Editing Solar energy (section)

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

Solar radiation is absorbed by the Earth's land surface, oceans – which cover about 71% of the globe – and atmosphere. Warm air containing evaporated water from the oceans rises, causing [[atmospheric circulation]] or [[convection]]. When the air reaches a high altitude, where the temperature is low, water vapor condenses into clouds, which rain onto the Earth's surface, completing the [[water cycle]]. The [[latent heat]] of water condensation amplifies convection, producing atmospheric phenomena such as wind, [[cyclone]]s and [[anticyclone]]s.<ref>{{cite web|title=Radiation Budget|date=17 October 2006|publisher=NASA Langley Research Center|url=http://marine.rutgers.edu/mrs/education/class/yuri/erb.html|access-date=29 September 2007}}</ref> Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14&nbsp;°C.<ref>{{cite web|author=Somerville, Richard|title=Historical Overview of Climate Change Science|url=http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter1.pdf|publisher=Intergovernmental Panel on Climate Change|access-date=29 September 2007}}</ref> By [[photosynthesis]], green plants convert solar energy into chemically stored energy, which produces food, wood and the [[biomass]] from which [[fossil fuels]] are derived.<ref>{{cite web|author=Vermass, Wim|title=An Introduction to Photosynthesis and Its Applications|publisher=Arizona State University|url=http://photoscience.la.asu.edu/photosyn/education/photointro.html|access-date=29 September 2007|url-status=dead|archive-url=https://web.archive.org/web/19981203020943/http://photoscience.la.asu.edu/photosyn/education/photointro.html|archive-date=3 December 1998}}</ref>

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

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

The potential solar energy that could be used by humans differs from the amount of solar energy present near the surface of the planet because factors such as geography, time variation, cloud cover, and the land available to humans limit the amount of solar energy that we can acquire. In 2021, [[Carbon Tracker Initiative]] estimated the land area needed to generate all our energy from solar alone was 450,000 [[Square kilometre|km<sup>2</sup>]] — or about the same as the area of [[Sweden]], or the area of [[Morocco]], or the area of [[California]] (0.3% of the Earth's total land area).<ref>{{Cite web|last=Bond|first=Kingsmill|date=April 2021|title=The sky's the limit|url=https://epbr.com.br/wp-content/uploads/2021/04/Sky-the-limit-report_Apr21-compressed.pdf|url-status=live|archive-url=https://web.archive.org/web/20210430191920/https://epbr.com.br/wp-content/uploads/2021/04/Sky-the-limit-report_Apr21-compressed.pdf|archive-date=April 30, 2021|access-date=October 22, 2021|website=epbr|publisher=Carbon Tracker Initiative|page=6}}</ref>

Solar technologies are categorized as either passive or active depending on the way they capture, convert and distribute sunlight and enable solar energy to be harnessed at different levels around the world, mostly depending on the distance from the Equator. Although solar energy refers primarily to the use of solar radiation for practical ends, all types of renewable energy, other than [[geothermal power]] and [[tidal power]], are derived either directly or indirectly from the Sun.

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

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

{| class="wikitable" style="text-align: center;"
|+Annual solar energy potential by region (Exajoules) <ref name="World Energy Assessment" />
! Region !! North America !! Latin America<br>and Caribbean !! Western<br>Europe !! Central and<br>Eastern Europe !! Former<br>Soviet Union !! Middle East and<br>North Africa !! Sub-Saharan<br>Africa !! Pacific<br>Asia !! South<br>Asia !! Centrally<br>planned<br>Asia !! Pacific<br>OECD
|-
| align=left | Minimum || 181.1 || 112.6 || 25.1 || 4.5 || 199.3 || 412.4 || 371.9 || 41.0 || 38.8 || 115.5 || 72.6
|-
| align=left | Maximum || 7,410 || 3,385 || 914 || 154 || 8,655 || 11,060 || 9,528 || 994 || 1,339 || 4,135 || 2,263
|-
! colspan=12 style="font-weight: normal; text-align: left; padding: 6px 4px; font-size: 92%;" |''Notes:''
* Total global annual solar energy potential amounts to 1,575 EJ (minimum) to 49,837 EJ (maximum)
* Data reflects assumptions of annual clear sky irradiance, annual average sky clearance, and available land area. All figures given in Exajoules.
''Quantitative relation'' of global solar potential vs. the world's [[primary energy consumption]]:
* Ratio of potential vs. current consumption (402 EJ) as of year: 3.9 (minimum) to 124 (maximum)
* Ratio of potential vs. projected consumption by 2050 (590–1,050 EJ): 1.5–2.7 (minimum) to 47–84 (maximum)
* Ratio of potential vs. projected consumption by 2100 (880–1,900 EJ): 0.8–1.8 (minimum) to 26–57 (maximum)
''Source:'' [[United Nations Development Programme]] – World Energy Assessment (2000)<ref name="World Energy Assessment" />
|}