View source for Engineering:Solar power

{{Short description|Conversion of energy from sunlight into electricity}}
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 |caption1=A solar [[Physics:Photovoltaic system|photovoltaic system]] array on a rooftop in [[Place:Hong Kong|Hong Kong]]
 |caption2=The first three [[Engineering:Concentrated solar power|concentrated solar power]] (CSP) units of Spain's [[Engineering:Solnova Solar Power Station|Solnova Solar Power Station]] in the foreground, with the PS10 and PS20 solar power towers in the background
 |caption3=Estimated solar energy available for power generation. The map shows the average daily/yearly sum of electricity production from a 1 kW-peak grid-connected solar PV power plant covering the period from 1994/1999/2007 (depending on the geographical region) to 2018.<ref>{{Cite web |title=Global Solar Atlas |url=https://globalsolaratlas.info/ |access-date=2022-08-12 |website=globalsolaratlas.info}}</ref>
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'''Solar power''', also known as '''solar electricity''', is the conversion of energy from [[Astronomy:Sunlight|sunlight]] into [[Physics:Electricity|electricity]], either directly using [[Chemistry:Photovoltaics|photovoltaics]] (PV) or indirectly using [[Engineering:Concentrated solar power|concentrated solar power]]. Photovoltaic cells convert light into an [[Physics:Electric current|electric current]] using the [[Chemistry:Photovoltaic effect|photovoltaic effect]].<ref>{{cite web |title=Energy Sources: Solar |url=https://www.energy.gov/energysources/solar.htm |url-status=live |archive-url=https://web.archive.org/web/20110414081047/http://www.energy.gov/energysources/solar.htm |archive-date=14 April 2011 |access-date=19 April 2011 |work=Department of Energy |df=dmy-all}}</ref> Concentrated solar power systems use [[Physics:Lens (optics)|lenses]] or mirrors and solar tracking systems to focus a large area of sunlight to a hot spot, often to drive a [[Engineering:Steam turbine|steam turbine]].

Photovoltaics were initially solely used as a source of electricity for small and medium-sized applications, from the [[Engineering:Calculator|calculator]] powered by a single solar cell to remote homes powered by an off-grid rooftop PV system. Commercial concentrated solar power plants were first developed in the 1980s. Since then, as the cost of solar electricity has fallen,  grid-connected solar PV systems' capacity and production have [[Physics:Growth of photovoltaics|grown more or less exponentially]], doubling about every three years. Millions of installations and gigawatt-scale [[Physics:Photovoltaic power station|photovoltaic power station]]s continue to be built, with half of the new generation capacity being solar in 2021.<ref>{{Cite web |title=Power Transition Trends 2022 |url=https://assets.bbhub.io/professional/sites/24/BNEF-Power-Transition-Trends-2022_FINAL.pdf}}</ref>

In 2023, solar generated 5% of the world's electricity,<ref>{{Cite web |title=Executive summary – Renewables 2023 – Analysis |url=https://www.iea.org/reports/renewables-2023/executive-summary |access-date=2024-01-16 |website=IEA |language=en-GB}}</ref> compared to 1% in 2015, when the Paris Agreement to [[Earth:Climate change mitigation|limit climate change]] was signed.<ref name="GER">{{Cite web |date=2022-03-29 |title=Global Electricity Review 2022 |url=https://ember-climate.org/insights/research/global-electricity-review-2022/ |access-date=2022-04-03 |website=Ember |language=en-US}}</ref> Along with onshore wind, in most countries, the cheapest levelised cost of electricity for new installations is utility-scale solar.<ref>{{Cite web |title=2023 Levelized Cost Of Energy+ |url=https://www.lazard.com/research-insights/2023-levelized-cost-of-energyplus/ |access-date=2023-06-14 |website=[[Company:Lazard|Lazard]] |language=en}}</ref><ref>{{Cite web |title=Executive summary – Renewable Energy Market Update - June 2023 – Analysis |url=https://www.iea.org/reports/renewable-energy-market-update-june-2023/executive-summary |access-date=2023-06-14 |website=IEA |language=en-GB}}</ref>

Almost half the solar power installed in 2022 was [[Physics:Rooftop solar power|rooftop]].<ref name=":7">{{Cite web |last=Norman |first=Will |date=2023-06-13 |title=Through the roof: 49.5% of world's PV additions were rooftop in 2022 – SolarPower Europe |url=https://www.pv-tech.org/through-the-roof-49-5-of-worlds-pv-additions-were-rooftop-in-2022-solarpower-europe/ |access-date=2023-06-14 |website=PV Tech |language=en-US}}</ref> Low-carbon power has been recommended as part of a plan to [[Earth:Climate change mitigation|limit climate change]]. The [[Organization:International Energy Agency|International Energy Agency]] said in 2022 that more effort was needed for grid integration and the mitigation of policy, regulation and financing challenges.<ref>{{Cite web |title=Solar PV – Analysis |url=https://www.iea.org/reports/solar-pv |access-date=2022-11-10 |website=IEA |language=en-GB}}</ref>


== Potential ==
{{Sustainable energy}}
Geography affects solar energy potential because different locations receive different amounts of solar radiation. In particular, with some variations, areas that are closer to the [[Astronomy:Equator|equator]] generally receive higher amounts of solar radiation. However, the use of [[Chemistry:Photovoltaics|photovoltaics]] that can follow the position of the Sun can significantly increase the solar energy potential in areas that are farther from the equator.<ref name="World Energy Assessment">{{Cite book |title=World energy assessment: energy and the challenge of sustainability |date=2000 |publisher=United Nations Development Programme |isbn=978-92-1-126126-4 |editor-last=Goldemberg |editor-first=José |edition=1. print |location=New York, NY |editor-last2=UNDP}}</ref> Time variation affects the potential of solar energy, because during the night there is little solar radiation on the surface of the Earth for solar panels to absorb. This limits the amount of energy that solar panels can absorb in one day. [[Earth:Cloud cover|Cloud cover]] can affect the potential of solar panels because clouds block incoming light from the Sun and reduce the light available for solar cells.

Besides, land availability has a large effect on the available solar energy because solar panels can only be set up on land that is otherwise unused and suitable for solar panels. Roofs are a suitable place for solar cells, as many people have discovered that they can collect energy directly from their homes this way. Other areas that are suitable for solar cells are lands that are not being used for businesses, where solar plants can be established.<ref name="World Energy Assessment" />

== Technologies ==

Solar power plants use one of two technologies:
* Photovoltaic (PV) systems use [[Physics:Solar panel|solar panel]]s, either on [[Physics:Rooftop photovoltaic power station|rooftops]] or in ground-mounted solar farms, converting sunlight directly into electric power. 
* [[Engineering:Concentrated solar power|Concentrated solar power]] (CSP) uses mirrors or lenses to concentrate sunlight to extreme heat to eventually make steam, which is converted into electricity by a [[Engineering:Steam turbine|turbine]].

=== Photovoltaic cells ===
{{Main|Chemistry:Photovoltaics|Physics:Solar cell}}
[[File:PV-system-schematics-residential-Eng.png|thumb|upright=1.4|Schematics of a grid-connected residential PV power system<ref name="SolarCells_Section10_2">Solar Cells and their Applications Second Edition, Lewis Fraas, Larry Partain, Wiley, 2010, {{ISBN|978-0-470-44633-1}}, Section10.2.</ref>]]

A [[Physics:Solar cell|solar cell]], or photovoltaic cell, is a device that converts light into electric current using the [[Chemistry:Photovoltaic effect|photovoltaic effect]]. The first solar cell was constructed by Charles Fritts in the 1880s.<ref>{{harvnb|Perlin|1999|p = 147}}</ref> The German industrialist Ernst Werner von Siemens was among those who recognized the importance of this discovery.<ref>{{harvnb|Perlin|1999|pp = 18-20}}</ref> In 1931, the German engineer Bruno Lange developed a photo cell using [[Chemistry:Silver selenide|silver selenide]] in place of [[Chemistry:Copper oxide|copper oxide]],<ref>{{cite journal|url=https://archive.org/details/bub_gb_9CcDAAAAMBAJ |page=[https://archive.org/details/bub_gb_9CcDAAAAMBAJ/page/n42 41] |title=Magic Plates, Tap Sun For Power|journal=Popular Science |date = June 1931|access-date=19 April 2011|last1=Corporation|first1=Bonnier}}</ref> although the prototype [[Chemistry:Selenium|selenium]] cells converted less than 1% of incident light into electricity. Following the work of Russell Ohl in the 1940s, researchers Gerald Pearson, Calvin Fuller and Daryl Chapin created the [[Chemistry:Silicon|silicon]] solar cell in 1954.<ref>{{harvnb|Perlin|1999|p = 29}}</ref> These early solar cells cost US$286/watt and reached efficiencies of 4.5–6%.<ref>{{harvnb|Perlin|1999|pp = 29-30,38}}</ref> In 1957, Mohamed M. Atalla developed the process of silicon [[Engineering:Surface passivation|surface passivation]] by [[Physics:Thermal oxidation|thermal oxidation]] at [[Organization:Bell Labs|Bell Labs]].<ref>{{cite book |last1=Black |first1=Lachlan E. |title=New Perspectives on Surface Passivation: Understanding the Si-Al2O3 Interface |date=2016 |publisher=Springer |isbn=9783319325217 |url=https://core.ac.uk/download/pdf/156698511.pdf |page=13}}</ref><ref name="Lojek">{{cite book |last1=Lojek |first1=Bo |title=History of Semiconductor Engineering |url=https://archive.org/details/historysemicondu00loje_697 |url-access=limited |date=2007 |publisher=Springer Science & Business Media |isbn=9783540342588 |pages=[https://archive.org/details/historysemicondu00loje_697/page/n128 120]& 321–323}}</ref> The surface passivation process has since been critical to [[Physics:Solar cell efficiency|solar cell efficiency]].<ref>{{cite book |last1=Black |first1=Lachlan E. |title=New Perspectives on Surface Passivation: Understanding the Si-Al2O3 Interface |date=2016 |publisher=Springer |isbn=9783319325217 |url=https://core.ac.uk/download/pdf/156698511.pdf}}</ref>

{{As of|2022}} over 90% of the market is [[Chemistry:Crystalline silicon|crystalline silicon]].<ref name=":5" /> The array of a photovoltaic system, or PV system, produces [[Physics:Direct current|direct current]] (DC) power which fluctuates with the sunlight's intensity. For practical use this usually requires conversion to [[Physics:Alternating current|alternating current]] (AC), through the use of [[Physics:Solar inverter|inverters]].<ref name="SolarCells_Section10_2" /> Multiple solar cells are connected inside panels. Panels are wired together to form arrays, then tied to an inverter, which produces power at the desired voltage, and for AC, the desired frequency/phase.<ref name="SolarCells_Section10_2" />

Many residential PV systems are connected to the grid wherever available, especially in developed countries with large markets.<ref name="IEAPVPS2009_Fig3">{{cite web | url=http://www.iea-pvps.org/index.php?id=92&eID=dam_frontend_push&docID=432 | title=Trends in Photovoltaic Applications Survey report of selected IEA countries between 1992 and 2009, IEA-PVPS | access-date=8 November 2011 | url-status=live | archive-url=https://web.archive.org/web/20170525165534/http://www.iea-pvps.org/index.php?id=92&eID=dam_frontend_push&docID=432 | archive-date=25 May 2017 | df=dmy-all }}</ref> 
In these grid-connected PV systems, use of energy storage is optional. 
In certain applications such as satellites, lighthouses, or in developing countries, batteries or additional power generators are often added as back-ups. Such [[Engineering:Stand-alone power system|stand-alone power system]]s permit operations at night and at other times of limited sunlight.

In "vertical agrivoltaics" system, solar cells are oriented vertically on farmland, to allow the land to both grow crops and generate renewable energy.<ref name=Cooldown_20240117/> Other configurations include floating solar farms, placing solar canopies over parking lots, and installing solar panels on roofs.<ref name=Cooldown_20240117>{{cite news |last1=Budin |first1=Jeremiah |title=Game-Changing Solar Power Technology to Get First US Installation: Valuable Land is almost Completely Preserved |url=https://www.thecooldown.com/green-tech/vertical-agrivoltaics-vermont-solar-farm/ |work=The Cooldown |date=17 January 2024 |archive-url=https://web.archive.org/web/20240117053018/https://www.thecooldown.com/green-tech/vertical-agrivoltaics-vermont-solar-farm/ |archive-date=17 January 2024}}</ref>

====Thin-film solar====
{{main|Engineering:Thin-film solar cell}}
A [[Engineering:Thin-film solar cell|thin-film solar cell]] is a second generation [[Physics:Solar cell|solar cell]] that is made by depositing one or more thin layers, or [[Physics:Thin film|thin film]] (TF) of photovoltaic material on a substrate, such as glass, plastic or metal. Thin-film solar cells are commercially used in several technologies, including [[Physics:Cadmium telluride photovoltaics|cadmium telluride]] (CdTe), [[Physics:Copper indium gallium selenide solar cells|copper indium gallium diselenide]] (CIGS), and [[Chemistry:Amorphous silicon|amorphous thin-film silicon]] (a-Si, TF-Si).<ref>{{cite web | url=https://ases.org/thin-film-solar-panels/ | title=Thin-Film Solar Panels &#124; American Solar Energy Society }}</ref>

==== Perovskite solar cells ====
{{Excerpt|Perovskite solar cell|paragraphs=1,2|file=yes}}

=== Concentrated solar power ===
[[File:Parabolic trough.svg|thumb|A [[Engineering:Parabolic trough|parabolic collector]] concentrates sunlight onto a tube in its focal point.]]
{{Main|Engineering:Concentrated solar power}}

[[Engineering:Concentrated solar power|Concentrated solar power]] (CSP), also called "concentrated solar thermal", uses lenses or mirrors and tracking systems to concentrate sunlight, then use the resulting heat to generate electricity from conventional steam-driven turbines.<ref>{{cite web |date=2018-06-11 |title=How CSP Works: Tower, Trough, Fresnel or Dish |url=https://www.solarpaces.org/how-csp-works/ |access-date=2020-03-14 |website=Solarpaces |language=en-US}}</ref>

A wide range of concentrating technologies exists among the best known are the [[Engineering:Parabolic trough|parabolic trough]], the [[Engineering:Compact linear Fresnel reflector|compact linear Fresnel reflector]], the dish Stirling and the [[Engineering:Solar power tower|solar power tower]]. Various techniques are used to track the sun and focus light. In all of these systems a [[Physics:Working fluid|working fluid]] is heated by the concentrated sunlight and is then used for power generation or energy storage.<ref name="Martin 2005">Martin and Goswami (2005), p. 45</ref> Thermal storage efficiently allows overnight electricity generation,<ref>{{cite web|url=http://www.renewableenergyworld.com/rea/news/article/2011/07/solar-can-be-baseload-spanish-csp-plant-with-storage-produces-electricity-for-24-hours-straight|title=Spanish CSP Plant with Storage Produces Electricity for 24 Hours Straight|author=Stephen Lacey|date=6 July 2011|url-status=live|archive-url=https://web.archive.org/web/20121012112224/http://www.renewableenergyworld.com/rea/news/article/2011/07/solar-can-be-baseload-spanish-csp-plant-with-storage-produces-electricity-for-24-hours-straight|archive-date=12 October 2012|df=dmy-all}}</ref> thus complementing PV.<ref>{{Cite news |date=2022-10-05 |title=More countries are turning to this technology for clean energy. It's coming to Australia |language=en-AU |work=ABC News |url=https://www.abc.net.au/news/2022-10-06/concentrated-solar-thermal-in-queensland-renewable-strategy/101502426 |access-date=2022-11-04}}</ref> CSP generates a very small share of solar power and in 2022 the [[Organization:International Energy Agency|IEA]] said that CSP should be better paid for its storage.<ref>{{Cite web |title=Renewable Electricity – Analysis |url=https://www.iea.org/reports/renewable-electricity |access-date=2022-11-04 |website=IEA |language=en-GB}}</ref>

{{As of|2021}} the levelized cost of electricity from CSP is over twice that of PV.<ref>{{Cite web |title=Renewable Power Generation Costs in 2021 |url=https://irena.org/publications/2022/Jul/Renewable-Power-Generation-Costs-in-2021 |access-date=2022-11-04 |website=irena.org |date=13 July 2022 |language=en}}</ref> However, their very high temperatures may prove useful to help decarbonize industries (perhaps via hydrogen) which need to be hotter than electricity can provide.<ref>{{Cite web |last=Casey |first=Tina |date=2022-09-30 |title=US Energy Dept. Still Holds Torch For Concentrating Solar Power |url=https://cleantechnica.com/2022/09/30/us-energy-dept-still-holds-torch-for-concentrating-solar-power/ |access-date=2022-11-04 |website=CleanTechnica |language=en-US}}</ref>

=== Hybrid systems ===
{{Main|Chemistry:Hybrid power}}

A hybrid system combines solar with energy storage and/or one or more other forms of generation. Hydro,<ref>{{Cite web |last=Garanovic |first=Amir |date=2021-11-10 |title=World's largest hydro-floating solar hybrid comes online in Thailand |url=https://www.offshore-energy.biz/worlds-largest-hydro-floating-solar-hybrid-comes-online-in-thailand/ |access-date=2022-11-07 |website=Offshore Energy |language=en-US}}</ref><ref>{{Citation |last1=Ming |first1=Bo |title=Chapter 20 - Operations management of large hydro–PV hybrid power plants: case studies in China |date=2022-01-01 |url=https://www.sciencedirect.com/science/article/pii/B978032385527300008X |work=Complementarity of Variable Renewable Energy Sources |pages=439–502 |editor-last=Jurasz |editor-first=Jakub |publisher=Academic Press |language=en |isbn=978-0-323-85527-3 |access-date=2022-11-07 |last2=Liu |first2=Pan |last3=Guo |first3=Yi |editor2-last=Beluco |editor2-first=Alexandre}}</ref> wind<ref>{{Cite web |title=World's largest wind-solar hybrid complex goes online in India |url=https://renewablesnow.com/news/worlds-largest-wind-solar-hybrid-complex-goes-online-in-india-799667/ |access-date=2022-11-07 |website=Renewablesnow.com |language=en}}</ref><ref>{{Cite web |last=Todorović |first=Igor |date=2022-11-04 |title=China completes world's first hybrid offshore wind-solar power plant |url=https://balkangreenenergynews.com/china-completes-worlds-first-hybrid-offshore-wind-solar-power-plant/ |access-date=2022-11-07 |website=Balkan Green Energy News |language=en-US}}</ref> and batteries<ref>{{Cite web |last=Which? |title=Solar panel battery storage |url=https://www.which.co.uk/reviews/solar-panels/article/solar-panels/solar-panel-battery-storage-a2AfJ0s5tCyT |access-date=2022-11-07 |website=Which? |language=en}}</ref> are commonly combined with solar. The combined generation may enable the system to vary power output with demand, or at least smooth the solar power fluctuation.<ref>{{Cite journal |last1=Brumana |first1=Giovanni |last2=Franchini |first2=Giuseppe |last3=Ghirardi |first3=Elisa |last4=Perdichizzi |first4=Antonio |date=2022-05-01 |title=Techno-economic optimization of hybrid power generation systems: A renewables community case study |url=https://www.sciencedirect.com/science/article/pii/S0360544222003309 |journal=Energy |language=en |volume=246 |pages=123427 |doi=10.1016/j.energy.2022.123427 |s2cid=246695199 |issn=0360-5442}}</ref><ref>{{Cite journal |last1=Wang |first1=Zhenni |last2=Wen |first2=Xin |last3=Tan |first3=Qiaofeng |last4=Fang |first4=Guohua |last5=Lei |first5=Xiaohui |last6=Wang |first6=Hao |last7=Yan |first7=Jinyue |date=2021-08-01 |title=Potential assessment of large-scale hydro-photovoltaic-wind hybrid systems on a global scale |url=https://www.sciencedirect.com/science/article/pii/S1364032121004433 |journal=Renewable and Sustainable Energy Reviews |language=en |volume=146 |pages=111154 |doi=10.1016/j.rser.2021.111154 |s2cid=235925315 |issn=1364-0321}}</ref> There is a lot of hydro worldwide, and adding solar panels on or around existing hydro reservoirs is particularly useful, because hydro is usually more flexible than wind and cheaper at scale than batteries,<ref>{{Cite web |last=Todorović |first=Igor |date=2022-07-22 |title=Portugal, Switzerland launch pumped storage hydropower plants of over 2 GW in total |url=https://balkangreenenergynews.com/portugal-switzerland-launch-pumped-storage-hydropower-plants-of-over-2-gw-in-total/ |access-date=2022-11-08 |website=Balkan Green Energy News |language=en-US}}</ref> and existing power lines can sometimes be used.<ref>{{Cite web |last=Bank (ADB) |first=Asian Development |title=ADB Partnership Report 2019: Building Strong Partnerships for Shared Progress |url=https://www.adb.org/multimedia/partnership-report2019/stories/solar-power-meets-hydropower/ |access-date=2022-11-07 |website=Asian Development Bank |language=en-US}}</ref><ref>{{Cite web |last1=Merlet |first1=Stanislas |last2=Thorud |first2=Bjørn |date=2020-11-18 |title=Floating solar power connected to hydropower might be the future for renewable energy |url=https://sciencenorway.no/hydropower-opinion-renewable-energy/floating-solar-power-connected-to-hydropower-might-be-the-future-for-renewable-energy/1772215 |access-date=2022-11-07 |website=sciencenorway.no}}</ref>

== Development and deployment ==
[[File:Share-electricity-solar.svg|thumb|upright=1.35|The share of electricity production from solar, 2022<ref>{{cite web |title=Share of electricity production from solar |url=https://ourworldindata.org/grapher/share-electricity-solar |website=Our World in Data |access-date=15 August 2023}}</ref>]]
[[File:World solar generation yearly.png |thumb|upright=1.35| Yearly solar generation by continent]]
[[File:2007- New solar installations - annually by country or region.svg |thumb |upright=1.35 |Benefitting from favorable policies and declining costs of modules, photovoltaic solar installation has grown consistently, with China expected to account for 50% of new global solar photovoltaic projects by 2024.<ref name=Canary_BloombergNEF_20230915>{{cite web |title=Chart: Solar installations set to break global, US records in 2023 |url=https://www.canarymedia.com/articles/solar/chart-solar-installations-set-to-break-global-us-records-in-2023 |publisher=Canary Media |archive-url=https://web.archive.org/web/20230917103745/https://www.canarymedia.com/articles/solar/chart-solar-installations-set-to-break-global-us-records-in-2023 |archive-date=17 September 2023 |date=15 September 2023 |url-status=live }} For relevant chart, Canary Media credits: "Source: BloombergNEF, September 2023"</ref><ref name=BNEF_20230905>{{cite web |last1=Chase |first1=Jenny |title=3Q 2023 Global PV Market Outlook |url=https://about.bnef.com/blog/3q-2023-global-pv-market-outlook/ |publisher=BloombergNEF |archive-url=https://web.archive.org/web/20230921083709/https://about.bnef.com/blog/3q-2023-global-pv-market-outlook/ |archive-date=21 September 2023 |date=5 September 2023 |url-status=live }}</ref>]]
[[File:Installed_solar_PV_capacity_log_graph.svg |thumb |upright=1.35 |The growth of solar PV on a semi-log scale since 1996]]
[[File:Electricity production by source.svg |thumb |upright=1.35 |Electricity production by source]]

=== Early days ===

The early development of solar technologies starting in the 1860s was driven by an expectation that coal would soon become scarce, such as experiments by Augustin Mouchot.<ref>{{Cite book|url=https://books.google.com/books?id=RmM9AQAAIAAJ&q=carbonic+oxide|title=Scientific American|date=1869-04-10|publisher=Munn & Company|pages=227|language=en}}</ref> Charles Fritts installed the world's first rooftop photovoltaic solar array, using 1%-efficient [[Chemistry:Selenium|selenium]] cells, on a New York City roof in 1884.<ref>{{cite web|url=https://cleantechnica.com/2014/12/31/photovoltaic-dreaming-first-attempts-commercializing-pv/|title=Photovoltaic Dreaming 1875--1905: First Attempts At Commercializing PV - CleanTechnica|date=31 December 2014|website=cleantechnica.com|access-date=30 April 2018|url-status=live|archive-url=https://wayback.archive-it.org/all/20170525170459/https://cleantechnica.com/2014/12/31/photovoltaic-dreaming-first-attempts-commercializing-pv/|archive-date=25 May 2017|df=dmy-all}}</ref> 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 [[Chemistry:Petroleum|petroleum]].<ref>Butti and Perlin (1981), p. 63, 77, 101</ref> Bell Telephone Laboratories’ 1950s research used silicon wafers with a very thin coating of boron. The “Bell Solar Battery” was described as 6% efficient, with a square yard of the panels generating 50 watts.<ref>”The Bell Solar Battery” (advertisement). Audio, July 1964, 15.</ref> The first satellite with solar panels [[Engineering:Vanguard 1|was launched in 1957]].<ref name="NRL">{{cite web |url=http://code8100.nrl.navy.mil/about/heritage/vanguard.htm |title=Vanguard I The World's Oldest Satellite Still in Orbit |archive-url=https://web.archive.org/web/20150321054447/http://code8100.nrl.navy.mil/about/heritage/vanguard.htm |archive-date=2015-03-21|access-date=September 24, 2007}} {{PD-notice}}</ref>

By the 1970s, solar power was being used on satellites, but the cost of solar power was considered to be unrealistic for conventional applications.<ref name="Levy">{{cite journal |last1=Levy |first1=Adam |title=The dazzling history of solar power |journal=Knowable Magazine |date=13 January 2021 |doi=10.1146/knowable-011321-1 |s2cid=234124275 |url=https://knowablemagazine.org/article/technology/2021/the-dazzling-history-solar-power |access-date=25 March 2022 |language=en|doi-access=free }}</ref> In 1974 it was estimated that only six private homes in all of North America were entirely heated or cooled by functional solar power systems.<ref>"The Solar Energy Book-Once More." ''Mother Earth News'' 31:16–17, Jan. 1975</ref> However, the [[Finance:1973 oil crisis|1973 oil embargo]] and 1979 energy crisis caused a reorganization of energy policies around the world and brought renewed attention to developing solar technologies.<ref>Butti and Perlin (1981), p. 249</ref><ref>Yergin (1991), pp. 634, 653–673</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 United States (SERI, now NREL), Japan (NEDO), and Germany (Fraunhofer 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 | url-status=live | archive-url=https://web.archive.org/web/20071212091650/http://www.fraunhofer.de/EN/company/profile/chronicle/1972-1982.jsp | archive-date=12 December 2007 | df=dmy-all }}</ref> Between 1970 and 1983 installations of photovoltaic systems grew rapidly. In the United States, President [[Biography:Jimmy Carter|Jimmy Carter]] set a target of producing 20% of U.S. energy from solar by the year 2000, but his successor, Ronald Reagan, removed the funding for research into renewables.<ref name="Levy"/> Falling oil prices in the early 1980s moderated the [[Physics:Growth of photovoltaics|growth of photovoltaics]] from 1984 to 1996.

=== Mid-1990s to 2010 ===

In the mid-1990s development of both, residential and commercial rooftop solar as well as utility-scale [[Physics:Photovoltaic power station|photovoltaic power station]]s began to accelerate again due to supply issues with oil and natural gas, [[Earth:Climate change|global warming]] concerns, and the improving economic position of PV relative to other energy technologies.<ref name="Levy"/><ref>[http://www.solardev.com/SEIA-lightworld.php Solar: photovoltaic: Lighting Up The World] retrieved 19 May 2009 {{webarchive |url=https://web.archive.org/web/20100813163816/http://www.solardev.com/SEIA-lightworld.php |date=13 August 2010 }}</ref> In the early 2000s, the adoption of feed-in tariffs—a policy mechanism, that gives renewables priority on the grid and defines a fixed price for the generated electricity—led to a high level of investment security and to a soaring number of PV deployments in Europe.

=== 2010s ===
For several years, worldwide growth of solar PV was driven by European deployment, but it has since shifted to Asia, especially China and Japan, and to a growing number of countries and regions all over the world. The largest manufacturers of solar equipment were based in China.<ref>{{cite web|url=http://www.pv-tech.org/editors-blog/45754|title=Top-10 solar cell producers in 2016|first=Finlay|last=Colville|work=PV-Tech|date=30 January 2017|url-status=live|archive-url=https://web.archive.org/web/20170202054912/http://www.pv-tech.org/editors-blog/45754|archive-date=2 February 2017|df=dmy-all}}</ref><ref>{{cite web|url=https://www-cdn.law.stanford.edu/wp-content/uploads/2017/03/Executive-Summary-The-New-Solar-System-1.pdf|title=The New Solar System - Executive Summary|last=Ball|first=Jeffrey |display-authors=0 |date=2017-03-21|website=Stanford University Law School, Steyer-Taylor Center for Energy Policy and Finance|access-date=2017-06-27|url-status=live|archive-url=https://web.archive.org/web/20170420151310/https://www-cdn.law.stanford.edu/wp-content/uploads/2017/03/Executive-Summary-The-New-Solar-System-1.pdf|archive-date=20 April 2017|df=dmy-all}}</ref> Although concentrated solar power capacity grew more than tenfold, it remained a tiny proportion of the total,<ref name="ren21-gsr-2014">
{{cite web |url=http://www.ren21.net/Portals/0/documents/Resources/GSR/2014/GSR2014_full%20report_low%20res.pdf |title=Renewables 2014: Global Status Report |author=REN21 | archive-url= https://web.archive.org/web/20140915214208/http://www.ren21.net/Portals/0/documents/Resources/GSR/2014/GSR2014_full%20report_low%20res.pdf |archive-date=15 September 2014 |year=2014 

=== 2020s ===
Despite the rising cost of materials, such as polysilicon, during the 2021–2022 global energy crisis,<ref>{{Cite web |title=What is the impact of increasing commodity and energy prices on solar PV, wind and biofuels? – Analysis |url=https://www.iea.org/articles/what-is-the-impact-of-increasing-commodity-and-energy-prices-on-solar-pv-wind-and-biofuels |access-date=2022-04-04 |website=IEA |language=en-GB}}</ref> utility scale solar was still the cheapest energy source in many countries due to the rising costs of other energy sources, such as natural gas.<ref>{{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=2022-04-04 |website=Lazard.com |language=en}}</ref> In 2022, global solar generation capacity exceeded 1 TW for the first time.<ref>{{cite web | url=https://www.solarpowereurope.org/press-releases/world-installs-a-record-168-gw-of-solar-power-in-2021-enters-solar-terawatt-age | title=World Installs a Record 168 GW of Solar Power in 2021, enters Solar Terawatt Age - SolarPower Europe }}</ref> However, [[Finance:Fossil fuel subsidies|fossil-fuel subsidies]] have slowed the growth of solar generation capacity.<ref>{{Cite web |last=McDonnell |first=Tim |date=2022-08-29 |title=Soaring fossil fuel subsidies are holding back clean energy |url=https://qz.com/soaring-fossil-fuel-subsidies-are-holding-back-clean-en-1849467945 |access-date=2022-09-04 |website=Quartz |language=en}}</ref>

=== Current status ===
About half of installed capacity is utility scale.<ref name=":2">{{Cite web |author1=Dana Olson |author2=Bent Erik Bakken |publisher=Det Norske Veritas |title=Utility-scale solar PV: From big to biggest |url=https://www.dnv.com/feature/utility-scale-solar.html |access-date=2024-01-15}}</ref>

=== Forecasts ===
[[File:Reality versus IEA predictions - annual photovoltaic additions 2002-2016.png|thumb|Actual annual deployments of solar PV vs predictions by the IEA for the period 2002–2016. Predictions have largely and consistently underestimated actual growth.]]
Most new renewable capacity between 2022 and 2027 is forecast to be solar, surpassing coal as the largest source of installed power capacity.<ref name=":4">{{Cite web |title=Renewable electricity – Renewables 2022 – Analysis |url=https://www.iea.org/reports/renewables-2022/renewable-electricity |access-date=2022-12-12 |website=IEA |language=en-GB}}</ref>{{Rp|page=26}} Utility scale is forecast to become the largest source of electricity in all regions except [[Place:Sub-Saharan Africa|sub-Saharan Africa]] by 2050.<ref name=":2" />

According to a 2021 study, global electricity generation potential of [[Physics:Rooftop solar power|rooftop solar]] panels is estimated at 27 PWh per year at costs ranging from $40 (Asia) to $240 per MWh (US, Europe). Its practical realization will however depend on the availability and cost of scalable electricity storage solutions.<ref>{{Cite web|last=Cork|first=University College|title=Assessing global electricity generation potential from rooftop solar photovoltaics|url=https://techxplore.com/news/2021-10-global-electricity-potential-rooftop-solar.html|access-date=2021-10-11|website=techxplore.com|language=en}}</ref>

=== Photovoltaic power stations ===
{{Excerpt|Photovoltaic power station}}

=== Concentrating solar power stations ===
[[File:IvanpahRunning.JPG|thumb|Ivanpah Solar Electric Generating System with all three towers under load during February 2014, with the Clark Mountain Range seen in the distance]]
[[File:Solar Plant kl.jpg|thumb|Part of the 354 MW [[Engineering:Solar Energy Generating Systems|Solar Energy Generating Systems]] (SEGS) parabolic trough solar complex in northern San Bernardino County, California ]]
Commercial concentrating solar power (CSP) plants, also called "solar thermal power stations", were first developed in the 1980s. The 377&nbsp; MW [[Organization:Ivanpah Solar Power Facility|Ivanpah Solar Power Facility]], located in California's Mojave Desert, is the world's largest solar thermal power plant project. Other large CSP plants include the [[Engineering:Solnova Solar Power Station|Solnova Solar Power Station]] (150&nbsp;MW), the Andasol solar power station (150&nbsp;MW), and [[Engineering:Extresol Solar Power Station|Extresol Solar Power Station]] (150&nbsp;MW), all in Spain. The principal advantage of CSP is the ability to efficiently add thermal storage, allowing the dispatching of electricity over up to a 24-hour period. Since peak electricity demand typically occurs at about 5&nbsp;pm, many CSP power plants use 3 to 5&nbsp;hours of thermal storage.<ref>[http://www.energex.com.au/sustainability/sustainability-rewards-programs/what-is-peak-demand What is peak demand?] {{webarchive|url=https://web.archive.org/web/20120811072202/http://www.energex.com.au/sustainability/sustainability-rewards-programs/what-is-peak-demand |date=11 August 2012 }}, Energex.com.au website.</ref>

== Economics ==

=== Cost per watt ===
The typical cost factors for solar power include the costs of the modules, the frame to hold them, wiring, inverters, labour cost, any land that might be required, the grid connection, maintenance and the solar insolation that location will receive.

Photovoltaic systems use no fuel, and modules typically last 25 to 40 years.<ref>{{Cite journal |last1=Nian |first1=Victor |last2=Mignacca |first2=Benito |last3=Locatelli |first3=Giorgio |date=2022-08-15 |title=Policies toward net-zero: Benchmarking the economic competitiveness of nuclear against wind and solar energy |url=https://www.sciencedirect.com/science/article/pii/S0306261922006328 |journal=Applied Energy |language=en |volume=320 |pages=119275 |doi=10.1016/j.apenergy.2022.119275 |bibcode=2022ApEn..32019275N |s2cid=249223353 |issn=0306-2619}}</ref> Thus upfront capital and financing costs make up 80 to 90% of the cost of solar power.<ref name=":4" />{{Rp|page=165}}

Some countries are considering [[Finance:Price ceiling|price caps]],<ref>{{Cite web |date=2022-09-14 |title=EU expects to raise €140bn from windfall tax on energy firms |url=https://www.theguardian.com/business/2022/sep/14/eu-windfall-tax-energy-fossil-fuel-firms |access-date=2022-09-15 |website=the Guardian |language=en}}</ref> whereas others prefer [[Finance:Contract for difference|contracts for difference]].<ref>{{Cite web |date=2022-09-14 |title=The EU's energy windfall tax gives UK ministers a yardstick for their talks |url=https://www.theguardian.com/business/nils-pratley-on-finance/2022/sep/14/eu-energy-windfall-tax-uk-government-negotiations |access-date=2022-09-15 |website=the Guardian |language=en}}</ref>

The large magnitude of solar energy available makes it a highly appealing source of electricity. In 2020, solar energy was the cheapest source of electricity.<ref name="auto2">{{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=":02">{{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> In Saudi Arabia, a power purchase agreement (PPA) was signed in April 2021 for a new solar power plant in Al-Faisaliah. The project has recorded the world's lowest cost for solar PV electricity production of USD 1.04 cents/ kWh.<ref name="ppa for 2970MW">{{Cite web |date=8 April 2021 |title=Saudi Arabia signed Power Purchase Agreement for 2,970MW Solar PV Projects |url=https://www.saudigulfprojects.com/2021/04/saudi-arabia-signed-power-purchase-agreement-for-2970mw-solar-pv-projects/ |access-date=2022-08-28 |website=saudigulfprojects.com |language=en}}</ref>

=== Installation prices ===
Expenses of high-power band solar modules has greatly decreased over time. Beginning in 1982, the cost per kW was approximately 27,000 American dollars, and in 2006 the cost dropped to approximately 4,000 American dollars per kW. The PV system in 1992 cost approximately 16,000 American dollars per kW and it dropped to approximately 6,000 American dollars per kW in 2008.<ref name="timilsina_solar_2012">{{Cite journal |last1=Timilsina |first1=Govinda R. |last2=Kurdgelashvili |first2=Lado |last3=Narbel |first3=Patrick A. |date=2012-01-01 |title=Solar energy: Markets, economics and policies |url=https://www.sciencedirect.com/science/article/pii/S1364032111004199 |journal=Renewable and Sustainable Energy Reviews |language=en |volume=16 |issue=1 |pages=449–465 |doi=10.1016/j.rser.2011.08.009 |issn=1364-0321}}</ref>

In 2021 in the US, residential solar cost from 2 to 4 dollars/watt (but solar shingles cost much more)<ref>{{Cite web|date=2021-08-08|title=Solar Shingles Vs. Solar Panels: Cost, Efficiency & More (2021)|url=https://www.ecowatch.com/solar-roof-shingles-2654521594.html|access-date=2021-08-25|website=EcoWatch|language=en}}</ref> and utility solar costs were around $1/watt.<ref>{{Cite web|date=2021-06-18|title=Solar Farms: What Are They and How Much Do They Cost? {{!}} EnergySage|url=https://news.energysage.com/solar-farms-start-one/|access-date=2021-08-25|website=Solar News|language=en-US}}</ref>

===Productivity by location===
The productivity of solar power in a region depends on [[Astronomy:Solar irradiance|solar irradiance]], which varies through the day and year and is influenced by [[Earth:Latitude|latitude]] and [[Earth:Climate|climate]]. [[Chemistry:Photovoltaics|PV]] system output power also depends on ambient temperature, wind speed, solar spectrum, the local [[Astronomy:Soiling (solar energy)|soiling]] conditions, and other factors.

Onshore wind power tends to be the cheapest source of electricity in Northern Eurasia, Canada, some parts of the United States, and [[Place:Patagonia|Patagonia]] in Argentina: whereas in other parts of the world mostly solar power (or less often a combination of wind, solar and other low carbon energy) is thought to be best.<ref name="ReferenceA">{{Cite journal |last1=Bogdanov |first1=Dmitrii |last2=Ram |first2=Manish |last3=Aghahosseini |first3=Arman |last4=Gulagi |first4=Ashish |last5=Oyewo |first5=Ayobami Solomon |last6=Child |first6=Michael |last7=Caldera |first7=Upeksha |last8=Sadovskaia |first8=Kristina |last9=Farfan |first9=Javier |last10=De Souza Noel Simas Barbosa |first10=Larissa |last11=Fasihi |first11=Mahdi |date=2021-07-15 |title=Low-cost renewable electricity as the key driver of the global energy transition towards sustainability |journal=Energy |language=en |volume=227 |pages=120467 |doi=10.1016/j.energy.2021.120467 |s2cid=233706454 |issn=0360-5442|doi-access=free }}</ref>{{Rp|page=8}} Modelling by Exeter University suggests that by 2030 solar will be cheapest in all countries except for some in north-east Europe.<ref>{{Cite web |title=Is a solar future inevitable? |url=https://www.exeter.ac.uk/media/universityofexeter/globalsystemsinstitute/documents/GSI_working_papers_solar_August.pdf |access-date=2 October 2023 |website=University of Exeter}}</ref>

The locations with highest annual solar irradiance lie in the arid tropics and subtropics. Deserts lying in low latitudes usually have few clouds and can receive sunshine for more than ten hours a day.<ref>{{cite web |url=http://slideplayer.com/slide/7652063/25/images/3/Daytime+Cloud+Fraction+Coast+lines+evident.jpg |title=Daytime Cloud Fraction Coast lines evident |access-date=2017-08-22 |url-status=live |archive-url=https://web.archive.org/web/20170822174443/http://slideplayer.com/slide/7652063/25/images/3/Daytime+Cloud+Fraction+Coast+lines+evident.jpg |archive-date=22 August 2017 |df=dmy-all }}</ref><ref>{{cite web |url=http://www.econet.org.uk/weather/sun.html |title=Sunshine |access-date=2015-09-06 |url-status=dead |archive-url=https://web.archive.org/web/20150923233148/http://www.econet.org.uk/weather/sun.html |archive-date=23 September 2015 |df=dmy-all }}</ref> These hot deserts form the ''Global Sun Belt'' circling the world. This belt consists of extensive swathes of land in Northern Africa, [[Place:Southern Africa|Southern Africa]], Southwest Asia, [[Place:Middle East|Middle East]], and {{wipe|Australia}}, as well as the much smaller deserts of [[Earth:North America|North]] and [[Earth:South America|South America]].<ref>{{cite web |url=http://solarone.me/2016/07/27/living-in-the-sun-belt-the-solar-power-potential-for-the-middle-east/ |title=Living in the Sun Belt : The Solar Power Potential for the Middle East |date=27 July 2016 |access-date=2017-08-22 |url-status=live |archive-url=https://web.archive.org/web/20170826121314/http://solarone.me/2016/07/27/living-in-the-sun-belt-the-solar-power-potential-for-the-middle-east/ |archive-date=26 August 2017 |df=dmy-all }}</ref>

So solar is (or is predicted to become) the cheapest source of energy in all of Central America, Africa, the Middle East, India, South-east Asia, Australia, and several other places.<ref name="ReferenceA"/>{{Rp|page=8}}

Different measurements of [[Astronomy:Solar irradiance|solar irradiance]] (direct normal irradiance, global horizontal irradiance) are mapped below:

<gallery mode="packed" heights="150px">
File:SolarGIS-Solar-map-North-America-en.png|North America
File:SolarGIS-Solar-map-Latin-America-en.png|South America
File:SolarGIS-Solar-map-Europe-en.png|Europe
File:SolarGIS-Solar-map-Africa-and-Middle-East-en.png|Africa and Middle East
File:SolarGIS-Solar-map-South-And-South-East-Asia-en.png|South and South-East Asia
File:SolarGIS-Solar-map-Australia-en.png|Australia
File:SolarGIS-Solar-map-World-map-en.png|World
</gallery>

=== Self-consumption ===

In cases of self-consumption of solar energy, the payback time is calculated based on how much electricity is not purchased from the grid.<ref>{{cite web|url=https://docs.google.com/spreadsheet/pub?key=0Ahl2afL-jL0BdEVGU3dsbllfTzlxMEV0aTNqT0d5Nnc&output=html |title=Money saved by producing electricity from PV and Years for payback|url-status=live|archive-url= https://web.archive.org/web/20141228114744/https://docs.google.com/spreadsheet/pub?key=0Ahl2afL-jL0BdEVGU3dsbllfTzlxMEV0aTNqT0d5Nnc&output=html |archive-date=28 December 2014|df=dmy-all}}</ref> However, in many cases, the patterns of generation and consumption do not coincide, and some or all of the energy is fed back into the grid. The electricity is sold, and at other times when energy is taken from the grid, electricity is bought. The relative costs and prices obtained affect the economics. In many markets, the price paid for sold PV electricity is significantly lower than the price of bought electricity, which incentivizes self-consumption.<ref name="iea-pvps-trends-2014">{{cite report |title=Trends in Photovoltaic Applications 2014 |publisher=IEA-PVPS |date=2014 |url=http://iea-pvps.org/fileadmin/dam/public/report/statistics/IEA_PVPS_Trends_2014_in_PV_Applications_-_lr.pdf |url-status=live |archive-url=https://web.archive.org/web/20170525165925/http://iea-pvps.org/fileadmin/dam/public/report/statistics/IEA_PVPS_Trends_2014_in_PV_Applications_-_lr.pdf |archive-date=25 May 2017 |df=dmy-all }}</ref> Moreover, separate self-consumption incentives have been used in e.g., Germany and Italy.<ref name="iea-pvps-trends-2014"/> Grid interaction regulation has also included limitations of grid feed-in in some regions in Germany with high amounts of installed PV capacity.<ref name="iea-pvps-trends-2014"/><ref>{{cite journal |last1=Stetz |first1=T |last2=Marten |first2=F |last3=Braun |first3=M |title=Improved Low Voltage Grid-Integration of Photovoltaic Systems in Germany |journal=IEEE Transactions on Sustainable Energy |date=2013 |volume=4 |issue=2 |pages=534–542 |doi=10.1109/TSTE.2012.2198925|bibcode=2013ITSE....4..534S |s2cid=47032066 }}</ref> By increasing self-consumption, the grid feed-in can be limited without [[Engineering:Curtailment (electricity)|curtailment]], which wastes electricity.<ref name="salpakari-lund-2016">{{cite journal |last1=Salpakari |first1=Jyri |last2=Lund |first2=Peter |title=Optimal and rule-based control strategies for energy flexibility in buildings with PV |journal=Applied Energy |date=2016 |volume=161 |pages=425–436 |doi=10.1016/j.apenergy.2015.10.036|bibcode=2016ApEn..161..425S |s2cid=59037572 |url=https://aaltodoc.aalto.fi/handle/123456789/25788 }}</ref>

A good match between generation and consumption is key for high self-consumption. The match can be improved with batteries or controllable electricity consumption.<ref name="salpakari-lund-2016"/> However, batteries are expensive, and profitability may require the provision of other services from them besides self-consumption increase,<ref name="rmi-battery-2015">{{cite report |last1=Fitzgerald |first1=Garrett |last2=Mandel |first2=James |last3=Morris |first3=Jesse |last4=Touati |first4=Hervé |title=The Economics of Battery Energy Storage |publisher=Rocky Mountain Institute |date=2015 |url=http://www.rmi.org/Content/Files/RMI-TheEconomicsOfBatteryEnergyStorage-FullReport-FINAL.pdf |url-status=dead |archive-url=https://web.archive.org/web/20161130145345/http://www.rmi.org/Content/Files/RMI-TheEconomicsOfBatteryEnergyStorage-FullReport-FINAL.pdf |archive-date=30 November 2016 |df=dmy-all }}</ref> for example avoiding [[Engineering:Power outage|power outage]]s.<ref>{{Cite web |title=The Value of Electricity Reliability: Evidence from Battery Adoption |url=https://www.rff.org/publications/working-papers/the-value-of-electricity-reliability-evidence-from-battery-adoption/ |access-date=2023-06-14 |website=Resources for the Future |language=en-US}}</ref> [[Physics:Hot water storage tank|Hot water storage tank]]s with electric heating with heat pumps or resistance heaters can provide low-cost storage for self-consumption of solar power.<ref name="salpakari-lund-2016"/> Shiftable loads, such as dishwashers, tumble dryers and washing machines, can provide controllable consumption with only a limited effect on the users, but their effect on self-consumption of solar power may be limited.<ref name="salpakari-lund-2016"/>

=== Energy pricing, incentives and taxes ===

The original political purpose of incentive policies for PV was to facilitate an initial small-scale deployment to begin to grow the industry, even where the cost of PV was significantly above grid parity, to allow the industry to achieve the economies of scale necessary to reach grid parity. Since reaching grid parity some policies are implemented to promote national energy independence,<ref name=":6">{{Cite web |date=2022-04-06 |title=Germany boosts renewables with "biggest energy policy reform in decades" |url=https://www.cleanenergywire.org/news/germany-boosts-renewables-biggest-energy-policy-reform-decades |access-date=2022-11-08 |website=Clean Energy Wire |language=en}}</ref> high tech job creation<ref>{{Cite web |title=Indigenizing Solar Manufacturing: Charting the Course to a Solar Self-Sufficient India - Saur Energy International |url=https://www.saurenergy.com/solar-energy-articles/indigenizing-solar-manufacturing-charting-the-course-to-a-solar-self-sufficient-india |access-date=2022-11-08 |website=www.saurenergy.com}}</ref> and reduction of CO<sub>2</sub> emissions.<ref name=":6" />

Financial incentives for photovoltaics differ across countries, including [[Engineering:Solar power in Australia|Australia]],<ref>{{Cite web |title=Renewable power incentives |url=https://www.energy.gov.au/rebates/renewable-power-incentives}}</ref> China,<ref>[https://www.cnbc.com/id/32551044/site/14081545 China Racing Ahead of America in the Drive to Go Solar]. {{webarchive|url=https://web.archive.org/web/20130706133417/http://www.cnbc.com/id/32551044/site/14081545|date=6 July 2013}}</ref> Germany,<ref name="German PV market">{{cite web |title=Power & Energy Technology - IHS Technology |url=http://www.solarbuzz.com/FastFactsGermany.htm |url-status=live |archive-url=https://web.archive.org/web/20100102171748/http://solarbuzz.com/FastFactsGermany.htm |archive-date=2 January 2010 |df=dmy-all}}</ref> India,<ref>{{Cite web |author=Ravi Shankar|date=Jul 20, 2022 |title=What is the solar rooftop subsidy scheme/yojana? - Times of India |url=https://timesofindia.indiatimes.com/business/faqs/miscellaneous/what-is-the-solar-rooftop-subsidy-scheme/yojana/articleshow/93010587.cms |access-date=2022-11-08 |website=The Times of India |language=en}}</ref> Japan, and the United States and even across states within the US.

==== Net metering ====
[[File:Feed-in Tariff meter connections.png|thumb|upright=1.5|Net metering, unlike a feed-in tariff, requires only one meter, but it must be bi-directional.]]

In [[Finance:Net metering|net metering]] the price of the electricity produced is the same as the price supplied to the consumer, and the consumer is billed on the difference between production and consumption. Net metering can usually be done with no changes to standard [[Physics:Electricity meter|electricity meter]]s, which accurately measure power in both directions and automatically report the difference, and because it allows homeowners and businesses to generate electricity at a different time from consumption, effectively using the grid as a giant storage battery. With net metering, deficits are billed each month while surpluses are rolled over to the following month. Best practices call for perpetual roll over of kWh credits.<ref>{{cite web|url=http://www.dsireusa.org/solar/solarpolicyguide/?id=17|archive-url=https://web.archive.org/web/20121021172839/http://www.dsireusa.org/solar/solarpolicyguide/?id=17|url-status=dead|title=Net Metering|archive-date=21 October 2012}}</ref> Excess credits upon termination of service are either lost or paid for at a rate ranging from wholesale to retail rate or above, as can be excess annual credits.<ref>{{cite web|url=http://www.njcleanenergy.com/renewable-energy/programs/net-metering-and-interconnection|title=Net Metering and Interconnection - NJ OCE Web Site|url-status=live|archive-url=https://web.archive.org/web/20120512060609/http://www.njcleanenergy.com/renewable-energy/programs/net-metering-and-interconnection|archive-date=12 May 2012|df=dmy-all}}</ref>

====Community solar====
[[File:Solar farm in Wisconsin 01.jpg|thumb|Community solar farm in the town of Wheatland, Wisconsin<ref>{{Cite web |last=Mentzel |first=Dashal |date=2023-10-25 |title=Partnership brings benefits of community solar to Vernon County |url=https://www.weau.com/2023/10/25/partnership-brings-benefits-community-solar-vernon-county/ |access-date=2023-11-22 |website=WEAU |language=en}}</ref>]]
A community solar project is a solar power installation that accepts capital from and provides output credit and tax benefits to multiple customers, including individuals, businesses, nonprofits, and other investors. Participants typically invest in or subscribe to a certain kW capacity or kWh generation of remote electrical production.<ref>{{Cite web|title=Community Solar Basics |url=https://www.energy.gov/eere/solar/community-solar-basics |access-date=2021-09-17 |website=Energy.gov |language=en}}</ref>

==== Taxes ====
In some countries [[Finance:Tariff|tariffs (import taxes)]] are imposed on imported solar panels.<ref>{{Cite web |last=Philipp |first=Jennifer |date=2022-09-07 |title=Solar Power in Africa on the Rise |url=https://www.borgenmagazine.com/solar-power-in-africa/ |access-date=2022-09-15 |website=BORGEN |language=en-US}}</ref><ref>{{Cite web |last=Busch |first=Marc L. |date=2022-09-02 |title=The mystery of India's new solar tariffs |url=https://thehill.com/opinion/international/3625976-the-mystery-of-indias-new-solar-tariffs/ |access-date=2022-09-15 |website=The Hill |language=en-US}}</ref>

== Grid integration ==
{{main|Engineering:Energy storage|Engineering:Grid energy storage}}
[[File:Abengoa Solar (7336087392).jpg|thumb| Construction of the Salt Tanks which provide efficient [[Physics:Thermal energy storage|thermal energy storage]]<ref>Wright, matthew; Hearps, Patrick; et al. [http://media.bze.org.au/ZCA2020_Stationary_Energy_Report_v1.pdf Australian Sustainable Energy: Zero Carbon Australia Stationary Energy Plan] {{webarchive|url=https://web.archive.org/web/20151124173114/http://media.bze.org.au/ZCA2020_Stationary_Energy_Report_v1.pdf |date=24 November 2015 }}, Energy Research Institute, University of Melbourne, October 2010, p. 33. Retrieved from BeyondZeroEmissions.org website.</ref> so that output can be provided after sunset, and output can be scheduled to meet demand requirements.<ref>{{cite journal |last = Palgrave |first = Robert |date = 1 December 2008 |title = Innovation in CSP |url = http://www.renewableenergyfocus.com/view/3272/innovation-in-concentrating-thermal-solar-power-csp/ |url-status = dead |archive-url = https://web.archive.org/web/20150924090041/http://www.renewableenergyfocus.com/view/3272/innovation-in-concentrating-thermal-solar-power-csp/ |archive-date = 24 September 2015 |journal = Renewable Energy Focus |volume = 9 |issue = 6 |pages = 44–49 |publisher = Elsevier |doi = 10.1016/S1755-0084(08)70066-8}}</ref> The 280 MW Solana Generating Station is designed to provide six hours of energy storage. This allows the plant to generate about 38% of its rated capacity over the course of a year.<ref>{{cite web|url=http://blogs.phoenixnewtimes.com/valleyfever/2013/10/solana_10_facts_you_didnt_know.php|title=Solana: 10 Facts You Didn't Know About the Concentrated Solar Power Plant Near Gila Bend|author=Ray Stern|work=Phoenix New Times|url-status=live|archive-url=https://web.archive.org/web/20131011235507/http://blogs.phoenixnewtimes.com/valleyfever/2013/10/solana_10_facts_you_didnt_know.php|archive-date=11 October 2013|df=dmy-all|date=10 October 2013}}</ref>]]
{{multiple image
 |direction=vertical
 |align=right
 |width=225
 |image1=Andasol 3.jpg
 |image2=Geesthacht Energiepark.jpg
 |caption1=[[Physics:Thermal energy storage|Thermal energy storage]]. The Andasol CSP plant uses tanks of molten salt to store solar energy.
 |caption2=[[Engineering:Pumped-storage hydroelectricity|Pumped-storage hydroelectricity]] (PSH). This facility in Geesthacht, Germany, also includes a solar array.
}}

===Variability===
The overwhelming majority of electricity produced worldwide is used immediately because traditional generators can adapt to demand and storage is usually more expensive. Both solar power and wind power are [[Engineering:Variable renewable energy|sources of variable renewable power]], meaning that all available output must be used locally, carried on [[Finance:Electric power transmission|transmission]] lines to be used elsewhere, or stored (e.g., in a battery). Since solar energy is not available at night, storing it so as to have continuous electricity availability is potentially an important issue, particularly in off-grid applications and for future [[100% renewable energy|100% renewable energy]] scenarios.<ref>Carr (1976), p. 85</ref>

Solar electricity is inherently variable but somewhat predictable by time of day, location, and seasons (see [[Earth:Solar power forecasting|solar power forecasting]]). Solar is intermittent due to the day/night cycles and variable weather conditions. The challenge of integrating solar power in any given electric utility varies significantly. In places with hot summers and mild winters, solar is well matched to daytime cooling demands.<ref>{{Cite journal |last1=Ruggles |first1=Tyler H. |last2=Caldeira |first2=Ken |date=2022-01-01 |title=Wind and solar generation may reduce the inter-annual variability of peak residual load in certain electricity systems |journal=Applied Energy |language=en |volume=305 |pages=117773 |doi=10.1016/j.apenergy.2021.117773 |bibcode=2022ApEn..30517773R |s2cid=239113921 |issn=0306-2619|doi-access=free }}</ref>

=== Energy storage ===
[[Engineering:Concentrated solar power|Concentrated solar power]] plants may use [[Physics:Thermal energy storage|thermal storage]] to store solar energy, such as in high-temperature molten salts. These 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. This method of energy storage is used, for example, by the Solar Two power station, allowing it to store 1.44&nbsp;TJ in its 68&nbsp;m<sup>3</sup> storage tank, enough to provide full output for close to 39 hours, with an 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 |url-status = live |archive-url = https://web.archive.org/web/20110605094349/http://www.sandia.gov/Renewable_Energy/solarthermal/NSTTF/salt.htm |archive-date = 5 June 2011 |df = dmy-all}}</ref>

In [[Physics:Photovoltaic system#Standalone system|stand alone PV systems]] batteries are traditionally used to store excess electricity. With grid-connected photovoltaic power systems, excess electricity can be sent to the [[Engineering:Electrical grid|electrical grid]]. [[Finance:Net metering|Net metering]] and feed-in tariff programs give these systems a credit for the electricity they produce. This credit offsets electricity provided from the grid when the system cannot meet demand, effectively trading with the grid instead of storing excess electricity.<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}}</ref> 
When wind and solar are a small fraction of the grid power, other generation techniques can adjust their output appropriately, but as these forms of variable power grow, additional balance on the grid is needed. As prices are rapidly declining, PV systems increasingly use rechargeable batteries to store a surplus to be used later at night. Batteries used for grid-storage can stabilize the [[Engineering:Electrical grid|electrical grid]] by [[Engineering:Grid energy storage#Load leveling|leveling out peak loads]] for a few hours. In the future, less expensive batteries could play an important role on the electrical grid, as they can charge during periods when generation exceeds demand and feed their stored energy into the grid when demand is higher than generation.

Common battery technologies used in today's home PV systems include nickel-cadmium, lead-acid, nickel metal hydride, and [[Engineering:Lithium-ion battery|lithium-ion]].<ref name="MohantyMuneerKolhe2015">{{cite book | author1 = Parimita Mohanty | author2 = Tariq Muneer | author3 = Mohan Kolhe | date = 30 October 2015 | title = Solar Photovoltaic System Applications: A Guidebook for Off-Grid Electrification | publisher = Springer | isbn = 978-3-319-14663-8 | url = https://books.google.com/books?id=37zYCgAAQBAJ|access-date=22 August 2022|page=91}}</ref><ref name="Xiao2017">{{cite book | author = Weidong Xiao | date = 24 July 2017 | title = Photovoltaic Power System: Modeling, Design, and Control | publisher = John Wiley & Sons | page = 288| isbn = 978-1-119-28034-7 | url = https://books.google.com/books?id=DEHCDgAAQBAJ|access-date=22 August 2022}}</ref>{{Better source needed|reason=The current source is too old. All those battery types still common with solar?|date=November 2022}}Lithium-ion batteries have the potential to replace lead-acid batteries in the near future, as they are being intensively developed and lower prices are expected due to [[Finance:Economies of scale|economies of scale]] provided by large production facilities such as the Gigafactory 1. In addition, the Li-ion batteries of plug-in [[Engineering:Electric car|electric car]]s may serve as future storage devices in a [[Engineering:Vehicle-to-grid|vehicle-to-grid]] system. Since most vehicles are parked an average of 95% of the time, their batteries could be used to let electricity flow from the car to the power lines and back. Other rechargeable batteries used for distributed PV systems include, [[Engineering:Sodium–sulfur battery|sodium–sulfur]] and [[Chemistry:Vanadium redox battery|vanadium redox]] batteries, two prominent types of a molten salt and a [[Chemistry:Flow battery|flow]] battery, respectively.<ref name=ethz-Harvard>{{cite web |publisher=ETH Zürich, Harvard University |url=https://www.researchgate.net/publication/264239770 |title=The Economic Viability of Battery Storage for Residential Solar Photovoltaic Systems - A Review and a Simulation Model |author1=Joern Hoppmann |author2=Jonas Volland |author3=Tobias S. Schmidt |author4=Volker H. Hoffmann |date=July 2014 |url-status=live |archive-url=https://web.archive.org/web/20150403122002/http://www.researchgate.net/publication/264239770_The_Economic_Viability_of_Battery_Storage_for_Residential_Solar_Photovoltaic_Systems_-_A_Review_and_a_Simulation_Model |archive-date=3 April 2015 |df=dmy-all }}</ref><ref>{{Cite web|last=Gerdes|first=Justin|title=Solar Energy Storage About To Take Off In Germany and California|url=https://www.forbes.com/sites/justingerdes/2013/07/18/solar-energy-storage-about-to-take-off-in-germany-and-california/|url-status=live|archive-url=https://web.archive.org/web/20170729205924/https://www.forbes.com/sites/justingerdes/2013/07/18/solar-energy-storage-about-to-take-off-in-germany-and-california/|archive-date=2017-07-29|access-date=2023-02-08|work={{wipe|Forbes}}|language=en}}</ref><ref>{{cite news |agency=Associated Press |url=http://www.cbc.ca/news/business/tesla-launches-powerwall-home-battery-with-aim-to-revolutionize-energy-consumption-1.3056587 |title=Tesla launches Powerwall home battery with aim to revolutionize energy consumption |date=1 May 2015 |url-status=live |archive-url=https://web.archive.org/web/20150607013500/http://www.cbc.ca/news/business/tesla-launches-powerwall-home-battery-with-aim-to-revolutionize-energy-consumption-1.3056587 |archive-date=7 June 2015 |df=dmy-all }}</ref>

[[File:Seasonal cycle of capacity factors for wind and photovoltaics in Europe under idealized assumptions.png|thumb|Seasonal cycle of capacity factors for wind and photovoltaics in Europe under idealized assumptions. The figure illustrates the balancing effects of wind and solar energy at the seasonal scale (Kaspar et al., 2019).<ref name="balancing-europe">{{Cite journal|last1=Kaspar|first1=Frank|last2=Borsche|first2=Michael|last3=Pfeifroth|first3=Uwe|last4=Trentmann|first4=Jörg|last5=Drücke|first5=Jaqueline|last6=Becker|first6=Paul|date=2019-07-02|title=A climatological assessment of balancing effects and shortfall risks of photovoltaics and wind energy in Germany and Europe|url=https://asr.copernicus.org/articles/16/119/2019/|url-status=live|archive-url=https://web.archive.org/web/20211124094345/https://asr.copernicus.org/articles/16/119/2019/|archive-date=2021-11-24|journal=Advances in Science and Research|language=English|publisher=Copernicus GmbH|volume=16|pages=119–128|doi=10.5194/asr-16-119-2019|doi-access=free|bibcode=2019AdSR...16..119K |s2cid=198316727 }}</ref>]]

=== Other technologies ===
Solar power plants, while they can be curtailed, usually simply output as much power as possible. Therefore in an electricity system without sufficient [[Engineering:Grid energy storage|grid energy storage]], generation from other sources (coal, biomass, natural gas, nuclear, hydroelectricity) generally go up and down in reaction to the rise and fall of solar electricity and variations in demand (see [[Engineering:Load following power plant|load following power plant]]). 

Conventional hydroelectric dams work very well in conjunction with solar power; water can be held back or released from a reservoir as required. Where suitable geography is not available, [[Engineering:Pumped-storage hydroelectricity|pumped-storage hydroelectricity]] can use solar power to pump water to a high reservoir on sunny days, then the energy is recovered at night and in bad weather by releasing water via a hydroelectric plant to a low reservoir where the cycle can begin again.<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  |url-status=dead  |archive-url=https://web.archive.org/web/20080621052054/http://www.electricitystorage.org/tech/technologies_technologies_pumpedhydro.htm  |archive-date=21 June 2008  |df=dmy }}</ref>

While hydroelectric and natural gas plants can quickly respond to changes in load; coal, biomass and nuclear plants usually take considerable time to respond to load and can only be scheduled to follow the predictable variation. Depending on local circumstances, beyond about 20–40% of total generation, grid-connected [[Engineering:Intermittent energy source|intermittent source]]s like solar tend to require investment in some combination of grid interconnections, [[Engineering:Grid energy storage|energy storage]] or demand side management. In countries with high solar generation, such as Australia, electricity prices may become negative in the middle of the day when solar generation is high, thus incentivizing new [[Physics:Battery storage power station|battery storage]].<ref>{{Cite web |last=Parkinson |first=Giles |date=2022-10-23 |title="We don't need solar technology breakthroughs, we just need connections" |url=https://reneweconomy.com.au/we-dont-need-solar-technology-breakthroughs-we-just-need-connections/ |access-date=2022-11-08 |website=RenewEconomy |language=en-AU}}</ref><ref>{{Cite web |last=Vorrath |first=Sophie |date=2022-10-17 |title=MPower gets green light to connect solar battery projects, cash in on negative pricing |url=https://reneweconomy.com.au/mpower-gets-green-light-to-connect-solar-and-battery-projects-cash-in-on-negative-pricing/ |access-date=2022-11-08 |website=RenewEconomy |language=en-AU}}</ref>

The combination of wind and solar PV has the advantage that the two sources complement each other because the peak operating times for each system occur at different times of the day and year.<ref>{{Cite journal |last1=Nyenah |first1=Emmanuel |last2=Sterl |first2=Sebastian |last3=Thiery |first3=Wim |date=2022-05-01 |title=Pieces of a puzzle: solar-wind power synergies on seasonal and diurnal timescales tend to be excellent worldwide |journal=Environmental Research Communications |language=en |volume=4 |issue=5 |pages=055011 |doi=10.1088/2515-7620/ac71fb |bibcode=2022ERCom...4e5011N |s2cid=249227821 |issn=2515-7620|doi-access=free }}</ref> The power generation of such [[Engineering:Solar hybrid power systems|solar hybrid power systems]] is therefore more constant and fluctuates less than each of the two component subsystems.<ref name="auto">{{cite web |date=2 July 2012 |title=Hybrid Wind and Solar Electric Systems |url=http://energy.gov/energysaver/articles/hybrid-wind-and-solar-electric-systems |url-status=live |archive-url=https://web.archive.org/web/20150526061658/http://energy.gov/energysaver/articles/hybrid-wind-and-solar-electric-systems |archive-date=26 May 2015 |publisher=United States Department of Energy |df=dmy-all}}</ref> Solar power is seasonal, particularly in northern/southern climates, away from the equator, suggesting a need for long term seasonal storage in a medium such as hydrogen or pumped hydroelectric.<ref>{{cite journal|url=https://pdfs.semanticscholar.org/aee9/8815cc874423e67af5fd9bf8eac612b56ea6.pdf|title=Seasonal Energy Storage in a Renewable Energy System|journal=Proceedings of the IEEE|year=2012|doi=10.1109/JPROC.2011.2105231|s2cid=9195655|access-date=30 April 2018|url-status=dead|archive-url=https://web.archive.org/web/20161108150209/https://pdfs.semanticscholar.org/aee9/8815cc874423e67af5fd9bf8eac612b56ea6.pdf|archive-date=8 November 2016|df=dmy-all|last1=Converse|first1=Alvin O.|volume=100|issue=2|pages=401–409}}</ref>

== Environmental effects ==
[[File:Greenhouse gas emissions per energy source.png|thumb|Greenhouse gas emissions per energy source. Solar power is one of the sources with the least greenhouse gas emissions.]]

[[File:Blick vom aussichtsturm hörlitz4.jpg|thumb|Part of the Senftenberg Solarpark, a solar photovoltaic power plant located on former open-pit mining areas close to the city of Senftenberg, in Eastern Germany. The 78 MW Phase 1 of the plant was completed within three months.]]

Solar power is cleaner than electricity from fossil fuels,<ref name=":5" /> so can be good for the environment when it replaces that.<ref>{{Cite web |title=Solar energy and the environment - U.S. Energy Information Administration (EIA) |url=https://www.eia.gov/energyexplained/solar/solar-energy-and-the-environment.php#:~:text=Solar%20energy%20technologies%20and%20power,larger%20effects%20on%20the%20environment. |access-date=2023-05-31 |website=www.eia.gov}}</ref> Solar power does not lead to any harmful emissions during operation, but the production of the panels leads to some amount of pollution. A 2021 study estimated the carbon footprint of manufacturing monocrystalline panels at 515 g {{CO2}}/kWp in the US and 740 g {{CO2}}/kWp in China,<ref>{{Cite book |last=Anctil |first=Annick |title=2021 IEEE 48th Photovoltaic Specialists Conference (PVSC) |chapter=Comparing the carbon footprint of monocrystalline silicon solar modules manufactured in China and the United States |date=June 2021 |chapter-url=https://ieeexplore.ieee.org/document/9518632 |pages=1–3 |doi=10.1109/PVSC43889.2021.9518632|isbn=978-1-6654-1922-2 |s2cid=237332457 }}</ref> but this is expected to fall as manufacturers use more clean electricity and recycled materials.<ref name=":3">{{Cite web |date=2022-09-21 |title=Solar power's potential limited unless "you do everything perfectly" says solar scientist |url=https://www.dezeen.com/2022/09/21/wim-c-sinke-interview-solar-power-limitations/ |access-date=2022-10-15 |website=Dezeen |language=en}}</ref> Solar power carries an upfront cost to the environment via production with a carbon payback time of several years {{As of|2022|lc=y}},<ref name=":3" /> but offers clean energy for the remainder of their 30-year lifetime.<ref>{{Cite web |title=Aging Gracefully: How NREL Is Extending the Lifetime of Solar Modules |url=https://www.nrel.gov/news/features/2022/aging-gracefully-how-nrel-is-extending-the-lifetime-of-solar-modules.html |access-date=2022-10-15 |website=www.nrel.gov |language=en}}</ref>

The [[Physics:Life-cycle greenhouse-gas emissions of energy sources|life-cycle greenhouse-gas emissions of solar farms]] are less than 50&nbsp;gram (g) per [[Kilowatt-hour|kilowatt-hour]] (kWh),<ref>{{Cite journal |last1=Zhu |first1=Xiaonan |last2=Wang |first2=Shurong |last3=Wang |first3=Lei |date=April 2022 |title=Life cycle analysis of greenhouse gas emissions of China's power generation on spatial and temporal scale |journal=Energy Science & Engineering |language=en |volume=10 |issue=4 |pages=1083–1095 |doi=10.1002/ese3.1100 |bibcode=2022EneSE..10.1083Z |s2cid=247443046 |issn=2050-0505|doi-access=free }}</ref><ref>{{Cite web |title=Carbon Neutrality in the UNECE Region: Integrated Life-cycle Assessment of Electricity Sources |url=https://unece.org/sites/default/files/2022-04/LCA_3_FINAL%20March%202022.pdf |page=49}}</ref><ref name=":0">{{Cite web |title=Life Cycle Greenhouse Gas Emissions from Solar Photovoltaics |url=https://www.nrel.gov/docs/fy13osti/56487.pdf}}</ref> but with battery storage could be up to 150 g/kWh.<ref>{{Cite journal |last1=Mehedi |first1=Tanveer Hassan |last2=Gemechu |first2=Eskinder |last3=Kumar |first3=Amit |date=2022-05-15 |title=Life cycle greenhouse gas emissions and energy footprints of utility-scale solar energy systems |url=https://www.sciencedirect.com/science/article/pii/S0306261922003403 |journal=Applied Energy |language=en |volume=314 |pages=118918 |doi=10.1016/j.apenergy.2022.118918 |bibcode=2022ApEn..31418918M |s2cid=247726728 |issn=0306-2619}}</ref> In contrast, a [[Physics:Combined cycle|combined cycle]] gas-fired power plant without [[Physics:Carbon capture and storage|carbon capture and storage]] emits around 500&nbsp;g/kWh, and a coal-fired power plant about 1000&nbsp;g/kWh.<ref>{{Cite web|title=Life Cycle Assessment Harmonization|url=https://www.nrel.gov/analysis/life-cycle-assessment.html|access-date=2021-12-04|website=www.nrel.gov|language=en}}</ref> Similar to all energy sources where their total life cycle emissions are mostly from construction, the switch to low carbon power in the manufacturing and transportation of solar devices would further reduce carbon emissions.<ref name=":0" />

Lifecycle [[Physics:Surface power density|surface power density]] of solar power varies a lot<ref name=":1" /> but averages about 7 W/m2, compared to about 240 for [[Physics:Nuclear power|nuclear power]] and 480 for gas.<ref>{{Cite journal |date=2018-12-01 |title=The spatial extent of renewable and non-renewable power generation: A review and meta-analysis of power densities and their application in the U.S. |journal=Energy Policy |language=en |volume=123 |pages=83–91 |doi=10.1016/j.enpol.2018.08.023 |issn=0301-4215 |doi-access=free |last1=Van Zalk |first1=John |last2=Behrens |first2=Paul |hdl=1887/64883 |hdl-access=free}}</ref> However when the land required for gas extraction and processing is accounted for gas power is estimated to have not much higher power density than solar.<ref name=":5" /> PV requires much larger amounts of land surface to produce the same nominal amount of energy as sources{{Which|date=May 2023}} with higher surface power density and capacity factor. According to a 2021 study, obtaining 25 to 80% of electricity from solar farms in their own territory by 2050 would require the panels to cover land ranging from 0.5 to 2.8% of the European Union, 0.3 to 1.4% in India, and 1.2 to 5.2% in Japan and South Korea.<ref>{{Cite journal |last1=van de Ven |first1=Dirk-Jan |last2=Capellan-Peréz |first2=Iñigo |last3=Arto |first3=Iñaki |last4=Cazcarro |first4=Ignacio |last5=de Castro |first5=Carlos |last6=Patel |first6=Pralit |last7=Gonzalez-Eguino |first7=Mikel |date=2021-02-03 |title=The potential land requirements and related land use change emissions of solar energy |journal=Scientific Reports |language=en |volume=11 |issue=1 |pages=2907 |issn=2045-2322 |doi=10.1038/s41598-021-82042-5 |pmid=33536519 |pmc=7859221 |bibcode=2021NatSR..11.2907V}}</ref> Occupation of such large areas for PV farms could drive residential opposition as well as lead to deforestation, removal of vegetation and conversion of farm land.<ref>{{cite web |last=Diab |first=Khaled |title=There are grounds for concern about solar power |url=https://www.aljazeera.com/opinions/2021/4/7/there-are-grounds-for-concern-about-solar-power |access-date=2021-04-15 |website=www.aljazeera.com |language=en}}</ref> However some countries, such as South Korea and Japan, use land for agriculture under PV,<ref>{{Cite web |last=Staff |first=Carbon Brief |date=2022-08-25 |title=Factcheck: Is solar power a 'threat' to UK farmland? |url=https://www.carbonbrief.org/factcheck-is-solar-power-a-threat-to-uk-farmland/ |access-date=2022-09-15 |website=Carbon Brief |language=en}}</ref><ref>{{Cite web |last=Oda |first=Shoko |date=2022-05-21 |title=Electric farms in Japan are using solar power to grow profits and crops |url=https://www.japantimes.co.jp/news/2022/05/21/business/electric-farms-japan-solar/ |access-date=2022-10-14 |website=The Japan Times |language=en-US}}</ref> or floating solar,<ref>{{Cite web |last=Gerretsen |first=Isabelle |title=The floating solar panels that track the Sun |url=https://www.bbc.com/future/article/20221116-the-floating-solar-panels-that-track-the-sun |access-date=2022-11-29 |website=www.bbc.com |language=en}}</ref> together with other low-carbon power sources.<ref>{{Cite web |last=Pollard |first=Jim |date=2023-05-29 |title=Wind Power Body Plans to Provide a Third of Japan's Electricity |url=https://www.asiafinancial.com/wind-power-body-plans-to-provide-a-third-of-japans-electricity |access-date=2023-05-31 |website=Asia Financial |language=en-US}}</ref><ref>{{Cite web |title=Clean power in South Korea |url=https://climateanalytics.org/media/clean_power_in_south_korea.pdf}}</ref> Worldwide land use has minimal ecological impact.<ref>{{Cite journal |last1=Dunnett |first1=Sebastian |last2=Holland |first2=Robert A. |last3=Taylor |first3=Gail |last4=Eigenbrod |first4=Felix |date=2022-02-08 |title=Predicted wind and solar energy expansion has minimal overlap with multiple conservation priorities across global regions |journal=Proceedings of the National Academy of Sciences |language=en |volume=119 |issue=6 |doi=10.1073/pnas.2104764119 |issn=0027-8424 |pmid=35101973 |pmc=8832964 |bibcode=2022PNAS..11904764D}}</ref> Land use can be reduced to the level of gas power by installing on buildings and other built up areas.<ref name=":1">{{Cite web |title=How does the land use of different electricity sources compare? |url=https://ourworldindata.org/land-use-per-energy-source |access-date=2022-11-03 |website=Our World in Data}}</ref>

Harmful materials are used in the production of solar panels, but in generally in small amounts.<ref>{{Cite journal |last1=Rabaia |first1=Malek Kamal Hussien |last2=Abdelkareem |first2=Mohammad Ali |last3=Sayed |first3=Enas Taha |last4=Elsaid |first4=Khaled |last5=Chae |first5=Kyu-Jung |last6=Wilberforce |first6=Tabbi |last7=Olabi |first7=A. G. |date=2021 |title=Environmental impacts of solar energy systems: A review |url=https://www.sciencedirect.com/science/article/pii/S0048969720355182 |journal=Science of the Total Environment |language=en |volume=754 |pages=141989 |doi=10.1016/j.scitotenv.2020.141989 |pmid=32920388 |bibcode=2021ScTEn.754n1989R |s2cid=221671774 |issn=0048-9697}}</ref>  {{As of|2022}} the environmental impact of perovskite is hard to estimate, but there is some concern that [[Chemistry:Lead|lead]] may become a problem.<ref name=":5">{{Cite journal |last=Urbina |first=Antonio |date=2022-10-26 |title=Sustainability of photovoltaic technologies in future net-zero emissions scenarios |journal=Progress in Photovoltaics: Research and Applications |volume=31 |issue=12 |language=en |pages=1255–1269 |doi=10.1002/pip.3642 |issn=1062-7995 |s2cid=253195560 |quote=the apparent contradiction that can arise from the fact that large PV plants occupy more land than the relatively compact coal or gas plants is due to the inclusion in the calculation of impacts in land occupation arising from coal mining and oil or gas extraction; if they are included, the impact on land occupation is larger for fossil fuels.|doi-access=free }}</ref> A 2021 [[Organization:International Energy Agency|International Energy Agency]] study projects the demand for [[Chemistry:Copper|copper]] will double by 2040. The study cautions that supply needs to increase rapidly to match demand from large-scale deployment of solar and required grid upgrades.<ref>{{Cite web|date=2021-05-05|title=Renewable revolution will drive demand for critical minerals|url=https://reneweconomy.com.au/renewable-revolution-will-drive-demand-for-critical-minerals/|access-date=2021-05-05|website=RenewEconomy|language=en-AU}}</ref><ref>{{Cite web|title=Clean energy demand for critical minerals set to soar as the world pursues net zero goals - News|url=https://www.iea.org/news/clean-energy-demand-for-critical-minerals-set-to-soar-as-the-world-pursues-net-zero-goals|access-date=2021-05-05|website=IEA|language=en-GB}}</ref> More [[Chemistry:Tellurium|tellurium]] and [[Chemistry:Indium|indium]] may also be needed and recycling may help.<ref name=":5" />

As solar panels are sometimes replaced with more efficient panels, the second-hand panels are sometimes reused in developing countries, for example in Africa.<ref>{{Cite news |title=Used Solar Panels Are Powering the Developing World |url=https://www.bloomberg.com/opinion/articles/2021-08-25/used-solar-panels-are-powering-the-developing-world |access-date=2022-09-15 |newspaper=Bloomberg.com|date=25 August 2021 }}</ref> Several countries have specific regulations for the recycling of solar panels.<ref>{{Cite web |last=US EPA |first=OLEM |date=2021-08-23 |title=End-of-Life Solar Panels: Regulations and Management |url=https://www.epa.gov/hw/end-life-solar-panels-regulations-and-management |access-date=2022-09-15 |website=www.epa.gov |language=en}}</ref><ref>{{Cite web |title=The Proposed Legal Framework On Responsibility Of Producers And... |url=https://www.roedl.com/insights/renewable-energy/2021/november/proposed-legal-framework-responsibility-producers-importers-solar-panels |access-date=2022-09-15 |website=www.roedl.com |language=en-us}}</ref><ref>{{Cite journal |last1=Majewski |first1=Peter |last2=Al-shammari |first2=Weam |last3=Dudley |first3=Michael |last4=Jit |first4=Joytishna |last5=Lee |first5=Sang-Heon |last6=Myoung-Kug |first6=Kim |last7=Sung-Jim |first7=Kim |date=2021-02-01 |title=Recycling of solar PV panels- product stewardship and regulatory approaches |url=https://www.sciencedirect.com/science/article/pii/S0301421520307734 |journal=Energy Policy |language=en |volume=149 |pages=112062 |doi=10.1016/j.enpol.2020.112062 |s2cid=230529644 |issn=0301-4215}}</ref> Although maintenance cost is already low compared to other energy sources,<ref>{{Cite journal |last=Gürtürk |first=Mert |date=2019-03-15 |title=Economic feasibility of solar power plants based on PV module with levelized cost analysis |url=https://www.sciencedirect.com/science/article/pii/S0360544219301008 |journal=Energy |language=en |volume=171 |pages=866–878 |doi=10.1016/j.energy.2019.01.090 |s2cid=116733543 |issn=0360-5442}}</ref> some academics have called for solar power systems to be designed to be more repairable.<ref>{{Cite journal |last1=Cross |first1=Jamie |last2=Murray |first2=Declan |date=2018-10-01 |title=The afterlives of solar power: Waste and repair off the grid in Kenya |journal=Energy Research & Social Science |language=en |volume=44 |pages=100–109 |doi=10.1016/j.erss.2018.04.034 |s2cid=53058260 |issn=2214-6296|doi-access=free }}</ref><ref>{{Cite book |last1=Jang |first1=Esther |last2=Barela |first2=Mary Claire |last3=Johnson |first3=Matt |last4=Martinez |first4=Philip |last5=Festin |first5=Cedric |last6=Lynn |first6=Margaret |last7=Dionisio |first7=Josephine |last8=Heimerl |first8=Kurtis |title=Proceedings of the 2018 CHI Conference on Human Factors in Computing Systems |chapter=Crowdsourcing Rural Network Maintenance and Repair via Network Messaging |date=2018-04-19 |chapter-url=https://doi.org/10.1145/3173574.3173641 |series=CHI '18 |location=New York, NY, US |publisher=Association for Computing Machinery |pages=1–12 |doi=10.1145/3173574.3173641 |isbn=978-1-4503-5620-6|s2cid=4950067 }}</ref>

A very small proportion of solar power is [[Engineering:Concentrated solar power|concentrated solar power]]. Concentrated solar power may use much more water than gas-fired power. This can be a problem, as this type of solar power needs strong sunlight so is often built in deserts.<ref>{{Cite web |title=Water consumption solution for efficient concentrated solar power {{!}} Research and Innovation |url=https://ec.europa.eu/research-and-innovation/en/projects/success-stories/all/water-consumption-solution-efficient-concentrated-solar-power |access-date=2021-12-04 |website=ec.europa.eu |language=en}}</ref>

== Politics ==
[[File:202307 Survey - comfortable with solar wind nuclear in my community.svg|thumb |Acceptance of wind and solar facilities in one's community is stronger among U.S. Democrats (blue), while acceptance of nuclear power plants is stronger among U.S. Republicans (red).<ref name=WashPost_20231003>{{cite news |last1=Chiu |first1=Allyson |last2=Guskin |first2=Emily |last3=Clement |first3=Scott |title=Americans don't hate living near solar and wind farms as much as you might think |url=https://www.washingtonpost.com/climate-solutions/2023/10/03/solar-panels-wind-turbines-nimby/ |newspaper=The Washington Post |date=3 October 2023 |archive-url=https://web.archive.org/web/20231003211732/https://www.washingtonpost.com/climate-solutions/2023/10/03/solar-panels-wind-turbines-nimby/ |archive-date=3 October 2023 | url-status=live }}</ref>]]
Solar production cannot be cut off by geopolitics once installed, unlike oil and gas, which contributes to energy security.<ref>{{Cite web |title=Making solar a source of EU energy security {{!}} Think Tank {{!}} European Parliament |url=https://www.europarl.europa.eu/thinktank/en/document/EPRS_ATA(2022)733587 |access-date=2022-11-03 |website=www.europarl.europa.eu |language=en}}</ref>

{{As of|2022}} over 40% of global polysilicon manufacturing capacity is in [[Place:Xinjiang|Xinjiang]] in {{wipe|China}},<ref>{{Cite news |last1=Blunt |first1=Katherine |last2=Dvorak |first2=Phred |date=2022-08-09 |title=WSJ News Exclusive {{!}} U.S. Solar Shipments Are Hit by Import Ban on China's Xinjiang Region |language=en-US |work={{wipe|The Wall Street Journal}} |url=https://www.wsj.com/articles/u-s-solar-shipments-are-hit-by-import-ban-on-chinas-xinjiang-region-11660037401 |access-date=2022-09-08 |issn=0099-9660}}</ref> which raises concerns about human rights violations ([[Religion:Xinjiang internment camps|Xinjiang internment camps]]) as well as supply chain dependency.<ref>{{cite web |date=2021-02-10 |title=Fears over China's Muslim forced labor loom over EU solar power |url=https://www.politico.eu/article/xinjiang-china-polysilicon-solar-energy-europe/ |access-date=2021-04-15 |website=Politico |language=en-US}}</ref>

==See also==
{{Div col|colwidth=22em}}<!---♦♦♦ Please keep the list in alphabetical order ♦♦♦--->
* [[100% renewable energy|100% renewable energy]]
* [[Finance:Cost of electricity by source|Cost of electricity by source]]
* [[Engineering:Gravity battery|Gravity battery]]
* Index of solar energy articles
* [[Earth:List of cities by sunshine duration|List of cities by sunshine duration]]
* List of photovoltaic power stations
* List of solar thermal power stations
* List of solar-powered products
* [[Social:Renewable energy commercialization|Renewable energy commercialization]]
* [[Physics:Solar energy|Solar energy]]
* [[Engineering:Solar lamp|Solar lamp]]
* [[Physics:Solar vehicle|Solar vehicle]]
* [[Earth:Sustainable energy|Sustainable energy]]
* [[Engineering:Thin-film solar cell|Thin-film solar cell]]
* [[Physics:Timeline of solar cells|Timeline of solar cells]]
{{Div col end}}
{{Clear}}

==References==
{{Reflist}}

== Bibliography ==
{{refbegin}}
* {{cite book|url={{google books |plainurl=y |id=xHFK9cM77a8C |p=50}}|title=From space to Earth: the story of solar electricity|last=Perlin|first=John|publisher=Earthscan|year=1999|isbn=978-0-937948-14-9|page=50}}
{{refend}}

== Further reading ==
{{Library resources box}}
*{{cite book
|last=Sivaram
|first=Varun
|title=Taming the Sun: Innovation to Harness Solar Energy and Power the Planet
|location=Cambridge, MA
|publisher=MIT Press
|year=2018
|isbn=978-0-262-03768-6}}

==External links==
* [https://www.eia.gov/energyexplained/solar/solar-energy-and-the-environment.php Solar energy and the environment] at U.S. Energy Information Administration


{{Electricity generation|state=autocollapse}}

{{DEFAULTSORT:Solar Power}}
[[Category:Energy conversion]]
[[Category:Sun|Power]]

{{Sourceattribution|Solar power|1}}