricity to electrolyse atmospheric CO2 down to carbon or carbon monoxide which can then be used for fuel production, and the waste heat can be used as well. Solar vehicles 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 3021 kilometres (unknown operator: ustrong mi) across central Australia from Darwin to Adelaide. In 1987, when it was founded, the winners average speed was 67 kilometres per hour (unknown operator: ustrong mph) and by 2007 the winners average speed had improved to 90.87 kilometres per hour (unknown operator: ustrong mph). The North American Solar Challenge and the planned South African Solar Challenge are comparable competitions that reflect an international interest in the engineering and Australia hosts the World Solar Challenge where development of solar powered vehicles. solar cars like the Nuna3 race through a 3021 km (unknown operator: ustrong mi) course from Some vehicles use solar panels for auxiliary power, such as for air Darwin to Adelaide. conditioning, to keep the interior cool, thus reducing fuel consumption. In 1975, the first practical solar boat was constructed in England. By 1995, passenger boats incorporating PV panels began appearing and are now used extensively. 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. There are plans to circumnavigate the globe in 2010. 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 (unknown operator: ustrong 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 Helios UAV in solar powered flight. solar power. Developments then turned back to unmanned aerial
Solar energy 17 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 29524 metres (unknown operator: ustrong ft) in 2001. 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. 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. Solar sails are a proposed form of spacecraft propulsion using large membrane mirrors to exploit radiation pressure from the Sun. Unlike rockets, solar sails require no fuel. Although the thrust is small compared to rockets, it continues as long as the Sun shines onto the deployed sail and in the vacuum of space significant speeds can eventually be achieved. The High-altitude airship (HAA) is an unmanned, long-duration, lighter-than-air vehicle using helium gas for lift, and thin film solar cells for power. The United States Department of Defense Missile Defense Agency has contracted Lockheed Martin to construct it to enhance the Ballistic Missile Defense System (BMDS). Airships have some advantages for solar-powered flight: they do not require power to remain aloft, and an airships envelope presents a large area to the Sun. Energy storage methods Solar energy is not available at night, and energy storage is an important issue because modern energy systems usually assume continuous availability of energy. Thermal mass systems can store solar energy in the form of heat at domestically useful temperatures for daily or seasonal durations. Thermal storage systems generally use readily available materials with Solar Twos thermal storage system generated high specific heat capacities such as water, earth and stone. electricity during cloudy weather and at night. Well-designed systems can lower peak demand, shift time-of-use to off-peak hours and reduce overall heating and cooling requirements. Phase change materials such as paraffin wax and Glaubers salt are another thermal storage media. These materials are inexpensive, readily available, and can deliver domestically useful temperatures (approximately 64 °C). The "Dover House" (in Dover, Massachusetts) was the first to use a Glaubers salt heating system, in 1948. Solar energy can 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 used this method of energy storage, allowing it to store 1.44 TJ in its 68 m3 storage tank with an annual storage efficiency of about 99%. 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 often legally 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 is required to pay for the extra at the same rate as they charge consumers. Other legal 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. 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 to
Solar energy 18 run through a hydroelectric power generator. Development, deployment and economics 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. 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. Deployment strategies focused on incentive programs such as the Federal Photovoltaic Utilization Program in the US and the Sunshine Program in Japan. Other efforts included the formation of research facilities in the US (SERI, now NREL), Japan (NEDO), and Germany (Fraunhofer Institute for Solar Energy Systems ISE). Commercial solar water heaters began appearing in the United States in the 1890s. These systems saw increasing use until the 1920s but were gradually replaced by cheaper and more reliable heating fuels. 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 growth rates have averaged 20% per year since 1999. 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. 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: 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. In 2011, the International Energy Agency said that solar energy technologies such as photovoltaic panels, solar water heaters and power stations built with mirrors 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".
Solar energy 19 ISO Standards The International Organization for Standardization has established a number of 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. Notes  "Solar Energy Perspectives: Executive Summary" (http:/ / www. webcitation. org/ 63fIHKr1S) (PDF). International Energy Agency. 2011. Archived from the original (http:/ / www. iea. org/ Textbase/ npsum/ solar2011SUM. pdf) on 2011-12-03. .  Smil (1991), p. 240  "Natural Forcing of the Climate System" (http:/ / www. grida. no/ climate/ ipcc_tar/ wg1/ 041. htm#121). Intergovernmental Panel on Climate Change. . Retrieved 2007-09-29.  "Radiation Budget" (http:/ / marine. rutgers. edu/ mrs/ education/ class/ yuri/ erb. html). NASA Langley Research Center. 2006-10-17. . Retrieved 2007-09-29.  Somerville, Richard. "Historical Overview of Climate Change Science" (http:/ / www. ipcc. ch/ pdf/ assessment-report/ ar4/ wg1/ ar4-wg1-chapter1. pdf) (PDF). Intergovernmental Panel on Climate Change. . Retrieved 2007-09-29.  Vermass, Wim. "An Introduction to Photosynthesis and Its Applications" (http:/ / photoscience. la. asu. edu/ photosyn/ education/ photointro. html). Arizona State University. . Retrieved 2007-09-29.  Smil (2006), p. 12  Archer, Cristina; Jacobson, Mark. "Evaluation of Global Wind Power" (http:/ / www. stanford. edu/ group/ efmh/ winds/ global_winds. html). Stanford. . Retrieved 2008-06-03.  "Energy conversion by photosynthetic organisms" (http:/ / www. fao. org/ docrep/ w7241e/ w7241e06. htm#TopOfPage). Food and Agriculture Organization of the United Nations. . Retrieved 2008-05-25.  "World Consumption of Primary Energy by Energy Type and Selected Country Groups, 1980-2004" (http:/ / www. eia. doe. gov/ pub/ international/ iealf/ table18. xls). Energy Information Administration. . Retrieved 2008-05-17.  "World Total Net Electricity Consumption, 1980-2005" (http:/ / www. eia. doe. gov/ iea/ elec. html). Energy Information Administration. . Retrieved 2008-05-25.  Solar energy: A new day dawning? (http:/ / www. nature. com/ nature/ journal/ v443/ n7107/ full/ 443019a. html) retrieved 7 August 2008  Powering the Planet: Chemical challenges in solar energy utilization (http:/ / web. mit. edu/ mitpep/ pdf/ DGN_Powering_Planet. pdf) retrieved 7 August 2008  Exergy (available energy) Flow Charts (http:/ / gcep. stanford. edu/ research/ exergycharts. html) 2.7 YJ solar energy each year for two billion years vs. 1.4 YJ non-renewable resources available once.  http:/ / www. solarenergybyzip. com  Philibert, Cédric (2005). "The Present and Future use of Solar Thermal Energy as a Primary Source of Energy" (http:/ / www. webcitation. org/ 63rZo6Rn2). IEA. Archived from the original (http:/ / philibert. cedric. free. fr/ Downloads/ solarthermal. pdf) on 2011-12-12. .  "Darmstadt University of Technology solar decathlon home design" (http:/ / web. archive. org/ web/ 20071018035727/ http:/ / www. solardecathlon. de/ index. php/ our-house/ the-design). Darmstadt University of Technology. Archived from the original (http:/ / www. solardecathlon. de/ index. php/ our-house/ the-design) on October 18, 2007. . Retrieved 2008-04-25.  Schittich (2003), p. 14  Butti and Perlin (1981), p. 4, 159  Balcomb(1992)  Rosenfeld, Arthur; Romm, Joseph; Akbari, Hashem; Lloyd, Alan. "Painting the Town White -- and Green" (http:/ / web. archive. org/ web/ 20070714173907/ http:/ / eetd. lbl. gov/ HeatIsland/ PUBS/ PAINTING/ ). Heat Island Group. Archived from the original (http:/ / eetd. lbl. gov/ HeatIsland/ PUBS/ PAINTING/ ) on 2007-07-14. . Retrieved 2007-09-29.  Jeffrey C. Silvertooth. "Row Spacing, Plant Population, and Yield Relationships" (http:/ / ag. arizona. edu/ crop/ cotton/ comments/ april1999cc. html). University of Arizona. . Retrieved 2008-06-24.  Kaul (2005), p. 169–174  Butti and Perlin (1981), p. 42–46  Bénard (1981), p. 347  Leon (2006), p. 62  "A Powerhouse Winery" (http:/ / www. novusvinum. com/ news/ latest_news. html#gonzales). News Update. Novus Vinum. 2008-10-27. . Retrieved 2008-11-05.  Butti and Perlin (1981), p. 19  Butti and Perlin (1981), p. 41  "Prescription Act (1872 Chapter 71 2 and 3 Will 4)" (http:/ / www. opsi. gov. uk/ RevisedStatutes/ Acts/ ukpga/ 1832/ cukpga_18320071_en_1). Office of the Public Sector Information. . Retrieved 2008-05-18.
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Solar energy 24 External links • "How do Photovoltaics Work?" (http://science.nasa.gov/headlines/y2002/solarcells.htm). NASA. • Solar Energy Back in the Day (http://www.life.com/image/first/in-gallery/43861/ solar-energy-back-in-the-day) - slideshow by Life magazine • Compendium of Solar Cooker Designs (http://solarcooking.wikia.com/wiki/ Compendium_of_solar_cooker_designs) • U.S. Solar Farm Map (1 MW or Higher) (http://www.solarpowerworldonline.com/u-s-solar-farm-map/) Solar thermal energy Solar thermal energy (STE) is a technology for harnessing solar energy for thermal energy (heat). Solar thermal collectors are classified by the United States Energy Information Administration as low-, medium-, or high-temperature collectors. Low-temperature collectors are flat plates generally used to heat swimming pools. Medium-temperature collectors are also usually flat plates but are used for heating water or air for residential and commercial use. High-temperature collectors concentrate sunlight using mirrors or lenses and are generally used for electric power production. STE is different from and much more efficient than photovoltaics, which Solar thermal system for water heating in Santorini, Greece. converts solar energy directly into electricity. While existing generation facilities provide only 600 megawatts of solar thermal power worldwide in October 2009,  plants for an additional 400 megawatts are under construction and development is underway for concentrated solar power projects totalling 14,000 megawatts. Low-temperature collectors Of the 21000000 square feet (unknown operator: ustrong m2) of solar thermal collectors produced in the United States in 2007, 16000000 square feet (unknown operator: ustrong m2) were of the low-temperature variety. Low-temperature collectors are generally installed to heat swimming pools, although they can also be used for space heating. Collectors can use air or water as the medium to transfer the heat to their destination. Heating, cooling, and ventilation