View source for Chemistry:Photovoltaics

{{short description|Method to produce electricity from solar radiation}}
[[File:SoSie+SoSchiff Ansicht.jpg|thumb|The Solar Settlement, a sustainable housing community project in Freiburg, Germany|upright=1.2]]
[[File:Ombrière SUDI - Sustainable Urban Design & Innovation.jpg|thumb|Charging station in France that provides energy for electric cars using solar energy|upright=1.2]]
[[File:ROSSA.jpg|thumb|Solar panels on the [[Astronomy:International Space Station|International Space Station]]|upright=1.2]]'''Photovoltaics''' ('''PV''') is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and [[Chemistry:Electrochemistry|electrochemistry]]. The photovoltaic effect is commercially used for electricity generation and as photosensors.

A [[Physics:Photovoltaic system|photovoltaic system]] employs solar modules, each comprising a number of [[Physics:Solar cell|solar cell]]s, which generate electrical power. PV installations may be ground-mounted, rooftop-mounted, wall-mounted or floating. The mount may be fixed or use a [[Physics:Solar tracker|solar tracker]] to follow the sun across the sky.

Photovoltaic technology helps to [[Earth:Climate change mitigation|mitigate climate change]] because it emits much less [[Earth:Carbon dioxide in Earth's atmosphere|carbon dioxide]] than fossil fuels. Solar PV has specific advantages as an energy source: once installed, its operation does not generate any pollution or any [[Chemistry:Greenhouse gas|greenhouse gas emissions]]; it shows scalability in respect of power needs and silicon has large availability in the Earth's crust, although other materials required in PV system manufacture such as silver may constrain further growth in the technology. Other major constraints identified include competition for land use.<ref name=Mayumi2017>{{cite journal |first1=Samuele |last1=Lo Piano |first2= Kozo |last2=Mayumi  |title= Toward an integrated assessment of the performance of photovoltaic systems for electricity generation |journal=Applied Energy |volume=186 |issue=2 |pages=167–74 |year=2017 |doi=10.1016/j.apenergy.2016.05.102 |s2cid=156783885 |url=https://zenodo.org/record/976281 }}</ref> The use of PV as a main source requires [[Engineering:Energy storage|energy storage]] systems or global distribution by high-voltage direct current power lines causing additional costs, and also has a number of other specific disadvantages such as variable power generation which have to be balanced. Production and installation does cause some pollution and [[Chemistry:Greenhouse gas|greenhouse gas emissions]], though only a fraction of the emissions caused by fossil fuels.

Photovoltaic systems have long been used in specialized applications as stand-alone installations and grid-connected PV systems have been in use since the 1990s.<ref name=reconsidering /> Photovoltaic modules were first mass-produced in 2000, when the German government funded a one hundred thousand roof program.<ref name="Solar Power for the World: What You Wanted to Know about Photovoltaics">{{cite book|author=Palz, Wolfgang |title=Solar Power for the World: What You Wanted to Know about Photovoltaics|url={{google books |plainurl=y |id=qGXvAgAAQBAJ|page=131}} |date= 2013|publisher=CRC Press|isbn=978-981-4411-87-5|pages=131–}}</ref> Decreasing costs has allowed PV to grow as an energy source. This has been partially driven by massive Chinese government investment in developing solar production capacity since 2000, and achieving [[Finance:Economies of scale|economies of scale]]. Improvements in manufacturing technology and efficiency have also led to decreasing costs.<ref name="our-world-in-data-pv-2020">{{cite web |title=Why did renewables become so cheap so fast? |url=https://ourworldindata.org/cheap-renewables-growth |publisher=[[Organization:Our World in Data|Our World in Data]] |date=December 1, 2020}}</ref><ref name="Shubbak2019">{{cite journal |last1=Shubbak |first1=Mahmood H. |title=The technological system of production and innovation: The case of photovoltaic technology in China |journal=Research Policy |date=2019 |volume=48 |issue=4 |pages=993–1015 |doi=10.1016/j.respol.2018.10.003|s2cid=158742469 |url=https://media.suub.uni-bremen.de/handle/elib/4421 }}</ref> [[Finance:Net metering|Net metering]] and financial incentives, such as preferential feed-in tariffs for solar-generated electricity, have supported solar PV installations in many countries.<ref>Renewable Energy Policy Network for the 21st century (REN21), [http://www.ren21.net/REN21Activities/GlobalStatusReport.aspx Renewables 2010 Global Status Report] {{Webarchive|url=https://web.archive.org/web/20140913111511/http://www.ren21.net/ren21activities/globalstatusreport.aspx |date=13 September 2014 }}, Paris, 2010, pp. 1–80.</ref> Panel prices dropped by a factor of 4 between 2004 and 2011. Module prices dropped by about 90% over the 2010s.

In 2022, worldwide installed PV capacity increased to more than 1 [[Terawatt|terawatt]] (TW) covering nearly two percent of global [[Physics:Electric energy consumption|electricity demand]].<ref name="fraunhofer-pv-report-2020-p4">{{cite web |title=PHOTOVOLTAICS REPORT |url=https://www.ise.fraunhofer.de/content/dam/ise/de/documents/publications/studies/Photovoltaics-Report.pdf |publisher=[[Organization:Fraunhofer Institute for Solar Energy Systems|Fraunhofer Institute for Solar Energy Systems]] |date=16 September 2020 |page=4}}</ref> After hydro and wind powers, PV is the third [[Engineering:Renewable energy|renewable energy]] source in terms of global capacity. In 2022, the [[Organization:International Energy Agency|International Energy Agency]] expected a growth by over 1&nbsp;TW from 2022 to 2027.<ref>{{cite web |title=Renewables 2019 |url=https://www.iea.org/reports/renewables-2019 |publisher=IEA |access-date=26 January 2020}}</ref> In some instances, PV has offered the cheapest source of electrical power in regions with a high solar potential, with a bid for pricing as low as 0.015&nbsp;US$/kWh in Qatar in 2023.<ref>{{cite web |title=KAHRAMAA and Siraj Energy Sign Agreements for Al-Kharsaah Solar PV Power Plant |url=https://www.km.qa/MediaCenter/pages/NewsDetails.aspx?ItemID=330 |publisher=Qatar General Electricity & Water Corporation "KAHRAMAA" |date=20 January 2020 |access-date=26 January 2020}}</ref> In 2023, the [[Organization:International Energy Agency|International Energy Agency]] stated in its World Energy Outlook that '[f]or projects with low cost financing that tap high quality resources, solar PV is now the cheapest source of electricity in history.<ref>Sunil Prasad Lohani, Andrew Blakers: ''100% renewable energy with pumped-hydro-energy storage in Nepal''. In: Clean Energy 5, 2, 2021, 243–253, {{doi|10.1093/ce/zkab011}}.</ref>

== Etymology ==

The term "photovoltaic" comes from the [[Social:Greek language|Greek]] {{Lang|grc|φῶς}} ({{Transliteration|grc|phōs}}) meaning "light", and from "volt", the unit of electromotive force, the [[Volt|volt]], which in turn comes from the last name of the Italian physicist [[Biography:Alessandro Volta|Alessandro Volta]], inventor of the battery ([[Chemistry:Electrochemical cell|electrochemical cell]]). The term "photovoltaic" has been in use in English since 1849.<ref>{{cite book |title=Elements of electro-biology,: or the voltaic mechanism of man; of electro-pathology, especially of the nervous system; and of electro-therapeutics |author=Smee, Alfred |publication-place=London |publisher=Longman, Brown, Green, and Longmans |page=15 |year=1849 |url={{google books |plainurl=y |id=CU0EAAAAQAAJ|page=15}}}}</ref>

== History ==
[[File:190903 - George Cove - solar photovoltaic panel - The Technical World Magazine.jpg |thumb |upright=1.2 |George Cove's solar panel pictured in ''The Technical World Magazine'' in March 1909.<ref name=TechnicalWorldMagazine_190903>{{cite magazine |title=The Latest Type of Solar Electric Generator |url=https://archive.org/details/technicalworldm02unkngoog/page/356/mode/2up |magazine=The Technical World Magazine |date=March 1909 |page=358}}</ref>]]
George Cove may have invented a photovoltaic panel in 1909, roughly 40 years before [[Organization:Bell Labs|Bell Labs]] did in 1950.<ref>{{Cite web|title=How to Build a Low-tech Solar Panel?|url=https://www.lowtechmagazine.com/2021/10/how-to-build-a-low-tech-solar-panel.html|access-date=2021-10-20|website=LOW-TECH MAGAZINE}}</ref> In 1989, the German Research Ministry initiated the first ever program to finance PV roofs (2200 roofs). A program led by Walter Sandtner in Bonn, Germany.<ref>{{Cite book |last=Palz |first=Wolfgang |url=https://books.google.com/books?id=qGXvAgAAQBAJ&pg=PA131 |title=Solar Power for the World: What You Wanted to Know about Photovoltaics |date=2013-10-21 |publisher=CRC Press |isbn=978-981-4411-87-5 |language=en}}</ref>

In 1994, Japan followed in their footsteps and conducted a similar program with 539 residential PV systems installed.<ref>{{Cite web |last=Noguchi |first=Masa |title=Number of Residential PV Installation in Japan: 1994-2003 |url=https://www.researchgate.net/figure/Number-of-Residential-PV-Installation-in-Japan-1994-2003_tbl1_228931649}}</ref> Since, many countries have continued to produce and finance PV systems in an exponential speed.

== Solar cells ==
{{Main|Physics:Solar cell}}
[[File:Solar cell.png|right|thumb|upright=1.2|Solar cells generate electricity directly from sunlight.]]
[[File:World PVOUT Solar-resource-map GlobalSolarAtlas World-Bank-Esmap-Solargis.png|upright=1.2|alt=Photovoltaic power potential map|thumb|Photovoltaic power potential map estimates, how many kWh of electricity can be produced from a 1 kWp free-standing c-Si modules, optimally inclined towards the Equator. The resulting long-term average is calculated based on weather data of at least 10 recent years.]]
Photovoltaics are best known as a method for generating [[Physics:Electric power|electric power]] by using [[Physics:Solar cell|solar cell]]s to convert energy from the sun into a flow of electrons by the [[Chemistry:Photovoltaic effect|photovoltaic effect]].<ref>[http://www.mrsolar.com/content/photovoltaic_effect.php Photovoltaic Effect] {{webarchive|url=https://web.archive.org/web/20110714123052/http://www.mrsolar.com/content/photovoltaic_effect.php |date=14 July 2011 }}. Mrsolar.com. Retrieved 12 December 2010</ref><ref>[http://encyclobeamia.solarbotics.net/articles/photovoltaic.html The photovoltaic effect] {{webarchive|url=https://web.archive.org/web/20101012011203/http://encyclobeamia.solarbotics.net/articles/photovoltaic.html |date=12 October 2010 }}. Encyclobeamia.solarbotics.net. Retrieved on 12 December 2010.</ref>

Solar cells produce direct current electricity from sunlight which can be used to power equipment or to [[Engineering:Rechargeable battery|recharge batteries]]. The first practical application of photovoltaics was to power orbiting [[Astronomy:Satellite|satellite]]s and other [[Engineering:Spacecraft|spacecraft]], but today the majority of photovoltaic modules are used for grid-connected systems for power generation. In this case an inverter is required to convert the [[Physics:Direct current|DC]] to [[Physics:Alternating current|AC]]. There is still a smaller market for stand alone systems for remote dwellings, [[Engineering:Electric boat|boats]], recreational vehicles, [[Engineering:Electric car|electric car]]s, roadside emergency telephones, [[Earth:Remote sensing|remote sensing]], and [[Physics:Cathodic protection|cathodic protection]] of [[Physics:Pipeline transport|pipelines]].

Photovoltaic power generation employs solar modules composed of a number of [[Physics:Solar cell|solar cell]]s containing a semiconductor material.<ref name=jac>{{cite journal|author=Jacobson, Mark Z.|year=2009|doi=10.1039/B809990C |bibcode=2009GeCAS..73R.581J|title=Review of Solutions to Global Warming, Air Pollution, and Energy Security|url=http://www.stanford.edu/group/efmh/jacobson/Articles/I/revsolglobwarmairpol.htm|journal=Energy & Environmental Science|volume=2|issue=2|pages=148–173|citeseerx=10.1.1.180.4676}}</ref> [[Physics:Copper in renewable energy#Photovoltaic system configurations|Copper solar cables]] connect modules (module cable), arrays (array cable), and sub-fields. Because of the growing demand for [[Engineering:Renewable energy|renewable energy]] sources, the manufacturing of solar cells and [[Physics:Photovoltaic system|photovoltaic arrays]] has advanced considerably in recent years.<ref name="German PV market">[http://www.solarbuzz.com/FastFactsGermany.htm German PV market]. Solarbuzz.com. Retrieved on 3 June 2012.</ref><ref name="renewableenergyaccess.com">[http://www.renewableenergyaccess.com/rea/news/story?id=47861 BP Solar to Expand Its Solar Cell Plants in Spain and India] {{webarchive|url=https://web.archive.org/web/20070926231054/http://www.renewableenergyaccess.com/rea/news/story?id=47861 |date=26 September 2007 }}. Renewableenergyaccess.com. 23 March 2007. Retrieved on 3 June 2012.</ref><ref name="technologyreview.com">Bullis, Kevin (23 June 2006). [http://www.technologyreview.com/read_article.aspx?id=17025&ch=biztech Large-Scale, Cheap Solar Electricity]. Technologyreview.com. Retrieved on 3 June 2012.</ref>

Cells require protection from the environment and are usually packaged tightly in solar modules.

Photovoltaic module power is measured under standard test conditions (STC) in "W<sub>p</sub>" ([[Watt-peak|watts peak]]).<ref>{{cite book | title = Handbook of Photovoltaic Science and Engineering |author1=Luque, Antonio  |author2=Hegedus, Steven  |name-list-style=amp | url = {{google books |plainurl=y |id=u-bCMhl_JjQC|page=326}} | publisher = John Wiley and Sons | year = 2003 | isbn = 978-0-471-49196-5}}</ref> The actual power output at a particular place may be less than or greater than this rated value, depending on geographical location, time of day, weather conditions, and other factors.<ref>[http://gisatnrel.nrel.gov/PVWatts_Viewer/index.html The PVWatts Solar Calculator] Retrieved on 7 September 2012</ref> Solar photovoltaic array [[Engineering:Capacity factor|capacity factor]]s are typically under 25% when not coupled with storage, which is lower than many other industrial sources of electricity.<ref>[http://www.remenergyco.com/why-solar-now Massachusetts: a Good Solar Market] {{webarchive|url=https://web.archive.org/web/20120912040953/http://www.remenergyco.com/why-solar-now |date=12 September 2012 }}. Remenergyco.com. Retrieved on 31 May 2013.</ref>

===Solar cell efficiencies===
{{Excerpt|Solar cell efficiency}}

== Performance and degradation ==
[[File:Variability of Solar Energy.jpg|thumb|This chart illustrates the effect of clouds on solar energy production.]]

Module performance is generally rated under standard test conditions (STC): [[Physics:Irradiance|irradiance]] of 1,000 W/m<sup>2</sup>, solar [[Spectrum|spectrum]] of AM 1.5 and module temperature at 25&nbsp;°C.<ref>{{Cite book|last=Dunlop|first=James P.|title=Photovoltaic systems|date=2012|publisher=American Technical Publishers, Inc|others=National Joint Apprenticeship and Training Committee for the Electrical Industry|isbn=978-1-935941-05-7|edition=3rd|location=Orland Park, IL|oclc=828685287}}</ref> The actual voltage and current output of the module changes as lighting, temperature and load conditions change, so there is never one specific voltage at which the module operates. Performance varies depending on geographic location, time of day, the day of the year, amount of [[Astronomy:Solar irradiance|solar irradiance]], direction and tilt of modules, cloud cover, shading, [[Astronomy:Soiling (solar energy)|soiling]], state of charge, and temperature. Performance of a module or panel can be measured at different time intervals with a DC clamp meter or shunt and logged, graphed, or charted with a chart recorder or data logger.

For optimum performance, a solar panel needs to be made of similar modules oriented in the same direction perpendicular to direct sunlight. Bypass diodes are used to circumvent broken or shaded panels and optimize output. These bypass diodes are usually placed along groups of solar cells to create a continuous flow.<ref>{{cite web |last1=Bowden |first1=Stuart |last2=Honsberg |first2=Christiana |title=Bypass Diodes |url=https://www.pveducation.org/pvcdrom/modules-and-arrays/bypass-diodes |website=Photovoltaic Education |access-date=29 June 2021}}</ref>

Electrical characteristics include nominal power (P<sub>MAX</sub>, measured in [[Watt|W]]), [[Physics:Open-circuit voltage|open-circuit voltage]] (V<sub>OC</sub>), short-circuit current (I<sub>SC</sub>, measured in [[Ampere|ampere]]s), maximum power voltage (V<sub>MPP</sub>), maximum power current (I<sub>MPP</sub>), peak power ([[Watt-peak|watt-peak]], W<sub>p</sub>), and module efficiency (%).

[[Physics:Open-circuit voltage|Open-circuit voltage]] or V<sub>OC</sub> is the maximum voltage the module can produce when not connected to an electrical circuit or system.<ref>{{cite web |title=Open-Circuit Voltage (Battery) |url=https://electricalschool.org/open-circuitvoltagebattery/ |website=Electrical School |date=13 June 2018 |access-date=30 June 2021}}</ref> V<sub>OC</sub> can be measured with a [[Engineering:Voltmeter|voltmeter]] directly on an illuminated module's terminals or on its disconnected cable.

The peak power rating, W<sub>p</sub>, is the maximum output under standard test conditions (not the maximum possible output). Typical modules, which could measure approximately {{convert|1|x|2|m|ft|sigfig=1}}, will be rated from as low as 75&nbsp;W to as high as 600&nbsp;W, depending on their efficiency. At the time of testing, the test modules are binned according to their test results, and a typical manufacturer might rate their modules in 5&nbsp;W increments, and either rate them at +/- 3%, +/-5%, +3/-0% or +5/-0%.<ref>{{cite web|title=REC Alpha Black Series Factsheet|url=https://commercialsolaraustralia.com.au/wp-content/uploads/2020/08/DS-REC-Alpha-Black-Series-Rev-D-IEC-PRINT-EN.pdf}}</ref><ref>{{cite web |url=http://www.trinasolar.com/images/PDF/datasheets/us/TSM-PA14_US.pdf |title=TSM PC/PM14 Datasheet |access-date=2012-06-04 |archive-url=https://web.archive.org/web/20131029200512/http://www.trinasolar.com/images/PDF/datasheets/us/TSM-PA14_US.pdf |archive-date=29 October 2013  }}</ref><ref>{{cite web |url=https://www.lubisolar.com/wp-content/uploads/2018/03/Poly-260-275W.pdf |title=LBS Poly 260 275 Data sheet |access-date=2018-01-09 |archive-date=9 January 2019 |archive-url=https://web.archive.org/web/20190109155544/https://www.lubisolar.com/wp-content/uploads/2018/03/Poly-260-275W.pdf |url-status=dead }}</ref>

=== Influence of temperature ===

The performance of a photovoltaic (PV) module depends on the environmental conditions, mainly on the global incident irradiance G in the plane of the module. However, the temperature T of the p–n junction also influences the main electrical parameters: the short circuit current ISC, the open circuit voltage VOC and the maximum power Pmax. In general, it is known that VOC shows a significant inverse correlation with T, while for ISC this correlation is direct, but weaker, so that this increase does not compensate for the decrease in VOC. As a consequence, Pmax decreases when T increases. This correlation between the power output of a solar cell and the working temperature of its junction depends on the semiconductor material, and is due to the influence of T on the concentration, lifetime, and mobility of the intrinsic carriers, i.e., electrons and gaps. inside the photovoltaic cell.

Temperature sensitivity is usually described by temperature coefficients, each of which expresses the derivative of the parameter to which it refers with respect to the junction temperature. The values of these parameters, which can be found in any data sheet of the photovoltaic module, are the following:

- β: VOC variation coefficient with respect to T, given by ∂VOC/∂T.

- α: Coefficient of variation of ISC with respect to T, given by ∂ISC/∂T.

- δ: Coefficient of variation of Pmax with respect to T, given by ∂Pmax/∂T.

Techniques for estimating these coefficients from experimental data can be found in the literature <ref>{{cite book|doi=10.1002/pip.3396|title =Temperature coefficients of degraded crystalline silicon photovoltaic modules at outdoor conditions|year=2021|last1=Piliougine|first1=M.|last2=Oukaja|first2=A.|last3=Sidrach‐de‐Cardona|first3=M.|last4= Spagnuolo|first4=G.|work=Progress in Photovoltaics |volume=29 |issue=5 |pages=558–570 |s2cid=233976803 }}</ref>

===Degradation===

The ability of solar modules to withstand damage by rain, [[Earth:Hail|hail]], heavy snow load, and cycles of heat and cold varies by manufacturer, although most solar panels on the U.S. market are UL listed, meaning they have gone through testing to withstand hail.<ref>{{Cite news|url=http://energyinformative.org/solar-panels-weather/|title=Are Solar Panels Affected by Weather? - Energy Informative|work=Energy Informative|access-date=2018-03-14|language=en-US}}</ref>

[[Physics:Potential-induced degradation|Potential-induced degradation]] (also called PID) is a potential-induced performance degradation in crystalline photovoltaic modules, caused by so-called stray currents.<ref>{{Cite web|url=https://www.solarplaza.com/channels/asset-management/11674/potential-induced-degradation-combatting-phantom-menace/|title=Solarplaza Potential Induced Degradation: Combatting a Phantom Menace|website=www.solarplaza.com|language=en|access-date=2017-09-04}}</ref> This effect may cause power loss of up to 30%.<ref>{{Cite web|url=https://eicero.com/what-is-pid|title=What is PID? — eicero|last=(www.inspire.cz)|first=INSPIRE CZ s.r.o.|website=eicero.com|language=en|access-date=2017-09-04|archive-date=4 September 2017|archive-url=https://web.archive.org/web/20170904105326/https://eicero.com/what-is-pid|url-status=dead}}</ref>

The largest challenge for photovoltaic technology is the purchase price per watt of electricity produced. Advancements in photovoltaic technologies have brought about the process of "doping" the silicon substrate to lower the activation energy thereby making the panel more efficient in converting photons to retrievable electrons.<ref>{{cite web |title=How Solar Cells Work |url=http://science.howstuffworks.com/environmental/energy/solar-cell2.htm |website=HowStuffWorks |date=April 2000 |access-date=2015-12-09}}</ref>

Chemicals such as [[Chemistry:Boron|boron]] (p-type) are applied into the semiconductor crystal in order to create donor and acceptor energy levels substantially closer to the valence and conductor bands.<ref>{{cite web |title=Bonding in Metals and Semiconductors |url=http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/s16-06-bonding-in-metals-and-semicond.html |website=2012books.lardbucket.org|access-date=2015-12-09}}</ref> In doing so, the addition of boron impurity allows the activation energy to decrease twenty-fold from 1.12&nbsp;eV to 0.05&nbsp;eV. Since the potential difference (E<sub>B</sub>) is so low, the boron is able to thermally ionize at room temperatures. This allows for free energy carriers in the conduction and valence bands thereby allowing greater conversion of photons to electrons.

The power output of a photovoltaic (PV) device decreases over time. This decrease is due to its exposure to solar radiation as well as other external conditions. The degradation index, which is defined as the annual percentage of output power loss, is a key factor in determining the long-term production of a photovoltaic plant. To estimate this degradation, the percentage of decrease associated with each of the electrical parameters. The individual degradation of a photovoltaic module can significantly influence the performance of a complete string. Furthermore, not all modules in the same installation decrease their performance at exactly the same rate. Given a set of modules exposed to long-term outdoor conditions, the individual degradation of the main electrical parameters and the increase in their dispersion must be considered. As each module tends to degrade differently, the behavior of the modules will be increasingly different over time, negatively affecting the overall performance of the plant.

There are several studies dealing with the power degradation analysis of modules based on different photovoltaic technologies available in the literature. According to a recent study,<ref>{{cite journal|title=Analysis of the degradation of single-crystalline silicon modules after 21 years of operation|year=2021| last1=Piliougine|first1=M.|last2=Oukaja|first2=A.|last3=Sánchez-Friera|first3=P.|last4=Petrone|first4=G.|last5=Sánchez-Pacheco|first5=J.F.|last6= Spagnuolo|first6=G.|last7=Sidrach-de-Cardona|first7=M.|journal=Progress in Photovoltaics: Research and Applications |series=Progress in Photovoltaics |volume=29 |issue=8 |pages=907–919 |doi=10.1002/pip.3409 |s2cid=234831264 }}</ref> the degradation of crystalline silicon modules is very regular, oscillating between 0.8% and 1.0% per year.

On the other hand, if we analyze the performance of thin-film photovoltaic modules, an initial period of strong degradation is observed (which can last several months and up to two years), followed by a later stage in which the degradation stabilizes, being then comparable to that of crystalline silicon.<ref>{{cite journal|title=Analysis of the degradation of amorphous silicon-based modules after 11 years of exposure by means of IEC60891:2021 procedure 3|year=2022|last1=Piliougine|first1=M.|last2=Oukaja|first2=A.|last3=Sidrach‐de‐Cardona|first3=M.|last4=Spagnuolo|first4 =G.|journal=Progress in Photovoltaics: Research and Applications |series=Progress in Photovoltaics |volume=30 |issue=10 |pages=1176–1187 |doi=10.1002/pip.3567 |hdl=10630/24064 |s2cid=248487635 |hdl-access=free}}</ref> Strong seasonal variations are also observed in such thin-film technologies because the influence of the solar spectrum is much greater. For example, for modules of amorphous silicon, micromorphic silicon or cadmium telluride, we are talking about annual degradation rates for the first years of between 3% and 4%.<ref>{{cite journal|doi=10.1016/j.renene.2022.05.063|title=New model to study the outdoor degradation of thin-film photovoltaic modules|year=2022|last1=Piliougine|first1=M.|last2=Sánchez-Friera|first2 =P.|last3=Petrone|first3=G.|last4=Sánchez-Pacheco|first4=J.F.|last5=Spagnuolo|first5=G.|last6=Sidrach-de-Cardona|first6=M.|journal=Renewable Energy|volume=193 |pages=857–869 |s2cid=248926054 }}</ref> However, other technologies, such as CIGS, show much lower degradation rates, even in those early years.

== Manufacturing of PV systems==
Overall the manufacturing process of creating solar photovoltaics is simple in that it does not require the culmination of many complex or moving parts. Because of the solid-state nature of PV systems, they often have relatively long lifetimes, anywhere from 10 to 30 years. To increase the electrical output of a PV system, the manufacturer must simply add more photovoltaic components. Because of this, economies of scale are important for manufacturers as costs decrease with increasing output.<ref>{{Cite journal|title = U.S. Solar Photovoltaic Manufacturing: Industry Trends, Global Competition, Federal Support|last = Platzer|first = Michael|date = January 27, 2015|journal = Congressional Research Service}}</ref>

While there are many types of PV systems known to be effective, crystalline silicon PV accounted for around 90% of the worldwide production of PV in 2013. Manufacturing silicon PV systems has several steps. First, polysilicon is processed from mined quartz until it is very pure (semi-conductor grade). This is melted down when small amounts of [[Chemistry:Boron|boron]], a group III element, are added to make a p-type semiconductor rich in electron holes. Typically using a seed crystal, an ingot of this solution is grown from the liquid polycrystalline. The ingot may also be cast in a mold. Wafers of this semiconductor material are cut from the bulk material with wire saws, and then go through surface etching before being cleaned. Next, the wafers are placed into a phosphorus vapor deposition furnace which lays a very thin layer of phosphorus, a group V element, which creates an n-type semiconducting surface. To reduce energy losses, an anti-reflective coating is added to the surface, along with electrical contacts. After finishing the cell, cells are connected via electrical circuit according to the specific application and prepared for shipping and installation.<ref>{{cite web|title = How PV Cells Are Made|url = http://www.fsec.ucf.edu/en/consumer/solar_electricity/basics/how_cells_made.htm|website = www.fsec.ucf.edu|access-date = 2015-11-05}}</ref>

===Environmental costs of manufacture===
Solar photovoltaic power is not entirely "clean energy": production produces greenhouse gas emissions, materials used to build the cells are potentially unsustainable and will run out eventually, the technology uses toxic substances which cause pollution, and there are no viable technologies for recycling solar waste.<ref>{{cite web|url=http://environmentalprogress.org/big-news/2017/6/21/are-we-headed-for-a-solar-waste-crisis|title=Are we headed for a solar waste crisis?|website=Environmentalprogress.org|date=21 June 2017 |access-date=30 December 2017}}</ref> Data required to investigate their impact are sometimes affected by a rather large amount of uncertainty. The values of human labor and water consumption, for example, are not precisely assessed due to the lack of systematic and accurate analyses in the scientific literature.<ref name=Mayumi2017/> One difficulty in determining effects due to PV is to determine if the wastes are released to the air, water, or soil during the manufacturing phase.<ref name=":4">{{cite journal|author=Fthenakis, V. M., Kim, H. C. & Alsema, E.|doi=10.1021/es071763q |pmid=18409654 |title=Emissions from photovoltaic life cycles|journal= Environmental Science & Technology |volume=42|issue=6 |pages= 2168–2174 |year=2008|bibcode=2008EnST...42.2168F |hdl=1874/32964 |s2cid=20850468 |hdl-access=free }}</ref> Life-cycle assessments, which look at all different environment effects ranging from [[Physics:Global warming potential|global warming potential]], pollution, water depletion and others, are unavailable for PV. Instead, studies have tried to estimate the impact and potential impact of various types of PV, but these estimates are usually restricted to simply assessing energy costs of the manufacture and/or transport, because these are new technologies and the total environmental impact of their components and disposal methods are unknown, even for commercially available first generation solar cells, let alone experimental prototypes with no commercial viability.<ref name=":2">{{cite journal|author=Collier, J., Wu, S. & Apul, D.|title= Life cycle environmental impacts from CZTS (copper zinc tin sulfide) and Zn<sub>3</sub>P<sub>2</sub> (zinc phosphide) thin film PV (photovoltaic) cells|doi=10.1016/j.energy.2014.06.076|journal= Energy |volume=74|pages= 314–321 |year=2014}}</ref>

Thus, estimates of the environmental impact of PV have focused on carbon dioxide equivalents per kWh or energy pay-back time (EPBT). The EPBT describes the timespan a PV system needs to operate in order to generate the same amount of energy that was used for its manufacture.<ref name=Columbia2009>{{cite web|url=http://www.clca.columbia.edu/papers/Photovoltaic_Energy_Payback_Times.pdf |title=An analysis of the energy efficiency of photovoltaic cells in reducing {{CO2}} emissions |author=<!--Not stated--> |website=clca.columbia.edu |date=31 May 2009 |archive-date=25 March 2015 |archive-url= https://www.webcitation.org/6XIHtGrwz?url=http://www.clca.columbia.edu/papers/Photovoltaic_Energy_Payback_Times.pdf |url-status=live }}</ref> Another study includes transport energy costs in the EPBT.<ref name="fraunhofer-pv-report-2020-p36">{{cite web |title=PHOTOVOLTAICS REPORT |url=https://www.ise.fraunhofer.de/content/dam/ise/de/documents/publications/studies/Photovoltaics-Report.pdf |publisher=[[Organization:Fraunhofer Institute for Solar Energy Systems|Fraunhofer Institute for Solar Energy Systems]] |date=16 September 2020 |pages=36, 43, 46}}</ref> The EPBT has also been defined completely differently as "the time needed to compensate for the total renewable- and non-renewable primary energy required during the life cycle of a PV system" in another study, which also included installation costs.<ref name=":0">{{cite journal|author=Anctil, A., Babbitt, C. W., Raffaelle, R. P. & Landi, B. J. |doi=10.1002/pip.2226|title=Cumulative energy demand for small molecule and polymer photovoltaics|journal= Progress in Photovoltaics: Research and Applications |volume=21|issue=7|pages= 1541–1554 |year=2013|s2cid=94279905}}</ref> This energy amortization, given in years, is also referred to as ''break-even'' energy [[Finance:Payback period|payback time]].<ref name=Galarraga>{{cite book|url= https://books.google.com/books?id=N6rVrxV2ujMC&q=Energy+payback+period |title=Handbook of Sustainable Energy |author=Ibon Galarraga, M. González-Eguino, Anil Markandya |page=37|date=1 January 2011|publisher=Edward Elgar Publishing|access-date=9 May 2017|via=Google Books |isbn=978-0-85793-638-7}}</ref> The lower the EPBT, the lower the environmental cost of [[Engineering:Solar power|solar power]]. The EPBT depends vastly on the location where the PV system is installed (e.g. the amount of sunlight available and the efficiency of the electrical grid)<ref name="fraunhofer-pv-report-2020-p36"/> and on the type of system, namely the system's components.<ref name=Columbia2009/>

A 2015 review of EPBT estimates of first and second-generation PV suggested that there was greater variation in embedded energy than in efficiency of the cells implying that it was mainly the embedded energy that needs to reduce to have a greater reduction in EPBT.<ref name=":3">{{cite journal|author=Bhandari, K. P., Collier, J. M., Ellingson, R. J. & Apul, D. S. |doi=10.1016/j.rser.2015.02.057|title=Energy payback time (EPBT) and energy return on energy invested (EROI) of solar photovoltaic systems: A systematic review and meta-analysis|journal= Renewable and Sustainable Energy Reviews |volume=47|pages= 133–141 |year=2015}}</ref>

In general, the most important component of solar panels, which accounts for much of the energy use and greenhouse gas emissions, is the refining of the polysilicon.<ref name=Columbia2009/> As to how much percentage of the EPBT this silicon depends on the type of system. A fully autarkic system requires additional components ('Balance of System', the [[Engineering:Power inverter|power inverter]]s, storage, etc.) which significantly increase the energy cost of manufacture, but in a simple rooftop system, some 90% of the energy cost is from silicon, with the remainder coming from the inverters and module frame.<ref name=Columbia2009/>

In an analysis by Alsema ''et al''. from 1998, the energy payback time was higher than 10 years for the former system in 1997, while for a standard rooftop system the EPBT was calculated as between 3.5 and 8 years.<ref name=Columbia2009/><ref>{{cite web|url=http://mosaic.cnfolio.com/M528Coursework2009C112#Payback%20Time |title=An analysis of the energy efficiency of photovoltaic cells in reducing {{CO2}} emissions |quote=Energy Pay Back time comparison for Photovoltaic Cells (Alsema, Frankl, Kato, 1998, p. 5 |publisher=University of Portsmouth |date=31 May 2009 |archive-url=https://www.webcitation.org/6XIF0zvO1?url=http://mosaic.cnfolio.com/M528Coursework2009C112 |archive-date=25 March 2015 |url-status=live }}</ref>

The EPBT relates closely to the concepts of net energy gain (NEG) and energy returned on energy invested (EROI). They are both used in [[Physics:Energy economics|energy economics]] and refer to the difference between the energy expended to harvest an energy source and the amount of energy gained from that harvest. The NEG and EROI also take the operating lifetime of a PV system into account and a working life of 25 to 30 years is typically assumed. From these metrics, the Energy payback Time can be derived by calculation.<ref>{{cite web |url=http://www.bnl.gov/pv/files/pdf/241_Raugei_EROI_EP_revised_II_2012-03_VMF.pdf |title=The Energy Return on Energy Investment (EROI) of Photovoltaics: Methodology and Comparisons with Fossil Fuel Life Cycles |author1=Marco Raugei |author2=Pere Fullana-i-Palmer |author3=Vasilis Fthenakis |website=www.bnl.gov/ |date=March 2012 |archive-url=https://web.archive.org/web/20160308235118/https://www.bnl.gov/pv/files/pdf/241_Raugei_EROI_EP_revised_II_2012-03_VMF.pdf |archive-date=8 March 2016 |url-status=live}}</ref><ref>{{cite web |url=http://www.iea-pvps.org/fileadmin/dam/public/report/technical/rep12_11.pdf |title=Methodology Guidelines on Life Cycle Assessment of Photovoltaic Electricity |author=Vasilis Fthenakis |author2=Rolf Frischknecht |author3=Marco Raugei |author4=Hyung Chul Kim |author5=Erik Alsema |author6=Michael Held |author7=Mariska de Wild-Scholten |website=www.iea-pvps.org/ |publisher=IEA-PVPS |date=November 2011 |pages=8–10 |archive-url=https://web.archive.org/web/20150924032857/http://www.iea-pvps.org/fileadmin/dam/public/report/technical/rep12_11.pdf |archive-date=24 September 2015 |url-status=live}}</ref>

====EPBT improvements====

PV systems using crystalline silicon, by far the majority of the systems in practical use, have such a high EPBT because silicon is [[Chemistry:Silicon#Production|produced]] by the reduction of high-grade quartz sand in [[Physics:Electric arc furnace|electric furnaces]]. This coke-fired [[Engineering:Smelting|smelting]] process occurs at high temperatures of more than 1000&nbsp;°C and is very energy intensive, using about 11 kilowatt-hours (kWh) per produced kilogram of silicon.<ref name=si-production>{{cite web |title=Production Process of Silicon  |url=http://www.simcoa.com.au/production-process.html |website=www.simcoa.com.au  |publisher=Simcoa Operations |access-date=17 September 2014 |archive-url=https://web.archive.org/web/20140619182841/http://simcoa.com.au/production-process.html |archive-date=19 June 2014 }}</ref> The energy requirements of this process makes the energy cost per unit of silicon produced relatively inelastic, which means that the production process itself will not become more efficient in the future.

Nonetheless, the energy payback time has shortened significantly over the last years, as crystalline silicon cells became ever more efficient in converting sunlight, while the thickness of the wafer material was constantly reduced and therefore required less silicon for its manufacture. Within the last ten years, the amount of silicon used for solar cells declined from 16 to 6 grams per [[Watt-peak|watt-peak]]. In the same period, the thickness of a c-Si wafer was reduced from 300&nbsp;μm, or microns, to about 160–190&nbsp;μm. The [[Engineering:Wire saw|sawing techniques]] that slice crystalline silicon ingots into wafers have also improved by reducing the kerf loss and making it easier to recycle the silicon sawdust.<ref>{{cite web |publisher=Fraunhofer ISE, 24th European PV Solar Energy Conference and Exhibition |url=http://www.ise.fraunhofer.de/de/veroeffentlichungen/konferenzbeitraege/2009/24th-european-photovoltaic-solar-energy-conference-and-exhibition-hamburg-germany/schumann_2v.1.21.pdf |title=Reaching kerf loss below 100 μm by optimizations |date=September 2009}}</ref><ref>{{cite web |publisher=HZDR - Helmholtz-Zentrum Dresden-Rossendorf |url=https://www.hzdr.de/db/Cms?pNid=3165 |title=Silicon kerf loss recycling |date=4 April 2014}}</ref>

{| class="wikitable"
|+Key parameters for material and energy efficiency
|-
! Parameter !! Mono-Si !! CdTe
|-
| Cell efficiency || 16.5% || 15.6%
|-
| Derate cell to module efficiency || 8.5% || 13.9%
|-
| Module efficiency || 15.1% || 13.4%
|-
| Wafer thickness / layer thickness || 190&nbsp;μm || 4.0&nbsp;μm
|-
| Kerf loss || 190&nbsp;μm || &ndash;
|-
| Silver per cell || 9.6&nbsp;g/m<sup>2</sup> || &ndash;
|-
| Glass thickness || 4.0&nbsp;mm || 3.5&nbsp;mm
|-
| Operational lifetime || 30 years || 30 years
|-
! colspan=3 style="font-weight: normal; font-size: 0.85em; text-align: left; padding: 6px 2px 4px 4px;"  | Source: ''IEA-PVPS, Life Cycle Assessment, March 2015''<ref>{{cite web |title=Life Cycle Assessment of Future Photovoltaic Electricity Production from Residential-scale Systems Operated in Europe |url=http://www.iea-pvps.org/index.php?id=314 |publisher=IEA-PVPS |date=13 March 2015}}</ref>
|}

==== Effects from first generation PV ====

[[Chemistry:Crystalline silicon|Crystalline silicon]] modules are the most extensively studied PV type in terms of LCA since they are the most commonly used. Mono-crystalline silicon photovoltaic systems (mono-si) have an average efficiency of 14.0%.<ref name=":5">Life Cycle Greenhouse Gas Emissions from Solar Photovoltaics, National Renewable Energy Laboratory, U.S. Department of Energy, 2012, 1–2.</ref> The cells tend to follow a structure of front electrode, anti-reflection film, n-layer, p-layer, and back electrode, with the sun hitting the front electrode. EPBT ranges from 1.7 to 2.7 years.<ref name=":6">{{cite journal|author=Krebs, F. C. |title=Fabrication and processing of polymer solar cells: a review of printing and coating techniques|doi=10.1016/j.solmat.2008.10.004|journal= Solar Energy Materials and Solar Cells |volume=93|issue=4|pages= 394–412 |year=2009}}</ref> The cradle to gate of CO<sub>2</sub>-eq/kWh ranges from 37.3 to 72.2 grams when installed in Southern Europe.<ref name=":7">{{cite journal|author1=Yue D.|author2=You F.|author3=Darling S. B. |title=Domestic and overseas manufacturing scenarios of silicon-based photovoltaics: Life cycle energy and environmental comparative analysis|doi=10.1016/j.solener.2014.04.008|journal= Solar Energy |volume=105|pages= 669–678 |year=2014|bibcode=2014SoEn..105..669Y}}</ref>

Techniques to produce multi-crystalline silicon (multi-si) photovoltaic cells are simpler and cheaper than mono-si, however tend to make less efficient cells, an average of 13.2%.<ref name=":5" /> EPBT ranges from 1.5 to 2.6 years.<ref name=":6" /> The cradle to gate of CO<sub>2</sub>-eq/kWh ranges from 28.5 to 69 grams when installed in Southern Europe.<ref name=":7" />

Assuming that the following countries had a high-quality grid infrastructure as in Europe, in 2020 it was calculated it would take 1.28 years in [[Place:Ottawa|Ottawa]], Canada, for a [[Physics:Rooftop photovoltaic power station|rooftop photovoltaic system]] to produce the same amount of energy as required to manufacture the silicon in the modules in it (excluding the silver, glass, mounts and other components), 0.97 years in Catania, Italy, and 0.4 years in Jaipur, India. Outside of Europe, where net grid efficiencies are lower, it would take longer. This '[[Chemistry:Crystalline silicon#Energy payback time|energy payback time]]' can be seen as the portion of time during the useful lifetime of the module in which the energy production is polluting. At best, this means that a 30-year old panel has produced clean energy for 97% of its lifetime, or that the silicon in the modules in a solar panel produce 97% less greenhouse gas emissions than a coal-fired plant for the same amount of energy (assuming and ignoring many things).<ref name="fraunhofer-pv-report-2020-p36"/> Some studies have looked beyond EPBT and GWP to other environmental effects. In one such study, conventional energy mix in Greece was compared to multi-si PV and found a 95% overall reduction in effects including carcinogens, eco-toxicity, acidification, eutrophication, and eleven others.<ref>{{cite journal|author1=Gaidajis, G.  |author2=Angelakoglou, K. |name-list-style=amp |doi=10.1080/10286608.2012.710608 |title=Environmental performance of renewable energy systems with the application of life-cycle assessment: a multi-Si photovoltaic module case study|journal=Civil Engineering and Environmental Systems |volume=29|issue=4 |pages= 231–238 |year=2012|s2cid=110058349 }}</ref>

==== Impact from second generation PV ====

[[Physics:Cadmium telluride photovoltaics|Cadmium telluride]] (CdTe) is one of the fastest-growing [[Engineering:Thin-film solar cell|thin film based solar cells]] which are collectively known as second-generation devices. This new thin-film device also shares similar performance restrictions ([[Physics:Shockley–Queisser limit|Shockley-Queisser efficiency limit]]) as conventional Si devices but promises to lower the cost of each device by both reducing material and energy consumption during manufacturing. The global market share of CdTe was 4.7% in 2008.<ref name=":4" /> This technology's highest power conversion efficiency is 21%.<ref>Photovoltaics Report. (Fraunhofer Institute for Solar Energy Systems, ISE, 2015).</ref> The cell structure includes glass substrate (around 2&nbsp;mm), transparent conductor layer, CdS buffer layer (50–150&nbsp;nm), CdTe absorber and a metal contact layer.

CdTe PV systems require less energy input in their production than other commercial PV systems per unit electricity production. The average CO<sub>2</sub>-eq/kWh is around 18 grams (cradle to gate). CdTe has the fastest EPBT of all commercial PV technologies, which varies between 0.3 and 1.2 years.<ref name=":8">{{cite journal|author1=Goe, M.  |author2=Gaustad, G.  |name-list-style=amp |title=Strengthening the case for recycling photovoltaics: An energy payback analysis|doi=10.1016/j.apenergy.2014.01.036|journal= Applied Energy |volume=120|pages= 41–48 |year=2014}}</ref>

==== Effects from third generation PV ====

Third-generation PVs are designed to combine the advantages of both the first and second generation devices and they do not have Shockley-Queisser limit, a theoretical limit for first and second generation PV cells. The thickness of a third generation device is less than 1&nbsp;μm.<ref>{{cite journal|author1=Brown, G. F.  |author2=Wu, J.  |name-list-style=amp |title=Third generation photovoltaics|doi=10.1002/lpor.200810039|journal= Laser & Photonics Reviews |volume=3|issue=4|pages= 394–405 |year=2009|bibcode=2009LPRv....3..394B|s2cid=13179665 |url=https://directory.doabooks.org/handle/20.500.12854/65801 }}</ref>

Two new promising thin film technologies are copper zinc tin sulfide (Cu<sub>2</sub>ZnSnS<sub>4</sub> or CZTS),<ref name=":2" /> [[Chemistry:Zinc phosphide|zinc phosphide]] (Zn<sub>3</sub>P<sub>2</sub>)<ref name=":2" /> and single-walled carbon nano-tubes (SWCNT).<ref name="Celik, I. 2017">Celik, I., Mason, B. E., Phillips, A. B., Heben, M. J., & Apul, D. S. (2017). Environmental Impacts from Photovoltaic Solar Cells Made with Single Walled Carbon Nanotubes. Environmental Science & Technology.</ref> These thin films are currently only produced in the lab but may be commercialized in the future. The manufacturing of CZTS and (Zn<sub>3</sub>P<sub>2</sub>) processes are expected to be similar to those of current thin film technologies of CIGS and CdTe, respectively. While the absorber layer of SWCNT PV is expected to be synthesized with CoMoCAT method.<ref>Agboola, A. E. Development and model formulation of scalable carbon nanotube processes: HiPCO and CoMoCAT process models;Louisiana State University, 2005.</ref> by Contrary to established thin films such as CIGS and CdTe, CZTS, Zn<sub>3</sub>P<sub>2</sub>, and SWCNT PVs are made from earth abundant, nontoxic materials and have the potential to produce more electricity annually than the current worldwide consumption.<ref>{{cite journal|author=Wadia, C., Alivisatos, A. P. & Kammen, D. M. |title=Materials Availability Expands the Opportunity for Large-Scale Photovoltaics Deployment|journal= Environmental Science and Technology |volume=43|issue=6|pages= 2072–2077 |year=2009|pmid=19368216 |doi=10.1021/es8019534|bibcode=2009EnST...43.2072W}}</ref><ref>{{cite journal|doi=10.1016/j.renene.2011.03.010|title=Abundant non-toxic materials for thin film solar cells: Alternative to conventional materials|journal=Renewable Energy|volume=36|issue=10|pages=2753–2758|year=2011|last1=Alharbi|first1=Fahhad|last2=Bass|first2=John D.|last3=Salhi|first3=Abdelmajid|last4=Alyamani|first4=Ahmed|last5=Kim|first5=Ho-Cheol|last6=Miller|first6=Robert D.}}</ref> While CZTS and Zn<sub>3</sub>P<sub>2</sub> offer good promise for these reasons, the specific environmental implications of their commercial production are not yet known. Global warming potential of CZTS and Zn<sub>3</sub>P<sub>2</sub> were found 38 and 30 grams CO<sub>2</sub>-eq/kWh while their corresponding EPBT were found 1.85 and 0.78 years, respectively.<ref name=":2" /> Overall, CdTe and Zn<sub>3</sub>P<sub>2</sub> have similar environmental effects but can slightly outperform CIGS and CZTS.<ref name=":2" /> A study on environmental impacts of SWCNT PVs by Celik et al., including an existing 1% efficient device and a theoretical 28% efficient device, found that, compared to monocrystalline Si, the environmental impacts from 1% SWCNT was ~18 times higher due mainly to the short lifetime of three years.<ref name="Celik, I. 2017"/>

== Economics ==

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There have been major changes in the underlying costs, industry structure and market prices of solar photovoltaics technology, over the years, and gaining a coherent picture of the shifts occurring across the industry value chain globally is a challenge. This is due to: "the rapidity of cost and price changes, the complexity of the PV supply chain, which involves a large number of manufacturing processes, the balance of system (BOS) and installation costs associated with complete PV systems, the choice of different distribution channels, and differences between regional markets within which PV is being deployed". Further complexities result from the many different policy support initiatives that have been put in place to facilitate photovoltaics commercialisation in various countries.<ref name=reconsidering />

Renewable energy technologies have generally gotten cheaper since their invention.<ref>[https://www.reuters.com/article/GCA-GreenBusiness/idUSTRE5AM2BE20091123 Renewable energy costs drop in '09] Reuters, 23 November 2009.</ref><ref>[http://www.sustainablebusiness.com/index.cfm/go/news.display/id/19297 Solar Power 50% Cheaper By Year End – Analysis]. ''Reuters'', 24 November 2009.</ref><ref name=SilverLining>{{cite web |url=http://www.renewableenergyworld.com/rea/news/article/2011/08/a-silver-lining-in-declining-solar-prices |title=A Silver Lining in Declining Solar Prices |author=Harris, Arno |date=31 August 2011|website=Renewable Energy World}}</ref> Renewable energy systems have become cheaper to build than fossil fuel power plants across much of the world, thanks to advances in wind and solar energy technology, in particular.<ref>{{cite book |title=Renewable Power Generation Costs in 2019. |date=2020 |publisher=International Renewable Energy Agency |location=Abu Dhabi |isbn=978-92-9260-244-4 |url=https://www.irena.org/publications/2020/Jun/Renewable-Power-Costs-in-2019}}</ref>

===Hardware costs===
[[File:1975 – Price of solar panels as a function of cumulative installed capacity.svg |thumb |[[Swanson's law|Swanson's law]]–stating that solar module prices have dropped about 20% for each doubling of installed capacity—defines the "learning curve" of solar photovoltaics.<ref name=OWID_PanelCostAndCapacity_2021>{{cite web |title=Solar (photovoltaic) panel prices vs. cumulative capacity |url=https://ourworldindata.org/grapher/solar-pv-prices-vs-cumulative-capacity |website=OurWorldInData.org |archive-url=https://archive.today/20230929225159/https://ourworldindata.org/grapher/solar-pv-prices-vs-cumulative-capacity |archive-date=29 September 2023 |date=2023 |url-status=live }} OWID credits source data to: Nemet (2009); Farmer & Lafond (2016); International Renewable Energy Agency (IRENA).</ref>]]
In 1977 crystalline silicon solar cell prices were at $76.67/W.<ref name="Econ1">{{cite news| date =21 November 2012|url=https://www.economist.com/news/21566414-alternative-energy-will-no-longer-be-alternative-sunny-uplands| title =Sunny Uplands: Alternative energy will no longer be alternative| publisher=The Economist| access-date = 28 December 2012}}</ref>

Although wholesale module prices remained flat at around $3.50 to $4.00/W in the early 2000s due to high demand in Germany and Spain afforded by generous subsidies and shortage of polysilicon, demand crashed with the abrupt ending of Spanish subsidies after the market crash of 2008, and the price dropped rapidly to $2.00/W. Manufacturers were able to maintain a positive operating margin despite a 50% drop in income due to innovation and reductions in costs. In late 2011, factory-gate prices for crystalline-silicon photovoltaic modules suddenly dropped below the $1.00/W mark, taking many in the industry by surprise, and has caused a number of solar manufacturing companies to go bankrupt throughout the world. The $1.00/W cost is often regarded in the PV industry as marking the achievement of grid parity for PV, but most experts do not believe this price point is sustainable. Technological advancements, manufacturing process improvements, and industry re-structuring, may mean that further price reductions are possible.<ref name=reconsidering>{{Cite journal | doi = 10.1016/j.renene.2012.11.029 | url = http://az2112.com/assets/energy-bnef_re_considering_the_economics_of_photovoltaic_power_a_co_authored_white.pdf | title = Re-considering the economics of photovoltaic power | journal = Renewable Energy | volume = 53 | pages = 329–338 | year = 2013 | last1 = Bazilian | first1 = M. | last2 = Onyeji | first2 = I. | last3 = Liebreich | first3 = M. | last4 = MacGill | first4 = I. | last5 = Chase | first5 = J. | last6 = Shah | first6 = J. | last7 = Gielen | first7 = D. | last8 = Arent | first8 = D. | last9 = Landfear | first9 = D. | last10 = Zhengrong | first10 = S. | citeseerx = 10.1.1.692.1880 | access-date = 4 September 2015 | archive-url = https://web.archive.org/web/20140531105637/http://az2112.com/assets/energy-bnef_re_considering_the_economics_of_photovoltaic_power_a_co_authored_white.pdf | archive-date = 31 May 2014  }}</ref> The average retail price of solar cells as monitored by the Solarbuzz group fell from $3.50/watt to $2.43/watt over the course of 2011.<ref name=natint /> In 2013 wholesale prices had fallen to $0.74/W.<ref name="Econ1"/> This has been cited as evidence supporting '[[Swanson's law]]', an observation similar to the famous Moore's Law, which claims that solar cell prices fall 20% for every doubling of industry capacity.<ref name="Econ1" /> The Fraunhofer Institute defines the 'learning rate' as the drop in prices as the cumulative production doubles, some 25% between 1980 and 2010. Although the prices for modules have dropped quickly, current inverter prices have dropped at a much lower rate, and in 2019 constitute over 61% of the cost per kWp, from a quarter in the early 2000s.<ref name="fraunhofer-pv-report-2020-p36"/>

Note that the prices mentioned above are for bare modules, another way of looking at module prices is to include installation costs. In the US, according to the Solar Energy Industries Association, the price of installed rooftop PV modules for homeowners fell from $9.00/W in 2006 to $5.46/W in 2011. Including the prices paid by industrial installations, the national installed price drops to $3.45/W. This is markedly higher than elsewhere in the world, in Germany homeowner rooftop installations averaged at $2.24/W. The cost differences are thought to be primarily based on the higher regulatory burden and lack of a national solar policy in the US.<ref name=wells2012>{{cite news|author=Wells, Ken|date=25 October 2012 |title=Solar Energy Is Ready. The U.S. Isn't |magazine=Bloomberg Businessweek |url=http://www.businessweek.com/articles/2012-10-25/solar-energy-is-ready-dot-the-u-dot-s-dot-isnt |archive-url=https://web.archive.org/web/20121027031637/http://www.businessweek.com/articles/2012-10-25/solar-energy-is-ready-dot-the-u-dot-s-dot-isnt  |archive-date=27 October 2012 |access-date=1 November 2012}}</ref>

By the end of 2012 Chinese manufacturers had production costs of $0.50/W in the cheapest modules.<ref>[http://www.greentechmedia.com/articles/read/solar-pv-module-costs-to-fall-to-36-cents-per-watt Solar PV Module Costs to Fall to 36 Cents per Watt by 2017]. Greentechmedia.com (2013-06-18). Retrieved on 2015-04-15.</ref> In some markets distributors of these modules can earn a considerable margin, buying at factory-gate price and selling at the highest price the market can support ('value-based pricing').<ref name=reconsidering/>

In California PV reached grid parity in 2011, which is usually defined as PV production costs at or below retail electricity prices (though often still above the power station prices for coal or gas-fired generation without their distribution and other costs).<ref name=Alafita2014>{{Cite journal | doi = 10.1016/j.enpol.2013.12.045| title = Securitization of residential solar photovoltaic assets: Costs, risks and uncertainty| journal = Energy Policy| volume = 67| pages = 488–498| year = 2014| last1 = Alafita | first1 = T.| last2 = Pearce | first2 = J. M. | s2cid = 11079398| url = https://digitalcommons.mtu.edu/cgi/viewcontent.cgi?article=1022&context=materials_fp}}</ref> Grid parity had been reached in 19 markets in 2014.<ref name=bloomberg-leibreich-2014>{{cite web|last1=Liebreich|first1=Michael|title=A YEAR OF CRACKING ICE: 10 PREDICTIONS FOR 2014|url=http://about.bnef.com/blog/liebreich-a-year-of-cracking-ice-10-predictions-for-2014/|publisher=Bloomberg New Energy Finance|access-date=24 April 2014|date=29 January 2014}}</ref><ref>{{cite web |title= 2014 Outlook: Let the Second Gold Rush Begin |url=https://www.deutschebank.nl/nl/docs/Solar_-_2014_Outlook_Let_the_Second_Gold_Rush_Begin.pdf?dbiquery=null%3Avishal+shah |publisher=Deutsche Bank Markets Research |date=6 January 2014 |access-date=22 November 2014 |archive-date=29 November 2014 |archive-url=https://web.archive.org/web/20141129041750/https://www.deutschebank.nl/nl/docs/Solar_-_2014_Outlook_Let_the_Second_Gold_Rush_Begin.pdf?dbiquery=null%3Avishal+shah |url-status=live }}</ref>

===Levelised cost of electricity===
[[File:AWM-Munich-ETFE-Cushions-Photovoltaic.jpg|thumb|upright=1.2|AWM Munich [[Chemistry:ETFE|ETFE]] Cushions-Photovoltaics]]
The levelised cost of electricity (LCOE) is the cost per kWh based on the costs distributed over the project lifetime, and is thought to be a better metric for calculating viability than price per wattage. LCOEs vary dramatically depending on the location.<ref name=reconsidering/> The LCOE can be considered the minimum price customers will have to pay the utility company in order for it to break even on the investment in a new power station.<ref name="our-world-in-data-pv-2020"/> Grid parity is roughly achieved when the LCOE falls to a similar price as conventional local grid prices, although in actuality the calculations are not directly comparable.<ref name="Branker">{{cite journal|doi=10.1016/j.rser.2011.07.104 |title=A Review of Solar Photovoltaic Levelized Cost of Electricity |year=2011 |last1=Branker |first1=K. |last2=Pathak |first2=M.J.M. |last3=Pearce |first3=J.M. |journal=Renewable and Sustainable Energy Reviews |volume=15 |issue=9 |pages=4470–4482 |hdl=1974/6879|s2cid=73523633 |url=https://digitalcommons.mtu.edu/cgi/viewcontent.cgi?article=1028&context=materials_fp |hdl-access=free }}</ref> Large industrial PV installations had reached grid parity in California in 2011.<ref name=SilverLining/><ref name="Branker"/> Grid parity for rooftop systems was still believed to be much farther away at this time.<ref name="Branker"/> Many LCOE calculations are not thought to be accurate, and a large amount of assumptions are required.<ref name=reconsidering/><ref name="Branker"/> Module prices may drop further, and the LCOE for solar may correspondingly drop in the future.<ref name=invest2011>{{cite web |url=http://www.renewableenergyworld.com/rea/news/article/2011/08/renewables-investment-breaks-records |title=Renewables Investment Breaks Records|date=29 August 2011 |website=Renewable Energy World }}</ref>

Because energy demands rise and fall over the course of the day, and solar power is limited by the fact that the sun sets, solar power companies must also factor in the additional costs of supplying a more stable alternative energy supplies to the grid in order to stabilize the system, or storing the energy somehow (current battery technology cannot store enough power). These costs are not factored into LCOE calculations, nor are special subsidies or premiums that may make buying solar power more attractive.<ref name="our-world-in-data-pv-2020"/> The unreliability and temporal variation in generation of solar and wind power is a major problem. Too much of these volatile power sources can cause instability of the entire grid.<ref>{{cite news |last=Hockenos |first=Paul |date=10 February 2021 |title=Is Germany Making Too Much Renewable Energy? |url=https://foreignpolicy.com/2021/02/10/is-germany-making-too-much-renewable-energy/ |work=Foreign Policy |access-date=7 March 2021}}</ref>

As of 2017 power-purchase agreement prices for solar farms below $0.05/kWh are common in the United States, and the lowest bids in some Persian Gulf countries were about $0.03/kWh.<ref name="Haegel 2017">{{cite journal  | author = Nancy M. Haegel | title = Terawatt-scale photovoltaics: Trajectories and challenges  | journal =Science | volume = 356 |issue = 6334 | pages = 141–143  | date = 2017 | doi =10.1126/science.aal1288 | pmid = 28408563  | bibcode = 2017Sci...356..141H| hdl = 10945/57762  | osti = 1352502 | s2cid = 206654326 }}</ref> The goal of the United States Department of Energy is to achieve a levelised cost of energy for solar PV of $0.03/kWh for utility companies.<ref name=Adeh2019>{{Cite journal|last1=Adeh|first1=Elnaz H.|last2=Good|first2=Stephen P.|last3=Calaf|first3=M.|last4=Higgins|first4=Chad W.|date=2019-08-07|title=Solar PV Power Potential is Greatest Over Croplands|journal=Scientific Reports|language=en|volume=9|issue=1|page=11442|doi=10.1038/s41598-019-47803-3|pmid=31391497|pmc=6685942|bibcode=2019NatSR...911442A|issn=2045-2322|doi-access=free}}</ref>

===Subsidies and financing===
[[Physics:Financial incentives for photovoltaics|Financial incentives for photovoltaics]], such as feed-in tariffs (FITs), have often been offered to electricity consumers to install and operate solar-electric generating systems, and in some countries such subsidies are the only way photovoltaics can remain economically profitable. In Germany FIT subsidies are generally around €0.13 above the normal retail price of a kWh (€0.05).<ref name=TROMMSDORFF>{{Cite journal|last=TROMMSDORFF|first=Maximillian|date=2016|title=An economic analysis of agrophotovoltaics: Opportunities, risks and strategies towards a more efficient land use|url=https://www.econstor.eu/bitstream/10419/150976/1/879248831.pdf|journal=The Constitutional Economics Network Working Papers}}</ref> PV FITs have been crucial for the adoption of the industry, and are available to consumers in over 50 countries as of 2011. Germany and Spain have been the most important countries regarding offering subsidies for PV, and the policies of these countries have driven demand in the past.<ref name=reconsidering /> Some US solar cell manufacturing companies have repeatedly complained that the dropping prices of PV module costs have been achieved due to subsidies by the government of China, and the dumping of these products below fair market prices. US manufacturers generally recommend high tariffs on foreign supplies to allow them remain profitable. In response to these concerns, the Obama administration began to levy tariffs on US consumers of these products in 2012 to raise prices for domestic manufacturers.<ref name=reconsidering /> The USA, however, also subsidies the industry, offering consumers a 30% federal tax credit to purchase modules. In Hawaii federal and state subsidies chop off up to two thirds of the installation costs.<ref name=wells2012/>

Some environmentalists have promoted the idea that government incentives should be used in order to expand the PV manufacturing industry to reduce costs of PV-generated electricity much more rapidly to a level where it is able to compete with fossil fuels in a free market. This is based on the theory that when the manufacturing capacity doubles, [[Finance:Economies of scale|economies of scale]] will cause the prices of the solar products to halve.<ref name="our-world-in-data-pv-2020"/>

In many countries there is access to capital is lacking to develop PV projects. To solve this problem, [[Finance:Securitization|securitization]] has been proposed to accelerate development of solar photovoltaic projects.<ref name=Alafita2014/><ref>Lowder, T., & Mendelsohn, M. (2013). ''The Potential of Securitization in Solar PV Finance''.{{page needed|date=February 2017}}</ref> For example, SolarCity offered the first U.S. [[Finance:Asset-backed security|asset-backed security]] in the solar industry in 2013.<ref>[https://www.forbes.com/sites/uciliawang/2013/11/21/done-deal-the-first-securitization-of-rooftop-solar-assets/ "Done Deal: The First Securitization Of Rooftop Solar Assets"]. ''Forbes''. 21 November 2013</ref>

===Other===
Photovoltaic power is also generated during a time of day that is close to peak demand (precedes it) in electricity systems with high use of air conditioning. Since large-scale PV operation requires back-up in the form of spinning reserves, its marginal cost of generation in the middle of the day is typically lowest, but not zero, when PV is generating electricity. This can be seen in Figure 1 of this paper:.<ref>{{cite journal |doi=10.1016/j.enpol.2017.07.060 |title=Jointly reforming the prices of industrial fuels and residential electricity in Saudi Arabia |journal=Energy Policy |volume=109 |pages=747–756 |year=2017 |last1=Matar |first1=Walid |last2=Anwer |first2=Murad|doi-access=free }}</ref> For residential properties with private PV facilities networked to the grid, the owner may be able earn extra money when the time of generation is included, as electricity is worth more during the day than at night.<ref>[http://www.greentechmedia.com/articles/read/Utilities-Honest-Assessment-of-Solar-in-the-Electricity-Supply/ Utilities' Honest Assessment of Solar in the Electricity Supply]. Greentechmedia.com (7 May 2012). Retrieved on 31 May 2013.</ref>

One journalist theorised in 2012 that if the energy bills of Americans were forced upwards by imposing an extra tax of $50/ton on carbon dioxide emissions from coal-fired power, this could have allowed solar PV to appear more cost-competitive to consumers in most locations.<ref name=natint>{{cite web |url=http://nationalinterest.org/commentary/the-end-the-nuclear-renaissance-6325?page=1 |title=The End of the Nuclear Renaissance|author=Quiggin, John|date=3 January 2012|website=National Interest}}</ref>

== Growth ==
{{Main|Physics:Growth of photovoltaics}}
[[File:PV cume semi log chart 2014 estimate.svg|thumb|upright=1.2|Worldwide growth of photovoltaics on a semi-log plot since 1992]]

Solar photovoltaics formed the largest body of research among the seven sustainable energy types examined in a global bibliometric study, with the annual scientific output growing from 9,094 publications in 2011 to 14,447 publications in 2019.<ref name="Straza & Schneegans 2021">{{cite book |author1=Straza |author2=Schneegans |title=Are we using science for smarter development? |date=11 June 2021 |publisher=UNESCO |location=Paris |isbn=978-92-3-100450-6 |url=https://unesdoc.unesco.org/ark:/48223/pf0000377454/PDF/377454eng.pdf.multi}}</ref>

Likewise, the application of solar photovoltaics is growing rapidly and the worldwide installed capacity reached one terawatt in April 2022.<ref name="IEA-PVPS-2016">{{cite web |url=http://www.iea-pvps.org/fileadmin/dam/public/report/statistics/IEA-PVPS_-_A_Snapshot_of_Global_PV_-_1992-2016__1_.pdf|title=Snapshot of Global Photovoltaic Markets 2017|date=19 April 2017 |access-date=11 July 2017 |website=report |publisher=International Energy Agency}}</ref> The total power output of the world's PV capacity in a calendar year is now beyond 500 TWh of electricity. This represents 2% of worldwide electricity demand. More than 100 countries, such as Brazil and India, use solar PV.<ref name="iea-pvps-snapshot-1992-2014">{{cite web |url=http://www.iea-pvps.org/fileadmin/dam/public/report/technical/PVPS_report_-_A_Snapshot_of_Global_PV_-_1992-2014.pdf |title=Snapshot of Global PV 1992–2014 |publisher=International Energy Agency — Photovoltaic Power Systems Programme |date=30 March 2015 |archive-url=https://web.archive.org/web/20150407023056/http://www.iea-pvps.org/index.php?id=92&eID=dam_frontend_push&docID=2430 |archive-date=7 April 2015 |url-status=live
}}</ref><ref name="ren21-2011">{{cite web |url=http://www.ren21.net/REN21Activities/GlobalStatusReport.aspx |title=Renewables 2011: Global Status Report |publisher=[[Organization:REN21|REN21]] |year=2011 |page=22 |access-date=31 May 2013 |archive-date=13 September 2014 |archive-url=https://web.archive.org/web/20140913111511/http://www.ren21.net/ren21activities/globalstatusreport.aspx |url-status=dead }}</ref> China is followed by the United States and Japan, while installations in Germany, once the world's largest producer, have been slowing down.

Honduras generated the highest percentage of its energy from solar in 2019, 14.8%.<ref>{{Cite web|url=https://iea-pvps.org/snapshot-reports/snapshot-2020/|title=Snapshot 2020|website=IEA-PVPS}}</ref> As of 2019, Vietnam has the highest installed capacity in Southeast Asia, about 4.5 GW.<ref name=":11">{{Cite journal|last1=Do|first1=Thang Nam|last2=Burke|first2=Paul J.|last3=Baldwin|first3=Kenneth G. H.|last4=Nguyen|first4=Chinh The|date=2020-09-01|title=Underlying drivers and barriers for solar photovoltaics diffusion: The case of Vietnam|url=http://www.sciencedirect.com/science/article/pii/S0301421520303037|journal=Energy Policy|language=en|volume=144|page=111561|doi=10.1016/j.enpol.2020.111561|issn=0301-4215|hdl=1885/206307|s2cid=225245522|hdl-access=free}}</ref> The annualized installation rate of about 90&nbsp;W per capita per annum places Vietnam among world leaders.<ref name=":11" /> Generous Feed-in tariff (FIT) and government supporting policies such as tax exemptions were the key to enable Vietnam's solar PV boom. Underlying drivers include the government's desire to enhance energy self-sufficiency and the public's demand for local environmental quality.<ref name=":11" />

A key barrier is limited transmission grid capacity.<ref name=":11" />

China has the world's largest solar power capacity, with 390&nbsp;GW of installed capacity in 2022 compared with about 200&nbsp;GW in the European Union, according to International Energy Agency data.<ref>{{Cite news |date=2021-07-23 |title=China to add 55-65 GW of solar power capacity in 2021 -industry body |language=en |work=Reuters |url=https://www.reuters.com/business/energy/china-add-55-65-gw-solar-power-capacity-2021-industry-body-2021-07-22/ |access-date=2022-10-15}}</ref> Other countries with the world's largest solar power capacities include the United States, Japan and Germany.

<!-- wrapper for top20 tables -->
{{anchor|Top 20 ranking of worldwide photovoltaic installation}}
{| style="max-width: 600px; margin: 1px auto;"
|+ '''Top 20 PV countries in 2022 (MW)'''
|- style="background-color: none;"
| align=center |<!-- top ten countries of current year -->
<!-- DETAIL TABLE: Installed solar power capacity (by country) -->
{| class="wikitable sortable" style="text-align:right; margin: 18px auto 1px auto;"
|+ Installed and total solar power capacity in 2022 (MW)<ref name="iea-pvps-snapshot-2020">{{cite web |title=Snapshot 2020 – IEA-PVPS |url=https://iea-pvps.org/snapshot-reports/snapshot-2020/ |website=iea-pvps.org |access-date=10 May 2020}}</ref>
|-
! style="background-color:#cfb"|# !! style="background-color:#cfb"|Nation !! style="background-color:#cfb" data-sort-type="number"|Total capacity !! style="background-color:#cfb" data-sort-type="number" |Added capacity
|-
| 1 || align=left|{{flagicon|CHN}} China || 393,000 || 86,100
|-
| 2 || align=left|{{flagicon|USA}} United States || 113,000 || 17,800
|-
| 3 || align=left|{{flagicon|JPN}} Japan || 78,800 || 4,600
|-
| 4 || align=left|{{flagicon|GER}} Germany || 66,600 || 8,100
|-
| 5 || align=left|{{flagicon|India}} India || 63,100 || 13,500
|-
| 6 || align=left|{{flagicon|Australia}} [[Engineering:Solar power in Australia|Australia]] || 26,800 || 7,700
|-
| 7 || align=left|{{flagicon|Italy}} Italy || 25,100 || 2,400
|-
| 8 || align=left|{{flagicon|Brazil}} Brazil || 24,100 || 9,900
|-
| 9 || align=left|{{flagicon|South Korea}} South Korea || 21,000 || 2,800
|-
| 10 || align=left|{{flagicon|Spain}} Spain || 20,500 || 4,600
|-
| 11 || align=left|{{flagicon|Netherlands}} Netherlands || 19,100 || 4,200
|-
| 12 || align=left|{{flagicon|Vietnam}} Vietnam || 18,500 || 1,800
|-
| 13 || align=left|{{flagicon|France}} France || 17,400 || 2,700
|-
| 14 || align=left|{{flagicon|UK}} United Kingdom || 14,400 || 720
|-
| 15 || align=left|{{flagicon|Poland}} Poland || 11,200 || 4,900
|-
| 16 || align=left|{{flagicon|Taiwan}} Taiwan || 9,700 || 2,000
|-
| 17 || align=left|{{flagicon|Turkey}} Turkey || 9,400 || 1,600
|-
| 18 || align=left|{{flagicon|Mexico}} Mexico || 9,000 || 2,000
|-
| 19 || align=left|{{flagicon|Ukraine}} Ukraine || 8,100 || 0
|-
| 20 || align=left|{{flagicon|Belgium}} Belgium || 6,900 || 310
|-
|}
<!-- footer -->
|-
| colspan=3 style="font-size: 85%; padding: 5px 0 0 20px;"|
Data: [[Organization:International Energy Agency#Promotion of renewable energy – Photovoltaic Power Systems Programme|IEA-PVPS]] ''Snapshot of Global PV Markets 2023'' report, April 2023<ref name="iea-pvps-snapshot-2020"/><br />''Also see Solar power by country for a complete and continuously updated list''
<!-- end wrapper of top20 tables -->
|}

In 2017, it was thought probable that by 2030 global PV installed capacities could be between 3,000 and 10,000&nbsp;GW.<ref name="Haegel 2017" /> Greenpeace in 2010 claimed that 1,845&nbsp;GW of PV systems worldwide could be generating approximately 2,646&nbsp;TWh/year of electricity by 2030, and by 2050 over 20% of all electricity could be provided by PV.<ref name=epia>[http://www.epia.org/publications/epiapublications/solar-generation-6.html Solar Photovoltaic Electricity Empowering the World] {{webarchive|url=https://web.archive.org/web/20120822034710/http://www.epia.org/publications/epiapublications/solar-generation-6.html |date=22 August 2012 }}. Epia.org (22 September 2012). Retrieved on 31 May 2013.</ref>

== Applications ==

There are many practical applications for the use of solar panels or photovoltaics covering every technological domain under the sun. From the fields of the agricultural industry as a power source for irrigation to its usage in remote health care facilities to refrigerate medical supplies. Other applications include power generation at various scales and attempts to integrate them into homes and public infrastructure. PV modules are used in photovoltaic systems and include a large variety of electrical devices.

=== Photovoltaic systems ===
{{Main|Physics:Photovoltaic system}}

A photovoltaic system, or solar PV system is a power system designed to supply usable solar power by means of photovoltaics. It consists of an arrangement of several components, including solar panels to absorb and directly convert sunlight into electricity, a solar inverter to change the electric current from DC to AC, as well as mounting, cabling and other electrical accessories. PV systems range from small, [[Physics:Rooftop photovoltaic power station|roof-top mounted]] or building-integrated systems with capacities from a few to several tens of kilowatts, to large utility-scale [[Physics:Photovoltaic power station|power stations]] of hundreds of megawatts. Nowadays, most PV systems are [[Physics:Grid-connected photovoltaic power system|grid-connected]], while [[Engineering:Stand-alone power system|stand-alone]] systems only account for a small portion of the market.

===Photo sensors===
Photosensors are sensors of [[Physics:Light|light]] or other [[Physics:Electromagnetic radiation|electromagnetic radiation]].<ref>{{cite journal|doi=10.1063/1.2884264|title=Study of residual background carriers in midinfrared InAs/GaSb superlattices for uncooled detector operation|year=2008|last1=Haugan|first1=H. J.|last2=Elhamri|first2=S.|last3=Szmulowicz|first3=F.|last4=Ullrich|first4=B.|last5=Brown|first5=G. J.|last6=Mitchel|first6=W. C.|journal=Applied Physics Letters|volume=92|issue=7|page=071102|bibcode = 2008ApPhL..92g1102H |s2cid=39187771}}</ref>  A photo detector has a [[Physics:P–n junction|p–n junction]] that converts light photons into current. The absorbed photons make electron–hole pairs in the [[Physics:Depletion region|depletion region]]. [[Physics:Photodiode|Photodiode]]s and photo transistors are a few examples of photo detectors.  [[Physics:Solar cell|Solar cell]]s convert some of the light energy absorbed into electrical energy.

== Experimental technology ==

Crystalline silicon photovoltaics are only one type of PV, and while they represent the majority of solar cells produced currently there are many new and promising technologies that have the potential to be scaled up to meet future energy needs. As of 2018, crystalline silicon cell technology serves as the basis for several PV module types, including monocrystalline, multicrystalline, mono PERC, and bifacial.<ref>{{cite web|title = Solar PV Modules |url = https://www.targray.com/solar/pv-modules|website = www.targray.com|access-date = 2018-10-03}}</ref>

Another newer technology, thin-film PV, are manufactured by depositing semiconducting layers of [[Chemistry:Perovskite|perovskite]], a mineral with semiconductor properties, on a substrate in vacuum. The substrate is often glass or stainless-steel, and these semiconducting layers are made of many types of materials including [[Chemistry:Cadmium telluride|cadmium telluride]] (CdTe), copper indium diselenide (CIS), copper indium gallium diselenide (CIGS), and amorphous silicon (a-Si). After being deposited onto the substrate the semiconducting layers are separated and connected by electrical circuit by laser scribing.<ref>{{cite journal |last1=Kosasih |first1=Felix Utama |last2=Rakocevic |first2=Lucija |last3=Aernouts |first3=Tom |last4=Poortmans |first4=Jef |last5=Ducati |first5=Caterina |title=Electron Microscopy Characterization of P3 Lines and Laser Scribing-Induced Perovskite Decomposition in Perovskite Solar Modules |journal=ACS Applied Materials & Interfaces |date=11 December 2019 |volume=11 |issue=49 |pages=45646–45655 |doi=10.1021/acsami.9b15520|pmid=31663326 |s2cid=204967452 |url=https://www.repository.cam.ac.uk/handle/1810/298307 }}</ref><ref>{{cite journal |last1=Di Giacomo |first1=Francesco |last2=Castriotta |first2=Luigi A. |last3=Kosasih |first3=Felix U. |last4=Di Girolamo |first4=Diego |last5=Ducati |first5=Caterina |last6=Di Carlo |first6=Aldo |title=Upscaling Inverted Perovskite Solar Cells: Optimization of Laser Scribing for Highly Efficient Mini-Modules |journal=Micromachines |date=20 December 2020 |volume=11 |issue=12 |page=1127 |doi=10.3390/mi11121127|pmid=33419276 |pmc=7767295 |doi-access=free }}</ref> Perovskite solar cells are a very efficient solar energy converter and have excellent optoelectronic properties for photovoltaic purposes, but their upscaling from lab-sized cells to large-area modules is still under research.<ref name=Matteocci2019>{{cite journal |last1=Matteocci |first1=Fabio |last2=Vesce |first2=Luigi |last3=Kosasih |first3=Felix Utama |last4=Castriotta |first4=Luigi Angelo |last5=Cacovich |first5=Stefania |last6=Palma |first6=Alessandro Lorenzo |last7=Divitini |first7=Giorgio |last8=Ducati |first8=Caterina |last9=Di Carlo |first9=Aldo |title=Fabrication and Morphological Characterization of High-Efficiency Blade-Coated Perovskite Solar Modules |journal=ACS Applied Materials & Interfaces |date=17 July 2019 |volume=11 |issue=28 |pages=25195–25204 |doi=10.1021/acsami.9b05730|pmid=31268662 |s2cid=206497286 |url=https://www.repository.cam.ac.uk/handle/1810/294343 }}</ref> Thin-film photovoltaic materials may possibly become attractive in the future, because of the reduced materials requirements and cost to manufacture modules consisting of thin-films as compared to silicon-based wafers.<ref>{{cite web|title = Thin Film Photovoltaics|url = http://www.fsec.ucf.edu/en/consumer/solar_electricity/basics/thin-film.htm|website = www.fsec.ucf.edu|access-date = 2015-11-05}}</ref> In 2019 university labs at Oxford, Stanford and elsewhere reported perovskite solar cells with efficiencies of 20-25%.<ref name="NREL">[https://www.nrel.gov/pv/cell-efficiency.html Best Research Cell Efficiences]. nrel.gov (16 September 2019). Retrieved on 31 October 2019.</ref>

=== CIGS ===

{{Main|Chemistry:Copper indium gallium selenide}}

Copper indium gallium selenide (CIGS) is a thin film solar cell based on the copper indium diselenide (CIS) family of chalcopyrite [[Physics:Semiconductor|semiconductor]]s. CIS and CIGS are often used interchangeably within the CIS/CIGS community. The cell structure includes soda lime glass as the substrate, Mo layer as the back contact, CIS/CIGS as the absorber layer, cadmium sulfide (CdS) or Zn (S,OH)x as the buffer layer, and ZnO:Al as the front contact.<ref>{{cite journal|author=Eisenberg, D. A., Yu, M., Lam, C. W., Ogunseitan, O. A. & Schoenung, J. M. |title=Comparative alternative materials assessment to screen toxicity hazards in the life cycle of CIGS thin film photovoltaics|journal= Journal of Hazardous Materials |volume=260|pages= 534–542 |year=2013|pmid=23811631|doi=10.1016/j.jhazmat.2013.06.007|s2cid=26540719 |url=http://www.escholarship.org/uc/item/1jv7f94k}}</ref> CIGS is approximately 1/100th the thickness of conventional silicon solar cell technologies. Materials necessary for assembly are readily available, and are less costly per watt of solar cell. CIGS based solar devices resist performance degradation over time and are highly stable in the field.

Reported global warming potential impacts of CIGS ranges 20.5–58.8 grams CO<sub>2</sub>-eq/kWh of electricity generated for different solar irradiation (1,700 to 2,200&nbsp;kWh/m<sup>2</sup>/y) and power conversion efficiency (7.8 – 9.12%).<ref>{{cite journal|doi=10.1111/j.1530-9290.2011.00423.x|author=Kim, H. C., Fthenakis, V., Choi, J. K. & Turney, D. E. |title=Life cycle greenhouse gas emissions of thin-film photovoltaic electricity generation|journal= Journal of Industrial Ecology |volume=16|pages= S110–S121 |year=2012|s2cid=153386434 |doi-access=free}}</ref> EPBT ranges from 0.2 to 1.4 years,<ref name=":8" /> while harmonized value of EPBT was found 1.393 years.<ref name=":3" /> Toxicity is an issue within the buffer layer of CIGS modules because it contains cadmium and gallium.<ref name=":2" /><ref>{{cite conference |last1=Werner |first1=Jürgen H. |last2=Zapf-Gottwick |first2=R. |last3=Koch |first3=M. |last4=Fischer |first4=K. |title=Toxic substances in photovoltaic modules |conference=Proceedings of the 21st International Photovoltaic Science and Engineering Conference |location=Fukuoka, Japan |volume=28 |year=2011 }}</ref> CIS modules do not contain any heavy metals.

=== Perovskite solar cells ===
{{Excerpt|Perovskite solar cell}}

=== Dye-Sensitized Solar Cells ===

[[Physics:Dye-sensitized solar cell|Dye-sensitized solar cell]]s (DSCs) are a novel thin film solar cell. These solar cells operate under ambient light better than other photovoltaic technologies. They work with light being absorbed in a sensitizing dye between two charge transport materials. Dye surrounds TiO<sub>2</sub> [[Physics:Nanoparticle|nanoparticle]]s which are in a sintered network.<ref>{{Cite journal |last=Goodson |first=Flynt |date=2014 |title=Supramolecular Multichromophoric Dye Sensitized Solar Cells |url=https://diginole.lib.fsu.edu/islandora/object/fsu%3A254429/datastream/PDF/view |url-status=live |archive-url=https://web.archive.org/web/20221209191458/https://diginole.lib.fsu.edu/islandora/object/fsu%3A254429/datastream/PDF/view |archive-date=2022-12-09}}</ref> TiO<sub>2</sub> acts as conduction band in an n-type semiconductor; the scaffold for adorned dye molecules and transports elections during excitation. For TiO<sub>2</sub> DSC technology, sample preparation at high temperatures is very effective because higher temperatures produce more suitable textural properties.  Another example of DSCs is the copper complex with Cu (II/I) as a redox shuttle with TMBY (4,4',6,6'-tetramethyl-2,2'bipyridine). DSCs show great performance with artificial and indoor light. From a range of 200 lux to 2,000 lux, these cells operate at conditions of a maximum efficiency of 29.7%.<ref>{{Cite journal|url=https://www.nature.com/articles/nphoton.2017.60|title=Dye-sensitized solar cells for efficient power generation under ambient lighting|first1=Marina|last1=Freitag|first2=Joël|last2=Teuscher|first3=Yasemin|last3=Saygili|first4=Xiaoyu|last4=Zhang|first5=Fabrizio|last5=Giordano|first6=Paul|last6=Liska|first7=Jianli|last7=Hua|first8=Shaik M.|last8=Zakeeruddin|first9=Jacques-E.|last9=Moser|first10=Michael|last10=Grätzel|first11=Anders|last11=Hagfeldt|date=17 June 2017|journal=Nature Photonics|volume=11|issue=6|pages=372–378|via=www.nature.com|doi=10.1038/nphoton.2017.60|bibcode=2017NaPho..11..372F |s2cid=10780585 }}</ref>

However, there have been issues with DSCs, many of which come from the liquid electrolyte. The solvent is hazardous, and will permeate most plastics. Because it is liquid, it is unstable to temperature variation, leading to freezing in cold temperatures and expansion in warm temperatures causing failure.<ref>{{Cite journal|url=https://pubs.rsc.org/en/content/articlelanding/2013/cp/c2cp43220j|title=Temperature effects in dye-sensitized solar cells|first1=Sonia R.|last1=Raga|first2=Francisco|last2=Fabregat-Santiago|date=23 January 2013|journal=Physical Chemistry Chemical Physics|volume=15|issue=7|pages=2328–2336|via=pubs.rsc.org|doi=10.1039/C2CP43220J|pmid=23295858 |bibcode=2013PCCP...15.2328R }}</ref> Another disadvantage is that the solar cell is not ideal for large scale application because of its low efficiency. Some of the benefits for DSC is that it can be used in a variety of light levels (including cloudy conditions), it has a low production cost, and it does not degrade under sunlight, giving it a longer lifetime then other types of thin film solar cells.

=== OPV ===

Other possible future PV technologies include organic, dye-sensitized and quantum-dot photovoltaics.<ref>{{cite journal |last1=Nikolaidou |first1=Katerina |last2=Sarang |first2=Som|last3=Ghosh |first3=Sayantani|title= Nanostructured photovoltaics |journal=Nano Futures |volume =3 |issue= 1|page =012002 | year=2019|doi=10.1088/2399-1984/ab02b5 |bibcode=2019NanoF...3a2002N |s2cid=162176556 }}</ref> Organic photovoltaics (OPVs) fall into the thin-film category of manufacturing, and typically operate around the 12% efficiency range which is lower than the 12–21% typically seen by silicon-based PVs. Because organic photovoltaics require very high purity and are relatively reactive they must be encapsulated which vastly increases the cost of manufacturing and means that they are not feasible for large scale-up. Dye-sensitized PVs are similar in efficiency to OPVs but are significantly easier to manufacture. However, these dye-sensitized photovoltaics present storage problems because the liquid electrolyte is toxic and can potentially permeate the plastics used in the cell. Quantum dot solar cells are solution-processed, meaning they are potentially scalable, but currently they peak at 12% efficiency.<ref name=Matteocci2019/>

[[Physics:Organic solar cell|Organic]] and polymer photovoltaic (OPV) are a relatively new area of research. The tradition OPV cell structure layers consist of a semi-transparent electrode, electron blocking layer, tunnel junction, holes blocking layer, electrode, with the sun hitting the transparent electrode. OPV replaces silver with carbon as an electrode material lowering manufacturing cost and making them more environmentally friendly.<ref>{{cite journal|doi=10.1002/aenm.201400732|title=Carbon: The Ultimate Electrode Choice for Widely Distributed Polymer Solar Cells|journal=Advanced Energy Materials|volume=4|issue=15|pages=n/a|year=2014|last1=Dos Reis Benatto|first1=Gisele A.|last2=Roth|first2=Bérenger|last3=Madsen|first3=Morten V.|last4=Hösel|first4=Markus|last5=Søndergaard|first5=Roar R.|last6=Jørgensen|first6=Mikkel|last7=Krebs|first7=Frederik C.|s2cid=96990654}}</ref> OPV are flexible, low weight, and work well with roll-to roll manufacturing for mass production.<ref>{{cite journal|doi=10.3390/electronics3010132 |title=Electron and Hole Transport Layers: Their Use in Inverted Bulk Heterojunction Polymer Solar Cells |journal=Electronics |volume=3 |pages=132–164 |year=2014 |last1=Lattante |first1=Sandro |doi-access=free }}</ref> OPV uses "only abundant elements coupled to an extremely low embodied energy through very low processing temperatures using only ambient processing conditions on simple printing equipment enabling energy pay-back times".<ref name=":1">{{cite journal|doi=10.1016/j.solmat.2013.05.032|title=Polymer and organic solar cells viewed as thin film technologies: What it will take for them to become a success outside academia|journal=Solar Energy Materials and Solar Cells|volume=119|pages=73–76|year=2013|last1=Krebs|first1=Frederik C.|last2=Jørgensen|first2=Mikkel}}</ref> Current efficiencies range 1–6.5%,<ref name=":0" /><ref>{{cite journal|doi=10.1016/j.solmat.2010.08.020|title=A life cycle analysis of polymer solar cell modules prepared using roll-to-roll methods under ambient conditions|journal=Solar Energy Materials and Solar Cells|volume=95|issue=5|pages=1293–1302|year=2011|last1=Espinosa|first1=Nieves|last2=García-Valverde|first2=Rafael|last3=Urbina|first3=Antonio|last4=Krebs|first4=Frederik C.}}</ref> however theoretical analyses show promise beyond 10% efficiency.<ref name=":1" />

Many different configurations of OPV exist using different materials for each layer. OPV technology rivals existing PV technologies in terms of EPBT even if they currently present a shorter operational lifetime. A 2013 study analyzed 12 different configurations all with 2% efficiency, the EPBT ranged from 0.29 to 0.52 years for 1&nbsp;m<sup>2</sup> of PV.<ref>{{cite journal|doi=10.1039/C3TA01611K |title=OPV for mobile applications: An evaluation of roll-to-roll processed indium and silver free polymer solar cells through analysis of life cycle, cost and layer quality using inline optical and functional inspection tools |journal=Journal of Materials Chemistry A |volume=1 |issue=24 |page=7037 |year=2013 |last1=Espinosa |first1=Nieves |last2=Lenzmann |first2=Frank O. |last3=Ryley |first3=Stephen |last4=Angmo |first4=Dechan |last5=Hösel |first5=Markus |last6=Søndergaard |first6=Roar R. |last7=Huss |first7=Dennis |last8=Dafinger |first8=Simone |last9=Gritsch |first9=Stefan |last10=Kroon |first10=Jan M. |last11=Jørgensen |first11=Mikkel |last12=Krebs |first12=Frederik C. |url=http://resolver.tudelft.nl/uuid:4edf52d6-7387-460f-adea-d2a484a4992b }}</ref> The average CO<sub>2</sub>-eq/kWh for OPV is 54.922 grams.<ref>{{cite journal|doi=10.1016/j.solener.2009.03.012|title=Life cycle assessment study of a 4.2k ''Wp'' stand-alone photovoltaic system|journal=Solar Energy|volume=83|issue=9|pages=1434–1445|year=2009|last1=García-Valverde|first1=R.|last2=Miguel|first2=C.|last3=Martínez-Béjar|first3=R.|last4=Urbina|first4=A.|bibcode=2009SoEn...83.1434G}}</ref>

=== Thermophotovoltaics ===
{{excerpt|Thermophotovoltaic}}

=== Solar module alignment ===

A number of solar modules may also be mounted vertically above each other in a tower, if the zenith distance of the Sun is greater than zero, and the tower can be turned horizontally as a whole and each module additionally around a horizontal axis. In such a tower the modules can follow the Sun exactly. Such a device may be described as a ladder mounted on a turnable disk. Each step of that ladder is the middle axis of a rectangular solar panel. In case the zenith distance of the Sun reaches zero, the "ladder" may be rotated to the north or the south to avoid a solar module producing a shadow on a lower one. Instead of an exactly vertical tower one can choose a tower with an axis directed to the polar star, meaning that it is parallel to the rotation axis of the [[Astronomy:Earth|Earth]]. In this case the angle between the axis and the Sun is always larger than 66 degrees. During a day it is only necessary to turn the panels around this axis to follow the Sun. Installations may be ground-mounted (and sometimes integrated with farming and grazing)<ref name="huliq.com">[http://www.huliq.com/18313/ge-invests-delivers-one-of-worlds-largest-solar-power-plants GE Invests, Delivers One of World's Largest Solar Power Plants]. Huliq.com (12 April 2007). Retrieved on 3 June 2012.</ref> or built into the roof or walls of a building (building-integrated photovoltaics).

Where land may be limited, PV can be deployed as floating solar. In 2008 the Far Niente Winery pioneered the world's first "floatovoltaic" system by installing 994 photovoltaic solar panels onto 130 pontoons and floating them on the winery's irrigation pond.<ref>[http://www.sfgate.com/bayarea/article/Winery-goes-solar-with-Floatovoltaics-3282171.php Winery goes solar with 'Floatovoltaics']. SFGate (29 May 2008). Retrieved on 31 May 2013.</ref><ref>[http://www.farniente.com/assets/files/pdfs/Floatovoltaic.pdf NAPA VALLEY'S FAR NIENTE WINERY INTRODUCES FIRST-EVER "FLOATOVOLTAIC" SOLAR ARRAY] {{webarchive|url=https://web.archive.org/web/20150316135710/http://farniente.com/assets/files/pdfs/Floatovoltaic.pdf |date=16 March 2015 }}. farniente.com</ref> A benefit of the set up is that the panels are kept at a lower temperature than they would be on land, leading to a higher efficiency of solar energy conversion. The floating panels also reduce the amount of water lost through evaporation and inhibit the growth of algae.<ref>[https://www.forbes.com/sites/williampentland/2011/08/15/napa-winery-pioneers-solar-floatovoltaics/ Napa Winery Pioneers Solar Floatovoltaics]. Forbes (18 April 2012). Retrieved on 31 May 2013.</ref>

[[Physics:Concentrator photovoltaics|Concentrator photovoltaics]] is a technology that contrary to conventional flat-plate PV systems uses lenses and curved mirrors to focus sunlight onto small, but highly efficient, multi-junction solar cells. These systems sometimes use [[Physics:Solar tracker|solar tracker]]s and a cooling system to increase their efficiency.

=== Efficiency ===
{{main|Physics:Solar cell efficiency}}
[[File:Best Research-Cell Efficiencies.png|thumb|upright=1.5|Best research-cell efficiencies]]
In 2019, the world record for solar cell efficiency at 47.1% was achieved by using [[Physics:Multi-junction solar cell|multi-junction]] [[Physics:Concentrator photovoltaics|concentrator]] solar cells, developed at National Renewable Energy Laboratory, Colorado, USA.<ref>{{Cite journal |last1=Geisz |first1=John F. |last2=France |first2=Ryan M. |last3=Schulte |first3=Kevin L. |last4=Steiner |first4=Myles A. |last5=Norman |first5=Andrew G. |last6=Guthrey |first6=Harvey L. |last7=Young |first7=Matthew R. |last8=Song |first8=Tao |last9=Moriarty |first9=Thomas |date=April 2020 |title=Six-junction III–V solar cells with 47.1% conversion efficiency under 143 Suns concentration |url=http://www.nature.com/articles/s41560-020-0598-5 |journal=Nature Energy |language=en |volume=5 |issue=4 |pages=326–335 |doi=10.1038/s41560-020-0598-5 |bibcode=2020NatEn...5..326G |osti=1659948 |s2cid=216289881 |issn=2058-7546}}</ref> The highest efficiencies achieved without concentration include a material by [[Company:Sharp Corporation|Sharp Corporation]] at 35.8% using a proprietary triple-junction manufacturing technology in 2009,<ref>[http://www.physorg.com/news175452895.html Sharp Develops Solar Cell with World's Highest Conversion Efficiency of 35.8%]. Physorg.com. 22 October 2009. Retrieved on 3 June 2012.</ref> and Boeing Spectrolab (40.7% also using a triple-layer design).

There is an ongoing effort to increase the conversion efficiency of PV cells and modules, primarily for competitive advantage. In order to increase the efficiency of solar cells, it is important to choose a semiconductor material with an appropriate [[Physics:Band gap|band gap]] that matches the solar spectrum. This will enhance the electrical and optical properties. Improving the method of charge collection is also useful for increasing the efficiency. There are several groups of materials that are being developed. Ultrahigh-efficiency devices (η>30%)<ref>Deb, Satyen K. (May 2000) [http://www.nrel.gov/docs/fy00osti/28060.pdf Recent Developments in High Efficiency PV cells]. nrel.gov</ref> are made by using GaAs and GaInP2 semiconductors with multijunction tandem cells. High-quality, single-crystal silicon materials are used to achieve high-efficiency, low cost cells (η>20%).

Recent developments in organic photovoltaic cells (OPVs) have made significant advancements in power conversion efficiency from 3% to over 15% since their introduction in the 1980s.<ref>{{Cite journal |doi=10.3390/polym6092473 |title=Towards High Performance Organic Photovoltaic Cells: A Review of Recent Development in Organic Photovoltaics |journal=Polymers |volume=6 |issue=9 |pages=2473–2509 |year=2014 |last1=Yu |first1=J. |last2=Zheng |first2=Y. |last3=Huang |first3=J. |doi-access=free}}</ref> To date, the highest reported power conversion efficiency ranges 6.7–8.94% for small molecule, 8.4–10.6% for polymer OPVs, and 7–21% for perovskite OPVs.<ref>{{Cite journal |doi=10.1038/nmat3160 |pmid=22057387 |title=Solution-processed small-molecule solar cells with 6.7% efficiency |journal=Nature Materials |volume=11 |issue=1 |pages=44–8 |year=2011 |last1=Sun |first1=Y. |last2=Welch |first2=G. C. |last3=Leong |first3=W. L. |last4=Takacs |first4=C. J. |last5=Bazan |first5=G. C. |last6=Heeger |first6=A. J. |bibcode=2012NatMa..11...44S}}</ref><ref>[http://www.dyesol.com/media/wysiwyg/Documents/2015-asx-announcements/2015-12-08-DYE0397_-_EPFL_achieves_21_efficiency.pdf EPFL Achieves 21% Efficiency for Perovskites]. dyesol.com (8 December 2015)</ref>  OPVs are expected to play a major role in the PV market. Recent improvements have increased the efficiency and lowered cost, while remaining environmentally-benign and renewable.

Several companies have begun embedding [[Physics:Power optimizer|power optimizer]]s into PV modules called [[Engineering:Smart module|smart module]]s. These modules perform [[Physics:Maximum power point tracking|maximum power point tracking]] (MPPT) for each module individually, measure performance data for monitoring, and provide additional safety features. Such modules can also compensate for shading effects, wherein a shadow falling across a section of a module causes the electrical output of one or more strings of cells in the module to decrease.<ref>St. John, Jeff (23 August 2012) [http://www.greentechmedia.com/articles/read/solar-electronics-panel-integration-and-the-bankability-challenge Solar Electronics, Panel Integration and the Bankability Challenge]. greentechmedia.com</ref>

One of the major causes for the decreased performance of cells is overheating. The efficiency of a solar cell declines by about 0.5% for every 1 degree Celsius increase in temperature. This means that a 100 degree increase in surface temperature could decrease the efficiency of a solar cell by about half. Self-cooling solar cells are one solution to this problem. Rather than using energy to cool the surface, pyramid and cone shapes can be formed from [[Chemistry:Silica|silica]], and attached to the surface of a solar panel. Doing so allows visible light to reach the [[Physics:Solar cell|solar cell]]s, but reflects [[Physics:Infrared|infrared]] rays (which carry heat).<ref>[http://www.cnn.com/2014/09/18/tech/innovation/solar-cells-of-the-future/ Self-cooling Solar Cells]. ''CNN''. 2014-09-18</ref>

== Advantages ==

*;Pollution and energy in production

The 122&nbsp;[[Orders of magnitude (power)#petawatt (1015 watts)|PW]] of sunlight reaching the Earth's surface is plentiful—almost 10,000 times more than the 13&nbsp;TW equivalent of average power consumed in 2005 by humans.<ref name="Smil">Smil, Vaclav (2006) [http://home.cc.umanitoba.ca/~vsmil/pdf_pubs/oecd.pdf Energy at the Crossroads]. oecd.org. Retrieved on 3 June 2012.</ref> This abundance leads to the suggestion that it will not be long before solar energy will become the world's primary energy source.<ref>[http://osumarion.osu.edu/news/dr-gordon-aubrecht-talks-renewables-tedxcolumbus Renewable Energy: Is the Future in Nuclear?] {{webarchive|url=https://web.archive.org/web/20140116123708/http://osumarion.osu.edu/news/dr-gordon-aubrecht-talks-renewables-tedxcolumbus |date=16 January 2014 }} Prof. Gordon Aubrecht (Ohio State at Marion) TEDxColumbus, The Innovators – 18 October 2012</ref> Additionally, solar radiation has the highest power density (global mean of 170&nbsp;W/m<sup>2</sup>) among renewable energies.<ref name="Smil" />{{Citation needed|date=January 2024}}

Solar power is pollution-free during use, which enables it to cut down on pollution when it is substituted for other energy sources. For example, MIT estimated that 52,000 people per year die prematurely in the U.S. from coal-fired power plant pollution<ref>{{cite web|url=https://news.mit.edu/2013/study-air-pollution-causes-200000-early-deaths-each-year-in-the-us-0829|title=Study: Air pollution causes 200,000 early deaths each year in the U.S|website=News.mit.edu|date=29 August 2013 |access-date=30 December 2017}}</ref> and all but one of these deaths could be prevented from using PV to replace coal.<ref>{{cite web|url=https://www.usatoday.com/videos/money/2017/06/01/-us-could-prevent-lot-deaths-switching-coal-solar/102405132/|title=The US could prevent a lot of deaths by switching from coal to solar|website=USA TODAY|access-date=30 December 2017}}</ref><ref>Potential lives saved by replacing coal with solar photovoltaic electricity production in the U.S. ''Renewable and Sustainable Energy Reviews'' 80 (2017), pp. 710–715. [https://www.academia.edu/33288631/Potential_Lives_Saved_by_Replacing_Coal_with_Solar_Photovoltaic_Electricity_Production_in_the open access]</ref> Production end-wastes and emissions are manageable using existing pollution controls. End-of-use recycling technologies are under development<ref>Nieuwlaar, Evert and Alsema, Erik. [http://www.energycrisis.com/apollo2/pvenv1997.pdf Environmental Aspects of PV Power Systems]. IEA PVPS Task 1 Workshop, 25–27 June 1997, Utrecht, The Netherlands</ref> and policies are being produced that encourage recycling from producers.<ref>{{cite journal|doi=10.1016/j.enpol.2010.07.023 |title=Producer Responsibility and Recycling Solar Photovoltaic Modules|year=2010|last1=McDonald|first1=N.C.|last2=Pearce|first2=J.M.|journal=Energy Policy|volume=38|issue=11|pages=7041–7047|url=https://hal.archives-ouvertes.fr/hal-02120502/file/Producer_Responsibility_and_Recycling_So.pdf}}</ref>

PV installations could ideally operate for 100 years or even more<ref>[http://www.hienergypeople.com/advantages-and-disadvantages-of-solar-energy/ Advantages and disadvantages of solar energy] {{webarchive|url=https://web.archive.org/web/20131226071416/http://www.hienergypeople.com/advantages-and-disadvantages-of-solar-energy/ |date=26 December 2013 }}. Retrieved on 25 December 2013.</ref> with little maintenance or intervention after their initial set-up, so after the initial [[Finance:Capital cost|capital cost]] of building any solar power plant, [[Finance:Operating cost|operating cost]]s are extremely low compared to existing power technologies.

Grid-connected solar electricity can be used locally thus reducing transmission/distribution losses (transmission losses in the US were approximately 7.2% in 1995).<ref>[http://www.climatetechnology.gov/library/2003/tech-options/tech-options-1-3-2.pdf U.S. Climate Change Technology Program – Transmission and Distribution Technologies] {{webarchive|url=https://web.archive.org/web/20070927173447/http://climatetechnology.gov/library/2003/tech-options/tech-options-1-3-2.pdf |date=27 September 2007 }}. (PDF) . Retrieved on 3 June 2012.</ref>

*;Solar cell research investment

Compared to fossil and nuclear energy sources, very little research money has been invested in the development of solar cells, so there is considerable room for improvement. Nevertheless, experimental high efficiency solar cells already have efficiencies of over 40% in case of concentrating photovoltaic cells<ref>[http://www.renewableenergyfocus.com/view/753/fraunhofer-41-1-efficiency-multi-junction-solar-cells/ Fraunhofer: 41.1% efficiency multi-junction solar cells]. renewableenergyfocus.com (28 January 2009).</ref> and efficiencies are rapidly rising while mass-production costs are rapidly falling.<ref>[http://solarcellsinfo.com/blog/archives/1018 Study Sees Solar Cost-Competitive In Europe By 2015]. Solar Cells Info (16 October 2007). Retrieved on 3 June 2012.</ref>

*;Housing subsidies

In some states of the United States, much of the investment in a home-mounted system may be lost if the homeowner moves and the buyer puts less value on the system than the seller. The city of Berkeley developed an innovative financing method to remove this limitation, by adding a tax assessment that is transferred with the home to pay for the solar panels.<ref>{{cite web |url= http://www.cityofberkeley.info/ContentDisplay.aspx?id=26580 |title= Berkeley FIRST Solar Financing – City of Berkeley, CA |website= cityofberkeley.info |access-date= 9 February 2009 |archive-url= https://web.archive.org/web/20130602054309/http://www.cityofberkeley.info/ContentDisplay.aspx?id=26580 |archive-date= 2 June 2013  }}</ref> Now known as PACE, Property Assessed Clean Energy, 30 U.S. states have duplicated this solution.<ref>[http://dsireusa.org/solar/solarpolicyguide/?id=26 DSIRE Solar Portal] {{Webarchive|url=https://web.archive.org/web/20120309110618/http://www.dsireusa.org/solar/solarpolicyguide/?id=26 |date=9 March 2012 }}. Dsireusa.org (4 April 2011). Retrieved on 3 June 2012.</ref>

== Disadvantages==

*Impact on electricity network
[[File:Renewables need flexible backup not baseload.png|thumb|Grids with high penetration of renewable energy sources generally need more flexible generation rather than baseload generation.]]
For behind-the-meter rooftop photovoltaic systems, the energy flow becomes two-way. When there is more local generation than consumption, electricity is exported to the grid, allowing for [[Finance:Net metering|net metering]]. However, electricity networks traditionally are not designed to deal with two-way energy transfer, which may introduce technical issues. An over-voltage issue may come out as the electricity flows from these PV households back to the network.<ref>{{cite journal |doi=10.3390/su10041224 |title=Power Quality and Rooftop-Photovoltaic Households: An Examination of Measured Data at Point of Customer Connection |journal=Sustainability |volume=10 |issue=4 |page=1224 |year=2018 |last1=Miller |first1=Wendy |last2=Liu |first2=Aaron |last3=Amin |first3=Zakaria |last4=Wagner |first4=Andreas |doi-access=free }}</ref> There are solutions to manage the over-voltage issue, such as regulating PV inverter power factor, new voltage and energy control equipment at electricity distributor level, re-conductor the electricity wires, demand side management, etc. There are often limitations and costs related to these solutions.

High generation during the middle of the day reduces the net generation demand, but higher peak net demand as the sun goes down can require rapid ramping of utility generating stations, producing a load profile called the [[Finance:Duck curve|duck curve]].

* Implications for electricity bill management and energy investment

There is no silver bullet in electricity or energy demand and bill management, because customers (sites) have different specific situations, e.g. different comfort/convenience needs, different electricity tariffs, or different usage patterns. Electricity tariff may have a few elements, such as daily access and metering charge, energy charge (based on kWh, MWh) or peak demand charge (e.g. a price for the highest 30min energy consumption in a month). PV is a promising option for reducing energy charges when electricity prices are reasonably high and continuously increasing, such as in Australia and Germany. However, for sites with peak demand charge in place, PV may be less attractive if peak demands mostly occur in the late afternoon to early evening, for example in residential communities. Overall, energy investment is largely an economic decision and it is better to make investment decisions based on systematic evaluation of options in operational improvement, energy efficiency, onsite generation and energy storage.<ref>L. Liu, W. Miller, and G. Ledwich. (2017) Solutions for reducing facilities electricity costs. Australian Ageing Agenda. 39-40. Available: https://www.australianageingagenda.com.au/2017/10/27/solutions-reducing-facility-electricity-costs/ {{Webarchive|url=https://web.archive.org/web/20190520033459/https://www.australianageingagenda.com.au/2017/10/27/solutions-reducing-facility-electricity-costs/ |date=20 May 2019 }}</ref><ref>{{cite journal |doi=10.1016/j.solener.2017.10.008 |title=Involving occupants in net-zero-energy solar housing retrofits: An Australian sub-tropical case study |journal=Solar Energy |volume=159 |pages=390–404 |year=2018 |last1=Miller |first1=Wendy |last2=Liu |first2=Lei Aaron |last3=Amin |first3=Zakaria |last4=Gray |first4=Matthew |bibcode=2018SoEn..159..390M }}</ref>

== See also ==
* Agrivoltaic
* American Solar Energy Society
* [[Physics:Anomalous photovoltaic effect|Anomalous photovoltaic effect]]
* {{sectionlink|Copper in renewable energy|Solar photovoltaic power generation}}
* [[Finance:Cost of electricity by source|Cost of electricity by source]]
* [[Finance:Energy demand management|Energy demand management]]
* {{sectionlink|Electromotive force|Solar cell}}
* List of photovoltaics companies
* [[Chemistry:Photoelectrochemical cell|Photoelectrochemical cell]]
* {{sectionlink|Quantum efficiency|Quantum efficiency of solar cells}}
* [[Social:Renewable energy commercialization|Renewable energy commercialization]]
* [[Physics:Solar cell fabric|Solar cell fabric]]
* Solar module quality assurance
* Solar photovoltaic monitoring
* Solar power by country
* [[Physics:Solar thermal energy|Solar thermal energy]]
* Theory of solar cell
{{div col end}}

== References ==
{{Reflist|30em}}

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


[[Category:Photovoltaics| ]]
[[Category:Quantum chemistry]]
[[Category:Electrochemistry]]
[[Category:Energy conversion]]
[[Category:Optoelectronics]]

{{Sourceattribution|Photovoltaics}}