Editing Solar energy (section)

== 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=|bibcode=2008WSTec..58..253S }}</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 |bibcode=2003WSTec..48..307T }}</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.