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{{short description|Radiant light and heat from the Sun, harnessed with technology}}
{{about|radiant light and heat from the Sun that is harnessed using a range of technologies|more detail about the generation of electricity using solar energy|Solar power|the academic journal|Solar Energy (journal)}}
{{pp-semi|small=yes}}

{{Duplication|date=November 2022|dupe=Solar power}} <!--This article should talk about solar energy in general, not electricity-->
[[File:Sunset over the gulf of Mexico - iss042e034066.jpg|thumb|right|upright=1.5|The Sun produces [[electromagnetic radiation]] that can be harnessed as useful energy.]]
{{sustainable energy}}

'''Solar energy''' is [[solar irradiance|radiant]] [[sunlight|light]] and [[heat]] from the [[Sun]] that is harnessed using a range of technologies such as [[solar power]] to generate [[electricity]], [[solar thermal energy]] (including [[solar water heating]]), and [[solar architecture]].<ref name=ie11/><ref>{{cite web |url=http://www.rsc.org/ScienceAndTechnology/Policy/Documents/solar-fuels.asp |title=Energy |publisher=[[Royal Society of Chemistry]] |date=2 April 2014}}</ref> It is an essential 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 system]]s, [[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 [[Ventilation (architecture)|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 [[Climate change mitigation|mitigating global warming]] .... these advantages are global".<ref name=ie11>{{cite web|url=http://www.iea.org/Textbase/npsum/solar2011SUM.pdf |title=Solar Energy Perspectives: Executive Summary |year=2011 |publisher=International Energy Agency |archive-url=https://web.archive.org/web/20120113032718/http://www.iea.org/Textbase/npsum/solar2011SUM.pdf |archive-date=13 January 2012 |url-status=dead }}</ref>

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==Potential==
{{Further|Solar radiation}}
{{multiple image
|direction= vertical
|align    = right
|width    = 225
|image1   = Breakdown of the incoming solar energy.svg
|image2   = Solar land area.png
|caption1 = About half the incoming solar energy reaches the Earth's surface.
|caption2 = Average [[insolation]]. The theoretical area of the small black dots is sufficient to supply the [[World energy consumption|world's total energy needs]] of 18 [[Terawatt|TW]] with solar power.
}}
[[File:World GHI Solar-resource-map GlobalSolarAtlas World-Bank-Esmap-Solargis.png|thumb|upright=1.5|Global map of [[horizontal irradiation]]<ref>{{Cite web |url=https://globalsolaratlas.info/|title=Global Solar Atlas |access-date=14 June 2019|archive-date=27 November 2018|archive-url=https://web.archive.org/web/20181127131800/https://globalsolaratlas.info/|url-status=live}}</ref>]]
The Earth receives 174&nbsp;[[petawatt]]s (PW) of incoming solar radiation ([[insolation]]) at the upper [[Earth's atmosphere|atmosphere]].<ref>Smil (1991), p. 240</ref> Approximately 30% is reflected back to space while the rest, 122 PW, is absorbed by clouds, oceans and land masses. The [[electromagnetic spectrum|spectrum]] of solar light at the Earth's surface is mostly spread across the [[visible light|visible]] and [[near-infrared]] ranges with a small part in the [[near-ultraviolet]].<ref>{{cite web|title=Natural Forcing of the Climate System|publisher=Intergovernmental Panel on Climate Change|url=http://www.grida.no/climate/ipcc_tar/wg1/041.htm#121|access-date=29 September 2007|url-status=dead|archive-url=https://web.archive.org/web/20070929100134/http://www.grida.no/climate/ipcc_tar/wg1/041.htm#121|archive-date=29 September 2007}}</ref> Most of the world's population live in areas with insolation levels of 150–300 watts/m<sup>2</sup>, or 3.5–7.0 [[kilowatt-hour|kWh]]/m<sup>2</sup> per day.<ref>{{Cite book|last1=Karuppu|first1=Karthik|title=Solar Assessment Guidance: A Guide for Solar Trainee, Trainer & Assessor Examination|last2=Sitaraman|first2=Venk|last3=NVICO|publisher=Notion Press|year=2019|isbn=978-1646505227|language=en}}</ref>

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, [[cyclone]]s and [[anticyclone]]s.<ref>{{cite web|title=Radiation Budget|date=17 October 2006|publisher=NASA Langley Research Center|url=http://marine.rutgers.edu/mrs/education/class/yuri/erb.html|access-date=29 September 2007}}</ref> Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14&nbsp;°C.<ref>{{cite web|author=Somerville, Richard|title=Historical Overview of Climate Change Science|url=http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter1.pdf|publisher=Intergovernmental Panel on Climate Change|access-date=29 September 2007}}</ref> By [[photosynthesis]], green plants convert solar energy into chemically stored energy, which produces food, wood and the [[biomass]] from which [[fossil fuels]] are derived.<ref>{{cite web|author=Vermass, Wim|title=An Introduction to Photosynthesis and Its Applications|publisher=Arizona State University|url=http://photoscience.la.asu.edu/photosyn/education/photointro.html|access-date=29 September 2007|url-status=dead|archive-url=https://web.archive.org/web/19981203020943/http://photoscience.la.asu.edu/photosyn/education/photointro.html|archive-date=3 December 1998}}</ref>

The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 122 PW·year = 3,850,000&nbsp;[[Joule#Multiples|exajoules]] (EJ) per year.<ref name="Smil 2006, p. 12"/><!--Absorbed solar flux of 122 PW yields 3,850,000 EJ/year. --> In 2002 (2019), this was more energy in one hour (one hour and 25 minutes) than the world used in one year.<!--416 Quads vs. 410.7--><ref>{{cite journal|title=Solar energy: A new day dawning?: Silicon Valley sunrise|first=Oliver|last=Morton|date=6 September 2006|journal=Nature|volume=443|issue=7107|pages=19–22|doi=10.1038/443019a|pmid = 16957705|bibcode=2006Natur.443...19M|s2cid=13266273|doi-access=free}}</ref><ref>{{cite journal|url=http://web.mit.edu/mitpep/pdf/DGN_Powering_Planet.pdf|title=Powering the Planet: Chemical challenges in solar energy utilization|journal=Proceedings of the National Academy of Sciences|volume=103|issue=43|pages=15729–35|access-date=7 August 2008|bibcode=2006PNAS..10315729L|last1=Lewis|first1=N. S.|last2=Nocera|first2=D. G.|year=2006|doi=10.1073/pnas.0603395103|pmid=17043226|pmc=1635072|doi-access=free}}</ref> Photosynthesis captures approximately 3,000&nbsp;EJ per year in biomass.<ref>{{cite web|publisher=Food and Agriculture Organization of the United Nations|url=http://www.fao.org/docrep/w7241e/w7241e06.htm#TopOfPage|title=Energy conversion by photosynthetic organisms|access-date=25 May 2008}}</ref>

{| class="wikitable" style="margin-right: 12px;"
|+Yearly solar fluxes & human consumption<sup>1</sup>
|Solar
| align=right | 3,850,000
| align=center |<ref name="Smil 2006, p. 12">Smil (2006), p. 12</ref><!-- Smil quotes an absorbed solar flux of 122 PW => 3,850 ZJ. -->
|-
|Wind
| align=right | 2,250
| align=center |<ref>{{cite web|author=Archer, Cristina|author2=Jacobson, Mark|title=Evaluation of Global Wind Power|publisher=Stanford|url=http://www.stanford.edu/group/efmh/winds/global_winds.html|access-date=3 June 2008}}</ref>
|-
|Biomass potential
| align=right |~200
| align=center |<ref>{{cite web|publisher=Renewable and Appropriate Energy Laboratory|url=http://www-fa.upc.es/personals/fluids/oriol/ale/eolss.pdf|title=Renewable Energy Sources|page=12|access-date=6 December 2012|url-status=dead|archive-url=https://web.archive.org/web/20121119020636/http://www-fa.upc.es/personals/fluids/oriol/ale/eolss.pdf|archive-date=19 November 2012}}</ref>
|-
|[[World energy consumption|Primary energy use]]<sup>2</sup>
| align=right |633
| align=center |<ref>{{cite web|publisher=[[Energy Information Administration]]|url=http://www.eia.gov/cfapps/ipdbproject/IEDIndex3.cfm?tid=44&pid=44&aid=2|title=Total Primary Energy Consumption|access-date=28 June 2022}}</ref><!-- converted from 600.266 quadrillion BTUs -->
|-
|Electricity<sup>2</sup>
| align=right |~86
| align=center |<ref>{{cite web|publisher=Energy Information Administration|url=http://www.eia.gov/cfapps/ipdbproject/IEDIndex3.cfm?tid=2&pid=2&aid=2|title=Total Electricity Net Consumption|access-date=28 June 2022}}</ref><!-- converted from 23,787 TWh -->
|-
! colspan=3 style="font-size: 80%; font-weight: normal; text-align: left; padding: 6px 2px 4px 4px;"| <sup>1</sup> Energy given in [[Orders of magnitude (energy)|Exajoule]] (EJ) = 10<sup>18</sup> [[Joule|J]] = 278 [[terawatt-hour|TWh]]&nbsp;<br /><sup>2</sup> Consumption as of year 2019
|}

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. In 2021, [[Carbon Tracker Initiative]] estimated the land area needed to generate all our energy from solar alone was 450,000 [[Square kilometre|km<sup>2</sup>]] — or about the same as the area of [[Sweden]], or the area of [[Morocco]], or the area of [[California]] (0.3% of the Earth's total land area).<ref>{{Cite web|last=Bond|first=Kingsmill|date=April 2021|title=The sky's the limit|url=https://epbr.com.br/wp-content/uploads/2021/04/Sky-the-limit-report_Apr21-compressed.pdf|url-status=live|archive-url=https://web.archive.org/web/20210430191920/https://epbr.com.br/wp-content/uploads/2021/04/Sky-the-limit-report_Apr21-compressed.pdf|archive-date=April 30, 2021|access-date=October 22, 2021|website=epbr|publisher=Carbon Tracker Initiative|page=6}}</ref>

Solar technologies are categorized 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 the distance from the Equator. Although solar energy refers primarily to the use of solar radiation for practical ends, all types of renewable energy, other than [[geothermal power]] and [[tidal power]], are derived either directly or indirectly from the Sun.

Active solar techniques use photovoltaics, [[concentrated solar power]], [[solar thermal collector]]s, pumps, and fans to convert sunlight into useful output. Passive solar techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air, and referencing{{clarify|date=December 2023}} 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 alternative resources and are generally considered demand-side technologies.<ref name="IEA Solar Thermal"/>

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. This took into account factors such as insolation, cloud cover, and the land that is usable by humans. It was stated that solar energy has a global potential of {{convert|1600|to|49800|EJ|kWh|sigfig=2}} per year ''(see table below)''.<ref name="World Energy Assessment">{{cite web |date=September 2000 |title=Energy and the challenge of sustainability |url=http://www.undp.org/content/dam/aplaws/publication/en/publications/environment-energy/www-ee-library/sustainable-energy/world-energy-assessment-energy-and-the-challenge-of-sustainability/World%20Energy%20Assessment-2000.pdf |access-date=17 January 2017 |work=United Nations Development Programme and [[World Energy Council]]}}</ref>

{| class="wikitable" style="text-align: center;"
|+Annual solar energy potential by region (Exajoules) <ref name="World Energy Assessment" />
! Region !! North America !! Latin America<br>and Caribbean !! Western<br>Europe !! Central and<br>Eastern Europe !! Former<br>Soviet Union !! Middle East and<br>North Africa !! Sub-Saharan<br>Africa !! Pacific<br>Asia !! South<br>Asia !! Centrally<br>planned<br>Asia !! Pacific<br>OECD
|-
| align=left | Minimum || 181.1 || 112.6 || 25.1 || 4.5 || 199.3 || 412.4 || 371.9 || 41.0 || 38.8 || 115.5 || 72.6
|-
| align=left | Maximum || 7,410 || 3,385 || 914 || 154 || 8,655 || 11,060 || 9,528 || 994 || 1,339 || 4,135 || 2,263
|-
! colspan=12 style="font-weight: normal; text-align: left; padding: 6px 4px; font-size: 92%;" |''Notes:''
* 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)<ref name="World Energy Assessment" />
|}

== Thermal energy ==
{{Main|Solar thermal energy}}
Solar thermal technologies can be used for water heating, space heating, space cooling and process heat generation.<ref>{{cite web|title=Solar Energy Technologies and Applications|publisher=Canadian Renewable Energy Network|url=http://www.canren.gc.ca/tech_appl/index.asp?CaId=5&PgId=121|access-date=22 October 2007|url-status=dead|archive-url=https://web.archive.org/web/20020625234404/http://www.canren.gc.ca/tech_appl/index.asp?CaId=5&PgId=121|archive-date=25 June 2002}}</ref>

===Early commercial adaptation===
In 1878, at the Universal Exposition in Paris, [[Augustin Mouchot]] successfully demonstrated a solar steam engine but could not continue development because of cheap coal and other factors.
[[File: US Patent 1240890.pdf|thumb|upright=0.80|1917 patent drawing of Shuman's solar collector]]
In 1897, [[Frank Shuman]], a US 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 [[C. V. Boys|Charles Vernon Boys]],<ref name="Kryza2003">{{cite book | author = Frank Kryza | date = 2003 | title = The Power of Light | publisher = McGraw Hill Professional | pages = 64,135 | isbn = 978-0-07-140021-3 | url = https://books.google.com/books?id=OEhHtP24ybIC|access-date=30 August 2022}}</ref> 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 energy|solar thermal power station]] in [[Maadi]], [[Egypt]], between 1912 and 1913. His plant used [[parabolic trough]]s to power a {{convert|45|–|52|kW|hp|lk=out}} engine that pumped more than {{convert|22000|litres}} of water per minute from the [[Nile River]] to adjacent cotton fields. Although the outbreak of World War I and the discovery of [[Petroleum industry|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.<ref>{{cite book|last=Smith|first=Zachary Alden|author2=Taylor, Katrina D.|title=Renewable And Alternative Energy Resources: A Reference Handbook|url=https://archive.org/details/unset0000unse_z1v3|url-access=registration|publisher=[[ABC-CLIO]]|date=2008|page=[https://archive.org/details/unset0000unse_z1v3/page/174 174]|isbn=978-1-59884-089-6}}</ref> In 1916 Shuman was quoted in the media advocating solar energy's utilization, saying:
{{quote|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<ref name="nytimes.com">{{cite web|url=https://timesmachine.nytimes.com/timesmachine/1916/07/02/104680095.pdf|title=American Inventor Uses Egypt's Sun for Power – Appliance Concentrates the Heat Rays and Produces Steam, Which Can Be Used to Drive Irrigation Pumps in Hot Climates |date=2 July 1916|work=[[The New York Times]]}}</ref>}}

===Water heating===
{{Main|Solar hot water|Solar combisystem}}
[[File:Twice Cropped Zonnecollectoren.JPG|thumb|upright|Solar water heaters facing the [[Sun]] to maximize gain]]
Solar hot water systems use sunlight to heat water. In middle geographical latitudes (between 40&nbsp;degrees north and 40&nbsp;degrees south), 60 to 70% of the domestic hot water use, with water temperatures up to {{convert|60|C|F}}, can be provided by solar heating systems.<ref>{{cite web|title=Renewables for Heating and Cooling|publisher=International Energy Agency|url=http://www.iea.org/textbase/npsum/Renewables_Heating_Cooling07SUM.pdf|access-date=13 August 2015|archive-date=24 September 2015|archive-url=https://web.archive.org/web/20150924045820/http://www.iea.org/textbase/npsum/Renewables_Heating_Cooling07SUM.pdf|url-status=dead}}</ref> 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.<ref>{{cite web|title=Solar Heat Worldwide (Markets and Contributions to the Energy Supply 2005)|publisher=International Energy Agency|author=Weiss, Werner|author2=Bergmann, Irene|author3=Faninger, Gerhard|url=http://www.iea-shc.org/data/sites/1/publications/Solar_Heat_Worldwide-2007.pdf|access-date=30 May 2008}}</ref>

As of 2015, the total installed capacity of solar hot water systems was approximately 436 [[GWth|thermal]] [[gigawatt]] (GW<sub>th</sub>), and China is the world leader in their deployment with 309&nbsp;GW<sub>th</sub> installed, taken up 71% of the market.<ref name = "ADB-China2019">{{Cite journal|title=Solar District Heating In The People's Republic of China
|url=https://www.adb.org/sites/default/files/publication/514916/solar-district-heating-peoples-republic-china.pdf|journal=Status and Development Potential|publisher=[[Asian Development Bank]]|publication-date=1 July 2019|pages=23|access-date=6 July 2021}}</ref> [[Israel]] and [[Cyprus]] are the per capita leaders in the use of solar hot water systems with over 90% of homes using them.<ref>{{cite web|author=Del Chiaro, Bernadette|author2=Telleen-Lawton, Timothy|title=Solar Water Heating (How California Can Reduce Its Dependence on Natural Gas)|publisher=Environment California Research and Policy Center|url=http://www.environmentcalifornia.org/uploads/at/56/at563bKwmfrtJI6fKl9U_w/Solar-Water-Heating.pdf|access-date=29 September 2007|url-status=dead|archive-url=https://web.archive.org/web/20070927082332/http://www.environmentcalifornia.org/uploads/at/56/at563bKwmfrtJI6fKl9U_w/Solar-Water-Heating.pdf|archive-date=27 September 2007}}</ref> In the United States, Canada, and Australia, heating swimming pools is the dominant application of solar hot water with an installed capacity of 18&nbsp;GW<sub>th</sub> as of 2005.<ref name="IEA Solar Thermal">{{cite web|url=http://philibert.cedric.free.fr/Downloads/solarthermal.pdf |title=The Present and Future use of Solar Thermal Energy as a Primary Source of Energy |last=Philibert |first=Cédric |year=2005 |publisher=IEA |archive-url=https://web.archive.org/web/20120426044500/http://philibert.cedric.free.fr/Downloads/solarthermal.pdf |archive-date=26 April 2012 |url-status=live }}</ref>

===Heating, cooling and ventilation===
{{Main|Solar heating|Thermal mass|Solar chimney|Solar air conditioning}}
In the United States, [[HVAC|heating, ventilation and air conditioning]] (HVAC) systems account for 30% (4.65&nbsp;EJ/yr)<!--converted from 30% of 14.7 quads: 1.055 EJ/quad x 14.7 quad x 30%--> of the energy used in commercial buildings and nearly 50% (10.1&nbsp;EJ/yr)<!--source quotes residential HVAC energy usage of 10.1 EJ and total energy use of 20.3 EJ--> of the energy used in residential buildings.<ref>{{cite web|author=Apte, J.|display-authors=etal|title=Future Advanced Windows for Zero-Energy Homes|publisher=American Society of Heating, Refrigerating and Air-Conditioning Engineers|url=http://windows.lbl.gov/adv_Sys/ASHRAE%20Final%20Dynamic%20Windows.pdf|access-date=9 April 2008|url-status=dead|archive-url=https://web.archive.org/web/20080410212544/http://windows.lbl.gov/adv_Sys/ASHRAE%20Final%20Dynamic%20Windows.pdf|archive-date=10 April 2008}}</ref><ref>{{cite web|title=Energy Consumption Characteristics of Commercial Building HVAC Systems Volume III: Energy Savings Potential|publisher=United States Department of Energy|url=http://www.doas-radiant.psu.edu/DOE_report.pdf|access-date=24 June 2008}}</ref> Solar heating, cooling and ventilation technologies can be used to offset a portion of this energy.  Use of solar for heating can roughly be divided into [[Passive solar building design|passive solar]] concepts and [[Solar thermal energy|active solar]] concepts, depending on whether active elements such as [[solar tracker|sun tracking]] and solar concentrator optics are used.

[[File:Flipped MIT Solar One house.png|thumb|left|[[Massachusetts Institute of Technology|MIT]]'s Solar House #1, built in 1939 in the US, 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 duly incorporated, thermal mass maintains space temperatures in a comfortable range and reduces the need for auxiliary heating and cooling equipment.<ref>Mazria (1979), pp. 29–35</ref>

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<ref>{{cite news|last=Bright|first=David|date=18 February 1977|title=Passive solar heating simpler for the average owner|url=https://news.google.com/newspapers?id=beAzAAAAIBAJ&pg=1418,1115815&dq=improved+by+using+glazing+and+thermal+mass&hl=en|newspaper=Bangor Daily News|access-date=3 July 2011}}</ref> 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.<ref>Mazria (1979), p. 255</ref> 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.<ref>Balcomb (1992), p. 56</ref> 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]].<ref>Balcomb (1992), p. 57</ref>

===Cooking===
{{Main|Solar cooker}}
[[File:Auroville Solar Bowl.JPG|thumb|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.<ref>Anderson and Palkovic (1994), p. xi</ref> The simplest solar cooker is the box cooker first built by [[Horace de Saussure]] in 1767.<ref>Butti and Perlin (1981), pp. 54–59</ref> 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 {{convert|90-150|C}}.<ref>, Anderson and Palkovic (1994), p. xii</ref> 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 {{convert|315|C}} and above but require direct light to function properly and must be repositioned to track the Sun.<ref>Anderson and Palkovic (1994), p. xiii</ref>

===Process heat===
{{Main|Solar pond|Salt evaporation pond|Solar furnace}}
Solar concentrating technologies such as parabolic dish, trough and Scheffler reflectors can provide process heat for commercial and industrial applications. The first commercial system was the [[Solar Total Energy Project]] (STEP) in Shenandoah, Georgia, 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&nbsp;kW of electricity plus thermal energy in the form of 401&nbsp;kW steam and 468&nbsp;kW chilled water and had a one-hour peak load thermal storage.<ref>{{cite journal|title=Shenandoah Solar Total Energy Project|journal=NASA Sti/Recon Technical Report N |volume=83 |pages=25168 |author1=Stine, W.B.  |author2=Harrigan, R.W. |name-list-style=amp |publisher=John Wiley|url=http://www.powerfromthesun.net/Book/chapter16/chapter16.html|access-date=20 July 2008|bibcode=1982STIN...8325168L |year=1982 }}</ref> 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.<ref>Bartlett (1998), pp. 393–94</ref> 

[[Clothes line]]s, [[clotheshorse]]s, 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.<ref>{{cite web|title=Right to Dry Legislation in New England and Other States|publisher=Connecticut General Assembly|author=Thomson-Philbrook, Julia|url=http://www.cga.ct.gov/2008/rpt/2008-R-0042.htm|access-date=27 May 2008}}</ref> Unglazed transpired collectors (UTC) are perforated sun-facing walls used for preheating ventilation air. UTCs can raise the incoming air temperature up to {{convert|22|C-change}} and deliver outlet temperatures of {{convert|45|-|60|C}}.<ref name="UTC">{{cite web|title=Solar Buildings (Transpired Air Collectors – Ventilation Preheating)|publisher=National Renewable Energy Laboratory|url=http://www.nrel.gov/docs/fy06osti/29913.pdf|access-date=29 September 2007}}</ref> The short payback period of transpired collectors (3 to 12&nbsp;years) makes them a more cost-effective alternative than glazed collection systems.<ref name="UTC"/> As of 2003, over 80 systems with a combined collector area of {{convert|35000|m2}} had been installed worldwide, including an {{convert|860|m2|abbr=on}} collector in [[Costa Rica]] used for drying coffee beans and a {{convert|1300|m2|abbr=on}} collector in [[Coimbatore]], India, used for drying marigolds.<ref name="Leon 2006"/>{{needs update|date=October 2021}}

===Water treatment===
{{Main|Solar still|Solar water disinfection|Solar desalination|Solar Powered Desalination Unit}}
[[File:Indonesia-sodis-gross.jpg|thumb|[[Solar water disinfection]] in Indonesia]]
Solar distillation can be used to make [[saline water|saline]] or [[brackish water]] potable. The first recorded instance of this was by 16th-century Arab alchemists.<ref name="Tiwari 2003">Tiwari (2003), pp. 368–71</ref> A large-scale solar distillation project was first constructed in 1872 in the [[Chile]]an mining town of Las Salinas.<ref name="Daniels 1964">Daniels (1964), p. 6</ref> The plant, which had solar collection area of {{convert|4700|m2|abbr=on}}, could produce up to {{convert|22700|L|abbr=on}} per day and operate for 40&nbsp;years.<ref name="Daniels 1964"/> 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.<ref name="Tiwari 2003"/>

Solar water [[disinfection]] (SODIS) involves exposing water-filled plastic [[polyethylene terephthalate]] (PET) bottles to sunlight for several hours.<ref>{{cite web|title=SODIS solar water disinfection|publisher=EAWAG (The Swiss Federal Institute for Environmental Science and Technology)|url=http://www.sodis.ch/index_EN|access-date=2 May 2008}}</ref> Exposure times vary depending on weather and climate from a minimum of six hours to two days during fully overcast conditions.<ref name="SODIS CDC">{{cite web|title=Household Water Treatment Options in Developing Countries: Solar Disinfection (SODIS) |publisher=Centers for Disease Control and Prevention |url=http://www.ehproject.org/PDF/ehkm/cdc-options_sodis.pdf |access-date=13 May 2008 |archive-url=https://web.archive.org/web/20080529090729/http://www.ehproject.org/PDF/ehkm/cdc-options_sodis.pdf |archive-date=29 May 2008 |url-status=dead }}</ref> It is recommended by the [[World Health Organization]] as a viable method for household water treatment and safe storage.<ref>{{cite web|title=Household Water Treatment and Safe Storage|publisher=World Health Organization|url=https://www.who.int/household_water/en/|archive-url=https://web.archive.org/web/20041025024316/http://www.who.int/household_water/en/|url-status=dead|archive-date=October 25, 2004|access-date=2 May 2008}}</ref> Over two million people in developing countries use this method for their daily drinking water.<ref name="SODIS CDC"/>

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.<ref>{{cite journal|author1=Shilton A.N. |author2=Powell N. |author3=Mara D.D. |author4=Craggs R. |title=Solar-powered aeration and disinfection, anaerobic co-digestion, biological CO(2) scrubbing and biofuel production: the energy and carbon management opportunities of waste stabilization ponds|journal=Water Sci. Technol.|volume=58|issue=1|pages=253–58|year=2008|pmid=18653962|doi=10.2166/wst.2008.666|doi-access=}}</ref><ref>{{cite journal|author1=Tadesse I. |author2=Isoaho S.A. |author3=Green F.B. |author4=Puhakka J.A. |title=Removal of organics and nutrients from tannery effluent by advanced integrated Wastewater Pond Systems technology|journal=Water Sci. Technol.|volume=48|issue=2|pages=307–14|year=2003|pmid=14510225|doi=10.2166/wst.2003.0135 }}</ref>

===Molten salt technology===

Molten salt can be employed as a [[thermal energy storage]] method to retain thermal energy collected by a [[Solar power tower|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 to 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.<ref>{{cite web|url=http://www.sandia.gov/Renewable_Energy/solarthermal/NSTTF/salt.htm |title=Advantages of Using Molten Salt |access-date=14 July 2011 |last=Mancini |first=Tom |date=10 January 2006 |publisher=Sandia National Laboratories |archive-url=https://web.archive.org/web/20110605094349/http://www.sandia.gov/Renewable_Energy/solarthermal/NSTTF/salt.htm |archive-date=5 June 2011 |url-status=dead }}</ref><ref>[http://adsabs.harvard.edu/abs/1977htec.proc...39J Molten salt energy storage system – A feasibility study] Jones, B.G.; Roy, R.P.; Bohl, R.W. (1977) – Smithsonian/NASA ADS Physics Abstract Service. Abstract accessed December 2007</ref><ref>{{cite web|last=Biello|first=David|title=How to Use Solar Energy at Night|url=http://www.scientificamerican.com/article.cfm?id=how-to-use-solar-energy-at-night|work=Scientific American|access-date=19 June 2011}}</ref> The molten salt mixtures vary. The most extended mixture contains [[sodium nitrate]], [[potassium nitrate]] and [[calcium nitrate]]. It is non-flammable and non-toxic, and has already been used in the chemical and metals industries as a heat-transport fluid. Hence, experience with such systems exists in non-solar applications.

The salt melts at {{convert|131|°C|°F}}. It is kept liquid at {{convert|288|°C|°F}} in an insulated "cold" storage tank. The liquid salt is pumped through panels in a solar collector where the focused irradiance heats it to {{convert|566|°C|°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.<ref>[[Robert Ehrlich (physicist)|Ehrlich, Robert]], 2013, "Renewable Energy: A First Course," CRC Press, Chap. 13.1.22 ''Thermal storage'' p. 375 {{ISBN|978-1-4398-6115-8}}</ref>

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 {{convert|9.1|m|ft}} tall and {{convert|24|m|ft}} in diameter to drive it for four hours by this design.

Several [[parabolic trough]] power plants in Spain<ref>[http://www.nrel.gov/csp/troughnet/thermal_energy_storage.html Parabolic Trough Thermal Energy Storage Technology] {{webarchive|url=https://web.archive.org/web/20130901224906/http://www.nrel.gov/csp/troughnet/thermal_energy_storage.html |date=1 September 2013 }}  Parabolic Trough Solar Power Network. 4 April 2007. Accessed December 2007</ref> 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. In Chile, The Cerro Dominador power plant has a 110&nbsp;MW solar-thermal tower, the heat is transferred to [[Thermal energy storage#Molten salt technology|molten salts]].<ref>[https://archive.today/20140131162845/http://www.thisischile.cl/9090/2/chile-to-welcome-largest-solar-concentration-plant-in-lat-am/News.aspx Chile to welcome largest solar concentration plant in Lat Am] www.thisischile.cl Thursday, January 16, 2014 retrieved January 27, 2014</ref>
The molten salts then transfer their heat in a heat exchanger to water, generating superheated steam, which feeds a turbine that transforms the kinetic energy of the steam into electric energy using the [[Rankine cycle]].<ref>{{cite web|url= http://www.nrel.gov/csp/solarpaces/project_detail.cfm/projectID=3275 |title=Concentrating Solar Power Projects - Atacama-1 |publisher=[[National Renewable Energy Laboratory]] |date= 1 July 2015 |accessdate=10 September 2016}}</ref> In this way, the Cerro Dominador plant is capable of generating around 110 MW of power.<ref>[http://reneweconomy.com.au/2014/abengoa-to-build-110mw-solar-tower-storage-plant-in-chile-24839 Abengoa to build 110MW solar tower storage plant in Chile] reneweconomy.com.au/ By Giles Parkinson on 13 January 2014</ref>
The plant has an advanced storage system enabling it to generate electricity for up to 17.5 hours without direct solar radiation, which allows it to provide a stable electricity supply without interruptions if required. The Project secured up to 950 GW·h per year sale. Another project is the María Elena plant<ref>[http://www.thisischile.cl/8861/2/Chile-greenlights-enormous-400-megawatt-solar-project/News.aspx Here comes the sun Chile greenlights enormous 400-megawatt solar project] www.thisischile.cl Friday, 23 August 2013 retrieved 30 August 2013</ref>  is a 400&nbsp;MW thermo-solar complex in the northern [[Chile]]an region of [[Antofagasta Region|Antofagasta]] employing molten salt technology.

==Electricity production==
{{Excerpt|Solar power|only=paragraphs}}

==Concentrated solar power==
{{Main|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 solar tower collectors, the concentrating linear Fresnel reflector, and the Stirling dish. 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.<ref>Martin and Goswami (2005), p. 45</ref>  Designs need to account for the risk of a [[dust storm]], [[hail]], or another extreme weather event that can damage the fine glass surfaces of solar power plants.  Metal grills would allow a high percentage of sunlight to enter the mirrors and solar panels while also preventing most damage.

==Architecture and urban planning==
{{Main|Passive solar building design|Urban heat island}}
[[File:Technische Universität Darmstadt - Solar Decathlon 2007.jpg|thumb|[[Darmstadt University of Technology]], Germany, won the 2007 [[Solar Decathlon]] in Washington, DC with this [[passive house]] designed for humid and hot subtropical climate.<ref>{{cite web|title=Darmstadt University of Technology solar decathlon home design |publisher=Darmstadt University of Technology |url=http://www.solardecathlon.de/index.php/our-house/the-design |access-date=25 April 2008 |archive-url=https://web.archive.org/web/20071018035727/http://www.solardecathlon.de/index.php/our-house/the-design |archive-date=18 October 2007 |url-status=dead }}</ref>]]

Sunlight has influenced building design since the beginning of architectural history.<ref name= "Schittich 2003">Schittich (2003), p. 14</ref> Advanced solar architecture and urban planning methods were first employed by the [[ancient Greece|Greeks]] and [[Feng shui#Archaeology|Chinese]], who oriented their buildings toward the south to provide light and warmth.<ref>Butti and Perlin (1981), pp. 4, 159</ref>

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 (Building)|thermal mass]].<ref name= "Schittich 2003"/> 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.<ref name="Schittich 2003"/> The most recent approaches to solar design use computer modeling tying together [[Daylighting (architecture)|solar lighting]], [[solar heating|heating]] and [[solar air conditioning|ventilation]] systems in an integrated [[solar design]] package.<ref>Balcomb (1992)</ref> 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 [[albedo]]s and higher [[heat capacity|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&nbsp;°C at an estimated cost of US$1&nbsp; billion, giving estimated total annual benefits of US$530&nbsp; million from reduced air-conditioning costs and healthcare savings.<ref>{{cite web|author=Rosenfeld, Arthur |display-authors=etal |title=Painting the Town White – and Green |publisher=Heat Island Group |url=http://eetd.lbl.gov/HeatIsland/PUBS/PAINTING/ |access-date=29 September 2007 |archive-url=https://web.archive.org/web/20070714173907/http://eetd.lbl.gov/HeatIsland/PUBS/PAINTING/ |archive-date=14 July 2007 |url-status=dead }}</ref>

==Agriculture and horticulture==
[[File:Westland kassen.jpg|thumb|[[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 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.<ref>{{cite web|title=Row Spacing, Plant Population, and Yield Relationships|author=Jeffrey C. Silvertooth|publisher=University of Arizona|url=http://ag.arizona.edu/crop/cotton/comments/april1999cc.html|access-date=24 June 2008}}</ref><ref>Kaul (2005), pp. 169–74</ref> 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 [[Solar power in the United Kingdom|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 [[Solar tracker|tracking mechanism]] which could pivot to follow the Sun.<ref>Butti and Perlin (1981), pp. 42–46</ref> Applications of solar energy in agriculture aside from growing crops include pumping water, drying crops, brooding chicks and drying chicken manure.<ref name="Leon 2006">Leon (2006), p. 62</ref><ref>Bénard (1981), p. 347</ref> More recently the technology has been embraced by [[Winemakers|vintners]], who use the energy generated by solar panels to power grape presses.<ref>{{cite web|url=http://www.novusvinum.com/news/latest_news.html#gonzales|title=A Powerhouse Winery|access-date=5 November 2008|work=News Update|publisher=Novus Vinum|date=27 October 2008}}</ref>

[[Greenhouse]]s 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]].<ref>Butti and Perlin (1981), p. 19</ref> The first modern greenhouses were built in Europe in the 16th century to keep exotic plants brought back from explorations abroad.<ref>Butti and Perlin (1981), p. 41</ref> Greenhouses remain an important part of horticulture today. Plastic transparent materials have also been used to similar effect in [[polytunnel]]s and [[row cover]]s.

==Transport==
{{Main|Solar vehicle|Solar-charged vehicle|Electric boat|Solar balloon|Solar aircraft}}
{{multiple image
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|image1=Nuna 7.jpg
|image2=Flea Hop HB-SIA - Solar Impulse.jpg
|caption1=[[Nuna 7|Winner]] of the 2013 [[World Solar Challenge]] in Australia
|caption2=[[Solar aircraft|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 {{convert|3021|km|mi}} across central Australia from [[Darwin, Northern Territory|Darwin]] to [[Adelaide]]. In 1987, when it was founded, the winner's average speed was {{convert|67|km/h|mph}} and by 2007 the winner's average speed had improved to {{convert|90.87|km/h|mph|2}}.<ref>{{cite web|title=The World Solar Challenge – The Background |publisher=Australian and New Zealand Solar Energy Society |url=http://www.anzses.org/files/The%20WORLD%20Solar%20Challenge.pdf |access-date=5 August 2008 |archive-url=https://web.archive.org/web/20080719140545/http://www.anzses.org/files/The%20WORLD%20Solar%20Challenge.pdf |archive-date=19 July 2008 |url-status=dead }}</ref>
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.<ref>{{cite web|title=North American Solar Challenge|publisher=New Resources Group|url=http://americansolarchallenge.org/|access-date=3 July 2008}}</ref><ref>{{cite web|title=South African Solar Challenge |publisher=Advanced Energy Foundation |url=http://www.solarchallenge.org.za/Default.aspx?AspxAutoDetectCookieSupport=1 |access-date=3 July 2008 |archive-url=https://web.archive.org/web/20080612165911/http://www.solarchallenge.org.za/Default.aspx?AspxAutoDetectCookieSupport=1 |archive-date=12 June 2008 |url-status=dead }}</ref>

Some vehicles use solar panels for auxiliary power, such as for air conditioning, to keep the interior cool, thus reducing fuel consumption.<ref>{{cite book|url=https://ieeexplore.ieee.org/document/152037|title=Vehicle auxiliary power applications for solar cells|year=1991|pages=187–191|publisher=Institution of Electrical Engineers |access-date=11 October 2008|isbn=0-85296-525-7}}</ref><ref>{{cite web|url=http://www.systaic.com/press/press-release/systaic-ag-demand-for-car-solar-roofs-skyrockets.html |title=Systaic AG: Demand for Car Solar Roofs Skyrockets |access-date=29 March 2011 |url-status=dead |archive-url=https://web.archive.org/web/20090505004053/http://www.systaic.com/press/press-release/systaic-ag-demand-for-car-solar-roofs-skyrockets.html |archive-date=5 May 2009 }}</ref>

In 1975, the first practical solar boat was constructed in England.<ref>''Electrical Review'' Vol. 201, No. 7, 12 August 1977</ref> By 1995, passenger boats incorporating PV panels began appearing and are now used extensively.<ref>{{cite web|author=Schmidt, Theodor|title=Solar Ships for the new Millennium|publisher=TO Engineering|url=http://www.umwelteinsatz.ch/IBS/solship2.html|access-date=30 September 2007|url-status=dead|archive-url=https://web.archive.org/web/20071009022633/http://www.umwelteinsatz.ch/IBS/solship2.html|archive-date=9 October 2007}}</ref> 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.<ref>{{cite web|title=The sun21 completes the first transatlantic crossing with a solar powered boat|publisher=Transatlantic 21|url=http://www.transatlantic21.org/|access-date=30 September 2007}}</ref> There were plans to circumnavigate the globe in 2010.<ref>{{cite web|title=PlanetSolar, the first solar-powered round-the-world voyage|date=14 August 2015|publisher=PlanetSolar|url=http://ecoenergyproducts.info/solar-energy/first-solar-energy-powered-boat-circumnavigation/|access-date=20 November 2016}}</ref>

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 {{convert|40|ft|abbr=on}}. In 1980, the ''[[Gossamer Albatross#Solar-powered variants|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.<ref>{{cite web|url=http://www.evworld.com/article.cfm?storyid=709 |title=EVWORLD FEATURE: Sunseeker Seeks New Records:SUNSEEKER &#124; SAILPLANE &#124; SOARING &#124; GLIDER &#124; ELECTRIC &#124; RAYMOND &#124; PV &#124; PHOTOVOLTAIC &#124; SOLAR &#124; SUN &#124; PLANE &#124; AIRCRAFT &#124; KITTYHAWK &#124; AC PROPULSION |access-date=8 February 2008 |url-status=dead |archive-url=https://web.archive.org/web/20080208120356/http://www.evworld.com/article.cfm?storyid=709 |archive-date=8 February 2008 }}</ref> Developments then turned back to unmanned aerial vehicles (UAV) with the ''[[NASA Pathfinder|Pathfinder]]'' (1997) and subsequent designs, culminating in the ''[[Helios Prototype|Helios]]'' which set the altitude record for a non-rocket-propelled aircraft at {{convert|29524|m|ft}} in 2001.<ref>{{cite web|title=Solar-Power Research and Dryden|publisher=NASA|url=http://www.nasa.gov/centers/dryden/news/FactSheets/FS-054-DFRC.html|access-date=30 April 2008}}</ref> The ''[[QinetiQ Zephyr|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.<ref>{{cite web|title=The NASA ERAST HALE UAV Program |publisher=Greg Goebel |url=http://www.vectorsite.net/twuav_15.html#m7 |access-date=30 April 2008 |archive-url=https://web.archive.org/web/20080210021300/http://www.vectorsite.net/twuav_15.html |archive-date=10 February 2008 |url-status=dead }}</ref> From March 2015 to July 2016, [[Solar Impulse]], an [[electric aircraft]], successfully circumnavigated the globe. It is a single-seat plane powered by [[solar cell]]s and capable of taking off under its own power. The design allows the aircraft to remain airborne for several days.<ref>{{cite web|url=http://www.solarimpulse.com/en/documents/hbsia_mission.php?lang=en&group=hbsia |title=HB-SIA Mission |author=Solar Impulse Project |access-date=5 December 2009 |url-status=dead |archive-url=https://web.archive.org/web/20110726022510/http://www.solarimpulse.com/en/documents/hbsia_mission.php?lang=en&group=hbsia |archive-date=26 July 2011 }}</ref>

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.<ref>{{cite web|title=Phenomena which affect a solar balloon|publisher=pagesperso-orange.fr|url=http://pagesperso-orange.fr/ballonsolaire/en-theorie1.htm|access-date=19 August 2008}}</ref>

===Squad Solar vehical===
[[File:Squad Solar Car (Fully Charged 2022).jpg|thumb|[[Squad Solar]]]]
The [[Squad Solar]] is a [[Neighborhood Electric Vehicle]] that has a solar roof and can be plugged into a normal 120 volt outlet to be charged.<ref>{{cite web | url=https://electrek.co/2022/12/06/squad-solar-electric-city-car-coming-to-us-for-6250/ | title=Squad solar electric city car is coming to the US for $6,250 | date=6 December 2022 }}</ref>

==Fuel production==
[[File:Photo of the Week- Boosting Solar Technology (8722948189).jpg|thumb|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.{{Update inline|date=November 2021}}]]
{{Main|Solar chemical|Solar fuel|Artificial photosynthesis}}
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]].<ref>Bolton (1977), p. 1</ref> A variety of fuels can be produced by [[artificial photosynthesis]].<ref>Wasielewski MR Photoinduced electron transfer in supramolecular systems for artificial photosynthesis. Chem. Rev. 1992; 92: 435–61.</ref> 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.<ref>Hammarstrom L. and Hammes-Schiffer S. Artificial Photosynthesis and Solar Fuels. Accounts of Chemical Research 2009; 42 (12): 1859–60.</ref> Some have envisaged working solar fuel plants in coastal metropolitan areas by 2050{{snd}} the splitting of seawater 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.<ref>Gray H.B. Powering the planet with solar fuel. Nature Chemistry 2009; 1: 7.</ref> In addition, chemical energy storage is another solution to solar energy storage.<ref>{{Cite journal |last1=Feng |first1=Hao |last2=Liu |first2=Jian |last3=Zhang |first3=Ying |last4=Liu |first4=Dong |date=2022-06-20 |title=Solar Energy Storage in an All-Vanadium Photoelectrochemical Cell: Structural Effect of Titania Nanocatalyst in Photoanode |journal=Energies |language=en |volume=15 |issue=12 |pages=4508 |doi=10.3390/en15124508 |issn=1996-1073|doi-access=free }}</ref> 

[[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 ({{convert|2300|-|2600|C|disp=or|sigfig=2}}).<ref>Agrafiotis (2005), p. 409</ref> Another approach uses the heat from solar concentrators to drive the [[steam reforming|steam reformation]] of natural gas thereby increasing the overall hydrogen yield compared to conventional reforming methods.<ref>Zedtwitz (2006), p. 1333</ref> 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&nbsp;MW solar furnace to decompose [[zinc oxide]] (ZnO) at temperatures above {{convert|1200|C|sigfig=2}}. This initial reaction produces pure zinc, which can subsequently be reacted with water to produce hydrogen.<ref>{{cite web|title=Solar Energy Project at the Weizmann Institute Promises to Advance the use of Hydrogen Fuel|publisher=Weizmann Institute of Science|url=http://wis-wander.weizmann.ac.il/site/en/weizman.asp?pi=371&doc_id=4210|access-date=25 June 2008|url-status=dead|archive-url=https://web.archive.org/web/20080406124059/http://wis-wander.weizmann.ac.il/site/en/weizman.asp?pi=371&doc_id=4210|archive-date=6 April 2008}}</ref>

==Energy storage methods==
{{Main|Energy storage|Seasonal thermal energy storage|Phase change material|Grid energy storage|Vehicle-to-grid}}
[[File:Andasol 3.jpg|thumb|[[Thermal energy storage]]. The [[Andasol solar power station|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 [[seasonal thermal energy storage|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 [[wikt:off-peak|off-peak]] hours and reduce overall heating and cooling requirements.<ref>Balcomb(1992), p. 6</ref><ref>{{cite web|title=Request for Participation Summer 2005 Demand Shifting with Thermal Mass|publisher=Demand Response Research Center|url=http://www.drrc.lbl.gov/pubs/RFP_071405.pdf|access-date=26 November 2007|url-status=dead|archive-url=https://web.archive.org/web/20080907214724/http://drrc.lbl.gov/pubs/RFP_071405.pdf|archive-date=7 September 2008}}</ref>

Phase change materials such as [[paraffin wax]] and [[Sodium sulfate#Thermal storage|Glauber's salt]] are another thermal storage medium. These materials are inexpensive, readily available, and can deliver domestically useful temperatures (approximately {{convert|64|C|disp=or}}). The "Dover House" (in [[Dover, Massachusetts]]) was the first to use a Glauber's salt heating system, in 1948.<ref>Butti and Perlin (1981), pp. 212–14</ref> Solar energy can also be stored at high temperatures using [[molten salt]]s. 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 [[The Solar Project#Solar Two|Solar Two]] project used this method of energy storage, allowing it to store {{convert|1.44|TJ|lk=in}} in its 68 m³ storage tank with an annual storage efficiency of about 99%.<ref>{{cite web|title=Advantages of Using Molten Salt|publisher=Sandia National Laboratory|url=http://www.sandia.gov/Renewable_Energy/solarthermal/NSTTF/salt.htm|access-date=29 September 2007}}</ref>

Off-grid [[Photovoltaics|PV systems]] have traditionally used [[rechargeable batteries]] to store excess electricity. With grid-tied systems, excess electricity can be sent to the transmission [[Grid-tied electrical system|grid]], while standard grid electricity can be used to meet shortfalls. [[Net metering]] programs give household systems 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.<ref>{{cite web|title=PV Systems and Net Metering |publisher=Department of Energy |url=http://www1.eere.energy.gov/solar/net_metering.html |access-date=31 July 2008 |archive-url=https://web.archive.org/web/20080704062311/http://www1.eere.energy.gov/solar/net_metering.html |archive-date=4 July 2008 |url-status=dead }}</ref> 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.<ref>{{cite web|title=Pumped Hydro Storage |publisher=Electricity Storage Association |url=http://www.electricitystorage.org/tech/technologies_technologies_pumpedhydro.htm |access-date=31 July 2008 |archive-url=https://web.archive.org/web/20080621052054/http://www.electricitystorage.org/tech/technologies_technologies_pumpedhydro.htm |archive-date=21 June 2008 |url-status=dead }}</ref>

==Development, deployment and economics==
[[File:03242012Taller sostenibilidad lore060.jpg|thumb|Participants in a workshop on sustainable development inspect solar panels at [[Monterrey Institute of Technology and Higher Education, Mexico City]] on top of a building on campus.]]{{Further|Deployment of solar power to energy grids}}{{See also|Cost of electricity by source|Renewable energy by country}}
[[File:Solar PV module prices.svg|thumb|Cost development of solar PV modules per watt]]

Beginning with the surge in [[coal]] use, which accompanied the [[Industrial Revolution]], energy consumption steadily transitioned from wood and biomass to [[fossil fuel]]s. 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&nbsp; century in the face of the increasing availability, economy, and utility of coal and [[petroleum]].<ref>Butti and Perlin (1981), pp. 63, 77, 101</ref>

The [[1973 oil crisis|1973 oil embargo]] and [[1979 energy crisis]] caused a reorganization of energy policies around the world. It brought renewed attention to developing solar technologies.<ref>Butti and Perlin (1981), p. 249</ref><ref>Yergin (1991), pp. 634, 653–73</ref> 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 ([[New Energy and Industrial Technology Development Organization|NEDO]]), and [[Solar power in Germany|Germany]] ([[Fraunhofer Society|Fraunhofer Institute for Solar Energy Systems ISE]]).<ref>{{cite web|title=Chronicle of Fraunhofer-Gesellschaft|publisher=Fraunhofer-Gesellschaft|url=http://www.fraunhofer.de/EN/company/profile/chronicle/1972-1982.jsp|access-date=4 November 2007}}</ref>

Commercial solar water heaters began appearing in the United States in the 1890s.<ref>Butti, and Perlin (1981), p. 117</ref> These systems saw increasing use until the 1920s but were gradually replaced by cheaper and more reliable heating fuels.<ref>Butti and Perlin (1981), p. 139</ref> 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.<ref name="SWH 2008">{{cite web|title=Solar Heat Worldwide – Markets and Contribution to the Energy Supply 2006|author=Weiss, Werner|author2=Bergmann, Irene|author3=Faninger, Gerhard|publisher=International Energy Agency|url=http://www.iea-shc.org/data/sites/1/publications/IEA-SHC_Solar_Heat_Worldwide-2008.pdf|access-date=9 June 2008}}</ref> Although generally underestimated, solar water heating and cooling is by far the most widely deployed solar technology with an estimated capacity of 154&nbsp; GW as of 2007.<ref name="SWH 2008"/>

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:<ref name=ie11/>
<blockquote>
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.<ref name=ie11/>
</blockquote>

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]] and [[energy transition|transitioning to renewable energy]]. The energy from the Sun could play a key role in de-carbonizing the global economy alongside improvements in [[Efficient energy use|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".<ref>{{cite web|url=http://www.businessweek.com/news/2011-12-01/iea-says-solar-may-provide-a-third-of-global-energy-by-2060.html|archive-url=https://archive.today/20120721163317/http://www.businessweek.com/news/2011-12-01/iea-says-solar-may-provide-a-third-of-global-energy-by-2060.html|url-status=dead|archive-date=July 21, 2012|title=IEA Says Solar May Provide a Third of Global Energy by 2060|date=1 December 2011|work=Bloomberg Businessweek}}</ref>

{{quote|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]]| ''The New York Times'', 2 July 1916.<ref name="nytimes.com"/>}}In 2021 [[Lazard]] estimated the [[Levelized cost of energy|levelized cost]] of new build unsubsidized utility scale solar electricity at less than 37 dollars per MWh and existing coal-fired power above that amount.<ref name="auto">{{Cite web|title='Renewables' power ahead to become the world's cheapest source of energy in 2020|url=https://www.weforum.org/agenda/2021/07/renewables-cheapest-energy-source/|access-date=2022-01-25|website=World Economic Forum|date=5 July 2021 |language=en}}</ref><ref name=":0">{{Cite web|title=Levelized Cost Of Energy, Levelized Cost Of Storage, and Levelized Cost Of Hydrogen|url=http://www.lazard.com/perspective/levelized-cost-of-energy-levelized-cost-of-storage-and-levelized-cost-of-hydrogen/|access-date=2022-01-25|website=Lazard.com|language=en}}</ref> The 2021 report also said that new solar was also cheaper than new gas-fired power, but not generally existing gas power.<ref name=":0" />

=== Emerging technologies ===
{{see also|Thin-film solar cell}}
[[Image:Best Research-Cell Efficiencies.png|thumb|[[Solar cell efficiencies]] of various cell technologies (including both [[Single-crystal silicon|single-crystal]] and [[Thin-film solar cell|thin film]] technologies) as tracked by [[NREL]]]]
==== Experimental solar power ====
{{main|Solar power#Emerging technologies}}
Concentrated photovoltaics (CPV) systems employ sunlight concentrated onto photovoltaic surfaces for the purpose of electricity generation. [[Thermogenerator|Thermoelectric]], or "thermovoltaic" devices convert a temperature difference between dissimilar materials into an electric current.

==== Floating solar arrays ====
{{Excerpt|Floating solar}}

==== Solar-assisted heat pump ====
{{main|Solar-assisted heat pump}}
A [[heat pump]] is a device that provides heat energy from a source of heat to a destination called a "heat sink". Heat pumps are designed to move [[thermal energy]] opposite to the direction of spontaneous heat flow by absorbing heat from a cold space and releasing it to a warmer one. A solar-assisted heat pump represents the integration of a heat pump and [[Solar thermal collector|thermal solar panels]] in a single integrated system. Typically these two technologies are used separately (or only placing them in parallel) to produce [[Water heating|hot water]].<ref name="ref1">{{cite web |title=Solar-assisted heat pumps |url=http://www.bine.info/en/publications/themeninfos/publikation/elektrisch-angetriebene-waermepumpen/waermepumpen-plus-solar/ |url-status=dead |archive-url=https://web.archive.org/web/20200228222214/http://www.bine.info/en/publications/themeninfos/publikation/elektrisch-angetriebene-waermepumpen/waermepumpen-plus-solar/ |archive-date=28 February 2020 |access-date=21 June 2016}}</ref> In this system the solar thermal panel performs the function of the low temperature heat source and the heat produced is used to feed the heat pump's evaporator.<ref name="ref2">{{cite web |title=Pompe di calore elio-assistite |url=http://www.climatizzazioneconfontirinnovabili.enea.it/index.php/pompe-di-calore-elioassistite |url-status=dead |archive-url=https://web.archive.org/web/20120107065814/http://climatizzazioneconfontirinnovabili.enea.it/index.php/pompe-di-calore-elioassistite |archive-date=7 January 2012 |access-date=21 June 2016 |language=it}}</ref> The goal of this system is to get high [[Coefficient of performance|COP]] and then produce energy in a more [[Energy conversion efficiency|efficient]] and less expensive way.

It is possible to use any type of solar thermal panel (sheet and tubes, roll-bond, heat pipe, thermal plates) or [[Photovoltaic thermal hybrid solar collector|hybrid]] ([[Mono-crystalline silicon|mono]]/[[Polycrystalline silicon|polycrystalline]], [[Thin-film solar cell|thin film]]) in combination with the heat pump. The use of a hybrid panel is preferable because it allows covering a part of the electricity demand of the heat pump and reduces the power consumption and consequently the [[Variable cost|variable costs]] of the system.

==== Solar aircraft ====
[[File:Solar_Impulse_SI2_pilote_Bertrand_Piccard_Payerne_November_2014.jpg|thumb|In 2016, ''[[Solar Impulse 2]]'' was the first [[solar-powered aircraft]] to complete a [[circumnavigation]] of the world.]]
{{see also|Solar Impulse}}
An [[electric aircraft]] is an aircraft that runs on [[Electric motor|electric motors]] rather than [[Internal combustion engine|internal combustion engines]], with electricity coming from [[Fuel cell|fuel cells]], [[Solar cell|solar cells]], [[ultracapacitors]], [[power beaming]],<ref>{{Cite web|url=http://www.dfrc.nasa.gov/gallery/Photo/Power-Beaming/index.html|archiveurl=https://web.archive.org/web/20130217082723/http://www.dfrc.nasa.gov/gallery/photo/Power-Beaming/index.html|url-status=dead|title=Power Beaming|archivedate=February 17, 2013}}</ref> or [[Electric battery|batteries]].

Currently, flying manned electric aircraft are mostly experimental demonstrators, though many small [[Unmanned aerial vehicle|unmanned aerial vehicles]] are powered by batteries. [[Model aircraft#Electric power|Electrically powered model aircraft]] have been flown since the 1970s, with one report in 1957.<ref name="Noth">{{cite web |last=Noth |first=André |date=July 2008 |title=History of Solar Flight |url=http://www.asl.ethz.ch/research/asl/skysailor/History_of_Solar_Flight.pdf |url-status=dead |archive-url=https://web.archive.org/web/20120201032732/http://www.asl.ethz.ch/research/asl/skysailor/History_of_Solar_Flight.pdf |archive-date=1 February 2012 |access-date=8 July 2010 |work=Autonomous Systems Lab |publisher=Swiss Federal Institute of Technology |location=Zürich |page=3 |quote=Günter Rochelt was the designer and builder of Solair I, a 16 m wingspan solar airplane ... 21st of August 1983 he flew in Solair I, mostly on solar energy and also thermals, during 5 hours 41 minutes.}}</ref><ref>{{cite web |date=20 August 2015 |title=Infographic: A Timeline Of The Present And Future Of Electric Flight |url=http://www.popsci.com/infographic-timeline-present-and-future-electric-flight |url-status=live |archive-url=https://web.archive.org/web/20160114043033/http://www.popsci.com/infographic-timeline-present-and-future-electric-flight |archive-date=14 January 2016 |access-date=7 January 2016 |work=Popular Science}}</ref> The first man-carrying electrically powered flights were made in 1973.<ref name="JAWA74">{{cite book |last=Taylor |first=John W R |title=Jane's All the World's Aircraft 1974-75 |publisher=Jane's Yearbooks |year=1974 |isbn=0-354-00502-2 |location=London |page=573}}</ref> Between 2015 and 2016, a manned, solar-powered plane, ''[[Solar Impulse 2]]'', completed a circumnavigation of the Earth.<ref name="Batrawy">{{cite news |author=Batrawy, Aya |date=9 March 2015 |title=Solar-powered plane takes off for flight around the world |agency=Associated Press |url=https://news.yahoo.com/solar-powered-plane-takes-off-flight-around-world-041503078.html |url-status=live |access-date=14 March 2015 |archive-url=https://web.archive.org/web/20160306091406/http://news.yahoo.com/solar-powered-plane-takes-off-flight-around-world-041503078.html |archive-date=6 March 2016}}</ref>

==See also==
{{Portal|Renewable energy|Energy|Technology}}
{{div col|colwidth=22em}}
* [[Heliostat]]
* [[List of solar energy topics]]
* [[List of solar-powered products]]
* [[Renewable heat]]
* [[Soil solarization]]
* [[Solar easement]]
* [[Solar energy use in rural Africa]]
* [[Solar updraft tower]]
* [[Solar power satellite]]
* [[Solar tracker]]
{{div col end}}

==References==
{{Reflist}}

==Further reading==
{{Commons category}}{{Library resources box}}

{{refbegin}}
* {{cite book|last=Denzer |first=Anthony |title=The Solar House: Pioneering Sustainable Design |publisher=Rizzoli |date=2013 |url=http://solarhousehistory.com/book/ |isbn=978-0-8478-4005-2 |url-status=dead |archive-url=https://web.archive.org/web/20130726200811/http://solarhousehistory.com/book/ |archive-date=26 July 2013 }}

{{refend}}

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