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Solar power is the conversion of energy from sunlight into
electricity Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as describ ...
, either directly using
photovoltaics Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially ...
(PV) or indirectly using concentrated solar power.
Photovoltaic cells A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon.
convert light into an electric current using the
photovoltaic effect The photovoltaic effect is the generation of voltage and electric current in a material upon exposure to light. It is a physical and chemical phenomenon. The photovoltaic effect is closely related to the photoelectric effect. For both phenomena, ...
. Concentrated solar power systems use lenses or mirrors and
solar tracking A solar tracker is a device that orients a payload toward the Sun. Payloads are usually solar panels, parabolic troughs, fresnel reflectors, lenses or the mirrors of a heliostat. For flat-panel photovoltaic systems, trackers are used to m ...
systems to focus a large area of sunlight to a hot spot, often to drive a steam turbine. Photovoltaics were initially solely used as a source of electricity for small and medium-sized applications, from the calculator powered by a single solar cell to remote homes powered by an off-grid rooftop PV system. Commercial concentrated solar power plants were first developed in the 1980s. Since then, as the cost of solar electricity has fallen, grid-connected
solar PV systems A photovoltaic system, also PV system or solar power system, is an electric 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 co ...
have grown more or less exponentially. Millions of installations and gigawatt-scale photovoltaic power stations continue to be built, with half of new generation capacity being solar in 2021. As of 2021, solar generates 4% of the world's electricity, compared to 1% in 2015 when the Paris Agreement to limit climate change was signed. Along with
onshore wind A sea breeze or onshore breeze is any wind that blows from a large body of water toward or onto a landmass; it develops due to differences in air pressure created by the differing heat capacities of water and dry land. As such, sea breezes ar ...
, the cheapest
levelised cost of electricity The levelized cost of electricity (LCOE), or levelized cost of energy, is a measure of the average net present cost of electricity generation for a generator over its lifetime. It is used for investment planning and to compare different methods ...
is
utility-scale solar Utility-scale solar is large scale (sometimes defined as greater than 1 MW or sometimes 4 MWAC ) solar power either from: A photovoltaic power station at a scale large enough to be classified as 'utility-scale'; or Concentrated solar power whereas ...
. Much more low carbon power, such as solar, is urgently needed to limit climate change, but the International Energy Agency said in 2022 that more effort was needed for grid integration and the mitigation of policy, regulation and financing challenges.


Technologies

Solar power plants use one of two technologies: * Photovoltaic (PV) systems use solar panels, either on rooftops or in ground-mounted solar farms, converting sunlight directly into electric power. * Concentrated solar power (CSP) uses mirrors or lenses to concentrate sunlight to extreme heat to eventually make steam, which is converted into electricity by a
turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating ...
.


Photovoltaic cells

A
solar cell A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon.
, or photovoltaic cell, is a device that converts light into electric current using the
photovoltaic effect The photovoltaic effect is the generation of voltage and electric current in a material upon exposure to light. It is a physical and chemical phenomenon. The photovoltaic effect is closely related to the photoelectric effect. For both phenomena, ...
. The first solar cell was constructed by
Charles Fritts Charles Fritts (1850 – 1903) was the American inventor credited with creating the first working selenium cell in 1883. The world's first rooftop solar array, using Fritts' selenium cells, was installed in 1884 on a New York City rooftop. Fritt ...
in the 1880s. The German industrialist
Ernst Werner von Siemens Ernst Werner Siemens (von Siemens from 1888; ; ; 13 December 1816 – 6 December 1892) was a German electrical engineer, inventor and industrialist. Siemens's name has been adopted as the SI unit of electrical conductance, the siemens. He foun ...
was among those who recognized the importance of this discovery. In 1931, the German engineer Bruno Lange developed a photo cell using
silver selenide Silver selenide (Ag2Se) is the reaction product formed when selenium toning analog silver gelatine photo papers in photographic print toning. The selenium toner contains sodium selenite (Na2SeO3) as one of its active ingredients, which is the sour ...
in place of
copper oxide Copper oxide is a compound from the two elements copper and oxygen. Copper oxide may refer to: * Copper(I) oxide (cuprous oxide, Cu2O) * Copper(II) oxide Copper(II) oxide or cupric oxide is an inorganic compound with the formula CuO. A black so ...
, although the prototype
selenium Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, ...
cells converted less than 1% of incident light into electricity. Following the work of
Russell Ohl Russell Shoemaker Ohl (January 30, 1898 – March 20, 1987) was an American scientist who is generally recognized for patenting the modern solar cell (, "Light sensitive device"). Ohl was a notable semiconductor researcher prior to the invention o ...
in the 1940s, researchers Gerald Pearson, Calvin Fuller and Daryl Chapin created the
silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ta ...
solar cell in 1954. These early solar cells cost US$286/watt and reached efficiencies of 4.5–6%. In 1957,
Mohamed M. Atalla Mohamed M. Atalla ( ar, محمد عطاالله; August 4, 1924 – December 30, 2009) was an Egyptian-American engineer, physicist, cryptographer, inventor and entrepreneur. He was a semiconductor pioneer who made important contributions to ...
developed the process of silicon
surface passivation A surface, as the term is most generally used, is the outermost or uppermost layer of a physical object or space. It is the portion or region of the object that can first be perceived by an observer using the senses of sight and touch, and is ...
by
thermal oxidation In microfabrication, thermal oxidation is a way to produce a thin layer of oxide (usually silicon dioxide) on the surface of a wafer. The technique forces an oxidizing agent to diffuse into the wafer at high temperature and react with it. The ra ...
at
Bell Labs Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial Research and development, research and scientific developm ...
. The surface passivation process has since been critical to
solar cell efficiency Solar-cell efficiency refers to the portion of energy in the form of sunlight that can be converted via photovoltaics into electricity by the solar cell. The efficiency of the solar cells used in a photovoltaic system, in combination with lat ...
. over 90% of the market is
crystalline silicon Crystalline silicon or (c-Si) Is the crystalline forms of silicon, either polycrystalline silicon (poly-Si, consisting of small crystals), or monocrystalline silicon (mono-Si, a continuous crystal). Crystalline silicon is the dominant semiconduc ...
. The array of a photovoltaic system, or PV system, produces
direct current Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or eve ...
(DC) power which fluctuates with the sunlight's intensity. For practical use this usually requires conversion to
alternating current Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...
(AC), through the use of
inverters A power inverter, inverter or invertor is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC). The resulting AC frequency obtained depends on the particular device employed. Inverters do the opp ...
. Multiple solar cells are connected inside panels. Panels are wired together to form arrays, then tied to an inverter, which produces power at the desired voltage, and for AC, the desired frequency/phase. Many residential PV systems are connected to the grid wherever available, especially in developed countries with large markets. In these grid-connected PV systems, use of energy storage is optional. In certain applications such as satellites, lighthouses, or in developing countries, batteries or additional power generators are often added as back-ups. Such stand-alone power systems permit operations at night and at other times of limited sunlight.


Concentrated solar power

Concentrated solar power (CSP), also called "concentrated solar thermal", uses lenses or mirrors and tracking systems to concentrate sunlight, then use the resulting heat to generate electricity from conventional steam-driven turbines. A wide range of concentrating technologies exists: among the best known are the
parabolic trough A parabolic trough is a type of solar thermal collector that is straight in one dimension and curved as a parabola in the other two, lined with a polished metal mirror. The sunlight which enters the mirror parallel to its plane of symmetry is foc ...
, the compact linear Fresnel reflector, the
dish Stirling Solar thermal energy (STE) is a form of energy and a technology for harnessing solar energy to generate thermal energy for use in industry, and in the residential and commercial sectors. Solar thermal collectors are classified by the United St ...
and the
solar power tower A solar power tower, also known as 'central tower' power plant or ' heliostat' power plant, is a type of solar furnace using a tower to receive focused sunlight. It uses an array of flat, movable mirrors (called heliostats) to focus the sun's r ...
. Various techniques are used to track the sun and focus light. In all of these systems a
working fluid For fluid power, a working fluid is a gas or liquid that primarily transfers force, motion, or mechanical energy. In hydraulics, water or hydraulic fluid transfers force between hydraulic components such as hydraulic pumps, hydraulic cylinders, ...
is heated by the concentrated sunlight, and is then used for power generation or energy storage.Martin and Goswami (2005), p. 45 Thermal storage efficiently allows overnight electricity generation, thus complementing PV. CSP generates a very small share of solar power and in 2022 the IEA said that CSP should be better paid for its storage. the LCOE of CSP is over twice that of PV, however their very high temperatures may prove useful to help decarbonize industries (perhaps via hydrogen) which need to be hotter than electricity can provide.


Hybrid systems

A hybrid system combines solar with energy storage and/or one or more other forms of generation. Hydro, wind and batteries are commonly combined with solar. The combined generation may enable the system to vary power output with demand, or at least smooth the solar power fluctuation. There is a lot of hydro worldwide, and adding solar panels on or around existing hydro reservoirs is particularly useful, because hydro is usually more flexible than wind and cheaper at scale than batteries, and existing power lines can sometimes be used.


Development and deployment


Early days

The early development of solar technologies starting in the 1860s was driven by an expectation that coal would soon become scarce, such as experiments by Augustin Mouchot.
Charles Fritts Charles Fritts (1850 – 1903) was the American inventor credited with creating the first working selenium cell in 1883. The world's first rooftop solar array, using Fritts' selenium cells, was installed in 1884 on a New York City rooftop. Fritt ...
installed the world's first rooftop photovoltaic solar array, using 1%-efficient
selenium Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, ...
cells, on a New York City roof in 1884. However, development of solar technologies stagnated in the early 20th century in the face of the increasing availability, economy, and utility of coal and
petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...
. The first satellite with solar panels was launched in 1957. By the 1970s, solar power was being used on satellites, but the cost of solar power was considered to be unrealistic for conventional applications. In 1974 it was estimated that only six private homes in all of North America were entirely heated or cooled by functional solar power systems. However, the
1973 oil embargo The 1973 oil crisis or first oil crisis began in October 1973 when the members of the Organization of Arab Petroleum Exporting Countries (OAPEC), led by Saudi Arabia, proclaimed an oil embargo. The embargo was targeted at nations that had supp ...
and
1979 energy crisis The 1979 oil crisis, also known as the 1979 Oil Shock or Second Oil Crisis, was an energy crisis caused by a drop in oil production in the wake of the Iranian Revolution. Although the global oil supply only decreased by approximately four per ...
caused a reorganization of energy policies around the world and brought renewed attention to developing solar technologies. Deployment strategies focused on incentive programs such as the Federal Photovoltaic Utilization Program in the US and the Sunshine Program in Japan. Other efforts included the formation of research facilities in the United States (SERI, now
NREL The National Renewable Energy Laboratory (NREL) in the US specializes in the research and development of renewable energy, energy efficiency, energy systems integration, and sustainable transportation. NREL is a federally funded research and ...
), Japan ( NEDO), and Germany ( Fraunhofer ISE). Between 1970 and 1983 installations of photovoltaic systems grew rapidly. In the United States, President
Jimmy Carter James Earl Carter Jr. (born October 1, 1924) is an American politician who served as the 39th president of the United States from 1977 to 1981. A member of the Democratic Party, he previously served as the 76th governor of Georgia from 1 ...
set a target of producing 20% of U.S. energy from solar by the year 2000, but his successor, Ronald Reagan, removed the funding for research into renewables. Falling oil prices in the early 1980s moderated the
growth of photovoltaics Worldwide growth of photovoltaics has been close to exponential between 1992 and 2018. During this period of time, photovoltaics (PV), also known as solar PV, evolved from a niche market of small-scale applications to a mainstream electricit ...
from 1984 to 1996.


Mid-1990s to 2010

In the mid-1990s development of both, residential and commercial
rooftop solar A rooftop solar power system, or rooftop PV system, is a photovoltaic (PV) system that has its electricity-generating solar panels mounted on the rooftop of a residential or commercial building or structure. The various components of such a syst ...
as well as utility-scale photovoltaic power stations began to accelerate again due to supply issues with oil and natural gas,
global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
concerns, and the improving economic position of PV relative to other energy technologies. In the early 2000s, the adoption of
feed-in tariff A feed-in tariff (FIT, FiT, standard offer contract,Couture, T., Cory, K., Kreycik, C., Williams, E., (2010)Policymaker's Guide to Feed-in Tariff Policy Design National Renewable Energy Laboratory, U.S. Dept. of Energy advanced renewable tariff, ...
s—a policy mechanism, that gives renewables priority on the grid and defines a fixed price for the generated electricity—led to a high level of investment security and to a soaring number of PV deployments in Europe.


2010s

For several years, worldwide growth of solar PV was driven by European deployment, but then shifted to Asia, especially China and Japan, and to a growing number of countries and regions all over the world. The largest manufacturers were located in China. Although concentrated solar power grew more than tenfold it remained a tiny proportion of the total, because the cost of utility-scale solar PV fell by 85%, to below CSP cost which fell only 68%.


2020s

Despite the rising cost of materials, such as
polysilicon Polycrystalline silicon, or multicrystalline silicon, also called polysilicon, poly-Si, or mc-Si, is a high purity, polycrystalline form of silicon, used as a raw material by the solar photovoltaic and electronics industry. Polysilicon is produce ...
, during the
2021–2022 global energy crisis The 2021–2022 global energy crisis began in the aftermath of the COVID-19 pandemic in 2021, with much of the globe facing shortages and increased prices in oil, gas and electricity markets. The crisis was caused by a variety of economic factor ...
; the cost of some other energy sources, such as natural gas, rose more thus making utility scale solar the cheapest energy source in many countries. 1 TW had been installed by 2022. However growth continued to be hindered by fossil-fuel subsidies.


Current status

About half of installed capacity is utility scale. According to the IEA not enough CSP is being built.


Forecasts

Most new renewable capacity between 2022 and 2027 is forecast to be solar, surpassing coal as the largest source of installed power capacity. Utility scale is forecast to become the largest capacity in all regions except sub-Saharan Africa. According to a 2021 study global electricity generation potential of
rooftop solar A rooftop solar power system, or rooftop PV system, is a photovoltaic (PV) system that has its electricity-generating solar panels mounted on the rooftop of a residential or commercial building or structure. The various components of such a syst ...
panels is estimated at 27 PWh per year at cost ranging from $40 (Asia) to $240 per MWh (US, Europe). Its practical realization will however depend on the availability and cost of scalable electricity storage solutions.


Photovoltaic power stations


Concentrating solar power stations

Commercial concentrating solar power (CSP) plants, also called "solar thermal power stations", were first developed in the 1980s. The 377  MW Ivanpah Solar Power Facility, located in California's Mojave Desert, is the world's largest solar thermal power plant project. Other large CSP plants include the
Solnova Solar Power Station The Solnova Solar Power Station is a large CSP power station made up of five separate units of each. The facility is part of the Solucar Complex, in Sanlúcar la Mayor, in Spain, the same area where the PS20 solar power tower is also located. ...
(150 MW), the
Andasol solar power station The Andasol solar power station is a 150- megawatt (MW) concentrated solar power station and Europe's first commercial plant to use parabolic troughs. It is located near Guadix in Andalusia, Spain, and its name is a portmanteau of Andalusia and ...
(150 MW), and
Extresol Solar Power Station The Extresol Solar Power Station is a 150 megawatt (MW) commercial concentrated solar thermal power plant, located in Torre de Miguel Sesmero in the province of Badajoz, Extremadura, Spain. The power station consists of three different sys ...
(150 MW), all in Spain. The principal advantage of CSP is the ability to efficiently add thermal storage, allowing the dispatching of electricity over up to a 24-hour period. Since peak electricity demand typically occurs at about 5 pm, many CSP power plants use 3 to 5 hours of thermal storage.


Economics


Cost per watt

The typical cost factors for solar power include the costs of the modules, the frame to hold them, wiring, inverters, labour cost, any land that might be required, the grid connection, maintenance and the solar insolation that location will receive. Photovoltaic systems use no fuel, and modules typically last 25 to 40 years. Thus upfront capital and financing costs make up 80 to 90% of the cost of solar power. Some countries are considering price caps, whereas others prefer contracts for difference.


Installation prices

Expenses of high power band solar modules has greatly decreased over time. Beginning in 1982, the cost per kW was approximately 27,000 American dollars, and in 2006 the cost dropped to approximately 4,000 American dollars per kW. The PV system in 1992 cost approximately 16,000 American dollars per kW and it dropped to approximately 6,000 American dollars per kW in 2008. In 2021 in the US, residential solar cost from 2 to 4 dollars/watt (but solar shingles cost much more) and utility solar costs were around $1/watt.


Productivity by location

The productivity of solar power in a region depends on solar irradiance, which varies through the day and year and is influenced by
latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...
and
climate Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologi ...
. PV system output power also depends on ambient temperature, wind speed, solar spectrum, the local soiling conditions, and other factors. Onshore
wind power Wind power or wind energy is mostly the use of wind turbines to generate electricity. Wind power is a popular, sustainable, renewable energy source that has a much smaller impact on the environment than burning fossil fuels. Historically ...
tends to be the cheapest source of electricity in Northern Eurasia, Canada, some parts of the United States, and
Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and g ...
in Argentina: whereas in other parts of the world mostly solar power (or less often a combination of wind, solar and other low carbon energy) is thought to be best. The locations with highest annual solar irradiance lie in the arid tropics and subtropics. Deserts lying in low latitudes usually have few clouds, and can receive sunshine for more than ten hours a day. These hot deserts form the ''Global Sun Belt'' circling the world. This belt consists of extensive swathes of land in
Northern Africa North Africa, or Northern Africa is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region, and it is sometimes defined as stretching from the Atlantic shores of Mauritania in t ...
,
Southern Africa Southern Africa is the southernmost subregion of the African continent, south of the Congo and Tanzania. The physical location is the large part of Africa to the south of the extensive Congo River basin. Southern Africa is home to a number o ...
,
Southwest Asia Western Asia, West Asia, or Southwest Asia, is the westernmost subregion of the larger geographical region of Asia, as defined by some academics, UN bodies and other institutions. It is almost entirely a part of the Middle East, and includes Ana ...
,
Middle East The Middle East ( ar, الشرق الأوسط, ISO 233: ) is a geopolitical region commonly encompassing Arabia (including the Arabian Peninsula and Bahrain), Asia Minor (Asian part of Turkey except Hatay Province), East Thrace (Europ ...
, and Australia, as well as the much smaller deserts of
North North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating direction or geography. Etymology The word ''north ...
and
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...
. So solar is (or is predicted to become) the cheapest source of energy in all of Central America, Africa, the Middle East, India, South-east Asia, Australia, and several other places. Different measurements of solar irradiance (direct normal irradiance, global horizontal irradiance) are mapped below : File:SolarGIS-Solar-map-North-America-en.png, North America File:SolarGIS-Solar-map-Latin-America-en.png, South America File:SolarGIS-Solar-map-Europe-en.png, Europe File:SolarGIS-Solar-map-Africa-and-Middle-East-en.png, Africa and Middle East File:SolarGIS-Solar-map-South-And-South-East-Asia-en.png, South and South-East Asia File:SolarGIS-Solar-map-Australia-en.png, Australia File:SolarGIS-Solar-map-World-map-en.png, World


Self consumption

In cases of self-consumption of solar energy, the payback time is calculated based on how much electricity is not purchased from the grid. However, in many cases, the patterns of generation and consumption do not coincide, and some or all of the energy is fed back into the grid. The electricity is sold, and at other times when energy is taken from the grid, electricity is bought. The relative costs and prices obtained affect the economics. In many markets, the price paid for sold PV electricity is significantly lower than the price of bought electricity, which incentivizes self consumption. Moreover, separate self consumption incentives have been used in e.g. Germany and Italy. Grid interaction regulation has also included limitations of grid feed-in in some regions in Germany with high amounts of installed PV capacity. By increasing self consumption, the grid feed-in can be limited without curtailment, which wastes electricity. A good match between generation and consumption is key for high self-consumption. The match can be improved with batteries or controllable electricity consumption. However, batteries are expensive and profitability may require the provision of other services from them besides self consumption increase. Hot water storage tanks with electric heating with heat pumps or resistance heaters can provide low-cost storage for self consumption of solar power. Shiftable loads, such as dishwashers, tumble dryers and washing machines, can provide controllable consumption with only a limited effect on the users, but their effect on self-consumption of solar power may be limited.


Energy pricing, incentives and taxes

The original political purpose of incentive policies for PV was to facilitate an initial small-scale deployment to begin to grow the industry, even where the cost of PV was significantly above grid parity, to allow the industry to achieve the economies of scale necessary to reach grid parity. Since reaching grid parity some policies are implemented to promote national energy independence, high tech job creation and reduction of CO2 emissions. Three incentive mechanisms are often used in combination as investment subsidies: the authorities refund part of the cost of installation of the system, the electricity utility buys PV electricity from the producer under a multiyear contract at a guaranteed rate, and Solar Renewable Energy Certificates (SRECs). Financial incentives for photovoltaics differ across countries, including Australia, China,
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
,
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
, Japan, and the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...
and even across states within the US.


Net metering

In net metering the price of the electricity produced is the same as the price supplied to the consumer, and the consumer is billed on the difference between production and consumption. Net metering can usually be done with no changes to standard electricity meters, which accurately measure power in both directions and automatically report the difference, and because it allows homeowners and businesses to generate electricity at a different time from consumption, effectively using the grid as a giant storage battery. With net metering, deficits are billed each month while surpluses are rolled over to the following month. Best practices call for perpetual roll over of kWh credits. Excess credits upon termination of service are either lost or paid for at a rate ranging from wholesale to retail rate or above, as can be excess annual credits.


Taxes

In some countries tariffs (import taxes) are imposed on imported solar panels.


Grid integration

The overwhelming majority of electricity produced worldwide is used immediately because traditional generators can adapt to demand and storage is usually more expensive. Both solar power and
wind power Wind power or wind energy is mostly the use of wind turbines to generate electricity. Wind power is a popular, sustainable, renewable energy source that has a much smaller impact on the environment than burning fossil fuels. Historically ...
are sources of variable renewable power, meaning that all available output must be used locally, carried on transmission lines elsewhere to be used, or stored (e.g. in a battery). Since solar energy is not available at night, storing its energy is potentially an important issue particularly in off-grid and for future
100% renewable energy 100% renewable energy means getting all energy from renewable resources. The endeavor to use 100% renewable energy for electricity, heating, cooling and transport is motivated by climate change, pollution and other environmental issues ...
scenarios to have continuous electricity availability. Solar electricity is inherently variable but somewhat predictable by time of day, location, and seasons. Solar is intermittent due to day/night cycles and unpredictable weather. How much of a special challenge solar power is in any given electric utility varies significantly. In places with hot summers and mild winters, solar is well matched to daytime cooling demands. Conventional hydroelectric dams work very well in conjunction with solar power; water can be held back or released from a reservoir as required. Where suitable geography is not available, pumped-storage hydroelectricity can use solar power to pump water to a high reservoir on sunny days, then the energy is recovered at night and in bad weather by releasing water via a hydroelectric plant to a low reservoir where the cycle can begin again.


Energy storage

Concentrated solar power plants may use thermal storage to store solar energy, such as in high-temperature molten salts. These salts are an effective storage medium because they are low-cost, have a high specific heat capacity, and can deliver heat at temperatures compatible with conventional power systems. This method of energy storage is used, for example, by the Solar Two power station, allowing it to store 1.44  TJ in its 68 m3 storage tank, enough to provide full output for close to 39 hours, with an efficiency of about 99%. In stand alone PV systems batteries are traditionally used to store excess electricity. With
grid-connected photovoltaic power system A grid-connected photovoltaic system, or grid-connected PV system is an electricity generating solar PV power system that is connected to the utility grid. A grid-connected PV system consists of solar panels, one or several inverters, a power c ...
, excess electricity can be sent to the electrical grid. Net metering and
feed-in tariff A feed-in tariff (FIT, FiT, standard offer contract,Couture, T., Cory, K., Kreycik, C., Williams, E., (2010)Policymaker's Guide to Feed-in Tariff Policy Design National Renewable Energy Laboratory, U.S. Dept. of Energy advanced renewable tariff, ...
programs give these systems a credit for the electricity they produce. This credit offsets electricity provided from the grid when the system cannot meet demand, effectively trading with the grid instead of storing excess electricity. When wind and solar are a small fraction of the grid power, other generation techniques can adjust their output appropriately, but as these forms of variable power grow, additional balance on the grid is needed. As prices are rapidly declining, PV systems increasingly use rechargeable batteries to store a surplus to be later used at night. Batteries used for grid-storage can stabilize the electrical grid by leveling out peak loads for a few hours. In the future, less expensive batteries could play an important role on the electrical grid, as they can charge during periods when generation exceeds demand and feed their stored energy into the grid when demand is higher than generation. Common battery technologies used in today's home PV systems include nickel-cadmium, lead-acid,
nickel metal hydride Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to r ...
, and
lithium-ion A lithium-ion or Li-ion battery is a type of rechargeable battery which uses the reversible reduction of lithium ions to store energy. It is the predominant battery type used in portable consumer electronics and electric vehicles. It also se ...
.Lithium-ion batteries have the potential to replace lead-acid batteries in the near future, as they are being intensively developed and lower prices are expected due to
economies of scale In microeconomics, economies of scale are the cost advantages that enterprises obtain due to their scale of operation, and are typically measured by the amount of output produced per unit of time. A decrease in cost per unit of output enables ...
provided by large production facilities such as the
Gigafactory 1 Gigafactory Nevada (also known as Giga Nevada or Gigafactory 1) is a lithium-ion battery and electric vehicle component factory in Storey County, Nevada, US. The facility, located east of Reno, is owned and operated by Tesla, Inc., and suppl ...
. In addition, the Li-ion batteries of plug-in electric cars may serve as future storage devices in a
vehicle-to-grid Vehicle-to-grid (V2G), also known as Vehicle-to-home (V2H) or Vehicle-to-load (V2L) describes a system in which plug-in electric vehicles (PEV) sell demand response services to the grid. Demand services are either delivering electricity or by red ...
system. Since most vehicles are parked an average of 95% of the time, their batteries could be used to let electricity flow from the car to the power lines and back. Other rechargeable batteries used for
distributed Distribution may refer to: Mathematics *Distribution (mathematics), generalized functions used to formulate solutions of partial differential equations *Probability distribution, the probability of a particular value or value range of a varia ...
PV systems include, sodium–sulfur and vanadium redox batteries, two prominent types of a
molten salt Molten salt is salt which is solid at standard temperature and pressure but enters the liquid phase due to elevated temperature. Regular table salt has a melting point of 801 °C (1474°F) and a heat of fusion of 520 J/g.Journal of Chemical T ...
and a flow battery, respectively.


Other technologies

In an electricity system without grid energy storage, generation from stored fuels (coal, biomass, natural gas, nuclear) must go up and down in reaction to the rise and fall of solar electricity (see
load following power plant A load-following power plant, regarded as producing mid-merit or mid-priced electricity, is a power plant that adjusts its power output as demand for electricity fluctuates throughout the day. Load-following plants are typically in between base lo ...
). While hydroelectric and natural gas plants can quickly respond to changes in load, coal, biomass and nuclear plants usually take considerable time to respond to load and can only be scheduled to follow the predictable variation. Depending on local circumstances, beyond about 20–40% of total generation, grid-connected intermittent sources like solar tend to require investment in some combination of grid interconnections, energy storage or
demand side management Energy demand management, also known as demand-side management (DSM) or demand-side response (DSR), is the modification of consumer demand for energy through various methods such as financial incentives and behavioral change through education. Us ...
. In countries with high solar generation, such as Australia and Germany, electricity prices have been known to go negative in the middle of the day when solar is generating a lot of power, thus incentivizing new
battery storage A battery storage power station is a type of energy storage power station that uses a group of batteries to store electrical energy. Battery storage is the fastest responding dispatchable source of power on electric grids, and it is used to stab ...
. The combination of wind and solar PV has the advantage that the two sources complement each other because the peak operating times for each system occur at different times of the day and year. The power generation of such
solar hybrid power systems Hybrid power are combinations between different technologies to produce power. In power engineering, the term 'hybrid' describes a combined power and energy storage system. Examples of power producers used in hybrid power are photovoltaics, ...
is therefore more constant and fluctuates less than each of the two component subsystems. Solar power is seasonal, particularly in northern/southern climates, away from the equator, suggesting a need for long term seasonal storage in a medium such as hydrogen or pumped hydroelectric.


Environmental effects

A very small proportion of solar power is concentrated solar power. Concentrated solar power may use much more water than gas-fired power. This can be a problem, as this type of solar power needs strong sunlight so is often built in deserts. Solar power is cleaner than electricity from fossil fuels: solar power does not lead to any harmful emissions during operation, but the production of the panels leads to some amount of pollution. A 2021 study estimated the carbon footprint of manufacturing monocrystalline panels at 515 g CO2/kWp in the US and 740 g CO2/kWp in China, but this is expected to fall as manufacturers use more clean electricity and recycled materials. Solar power carries an upfront cost to the environment via production with a carbon payback time of a few years , but offers clean energy for the rest of its 30 year lifetime. The life-cycle greenhouse-gas emissions of solar farms are less than 50 gram (g) per kilowatt-hour (kWh), but with
battery storage A battery storage power station is a type of energy storage power station that uses a group of batteries to store electrical energy. Battery storage is the fastest responding dispatchable source of power on electric grids, and it is used to stab ...
could be up to 150 g/kWh. In contrast, a combined cycle gas-fired power plant without
carbon capture and storage Carbon capture and storage (CCS) or carbon capture and sequestration is the process of capturing carbon dioxide (CO2) before it enters the atmosphere, transporting it, and storing it (carbon sequestration) for centuries or millennia. Usually th ...
emits around 500 g/kWh, and a coal-fired power plant about 1000 g/kWh. Similar to all energy sources where their total life cycle emissions are mostly from construction, the switch to low carbon power in the manufacturing and transportation of solar devices would further reduce carbon emissions. Life-cycle
surface power density In physics and engineering, surface power density is power per unit area. Applications * The intensity of electromagnetic radiation can be expressed in W/m2. An example of such a quantity is the solar constant. * Wind turbines are often compared ...
of solar power varies a lot but averages about 7 W/m2, compared to about 240 for
nuclear power Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced ...
and 480 for gas. However when the land required for gas extraction and processing is accounted for gas power is estimated to have not much higher power density than solar. PV requires much larger amounts of land surface to produce the same nominal amount of energy as sources with higher surface power density and capacity factor. According to a 2021 study, obtaining 25 to 80% of electricity from solar farms in their own territory by 2050 would require the panels to cover land ranging from 0.5 to 2.8% of the
European Union The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been de ...
, 0.3 to 1.4% in
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
, and 1.2 to 5.2% in Japan and
South Korea South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korean Peninsula and sharing a land border with North Korea. Its western border is formed by the Yellow Sea, while its eas ...
. Occupation of such large areas for PV farms could drive residential opposition as well as lead to deforestation, removal of vegetation and conversion of farm land. However some countries, such as South Korea and Japan, use land for agriculture under PV, or floating solar. Worldwide land use has minimal ecological impact. Land use can be reduced to the level of gas power by installing on buildings and other built up areas. Harmful materials are used in the production of solar panels, but in generally in small amounts. the environmental impact of perovskite is hard to estimate, but there is some concern that
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
may become a problem. A 2021 International Energy Agency study projects the demand for
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
will double by 2040. The study cautions that supply needs to increase rapidly to match demand from large-scale deployment of solar and required grid upgrades. More
tellurium Tellurium is a chemical element with the symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionall ...
and
indium Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts ...
may also be needed and recycling may help. As solar panels are sometimes replaced with more efficient panels, the second-hand panels are sometimes reused in developing countries, for example in
Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
. Several countries have specific regulations for the recycling of solar panels. Although maintenance cost is already low compared to other energy sources, some academics have called for solar power systems to be designed to be more
repairable A repairable component is a component of a finished good that can be designated for repair. Overview Repairable components tend to be more expensive than non-repairable components (consumables). This is because for items that are inexpensive to ...
.


Political issues

over 40% of global polysilicon manufacturing capacity is in
Xinjiang Xinjiang, SASM/GNC: ''Xinjang''; zh, c=, p=Xīnjiāng; formerly romanized as Sinkiang (, ), officially the Xinjiang Uygur Autonomous Region (XUAR), is an autonomous region of the People's Republic of China (PRC), located in the northwest ...
in China, which raises concerns about human rights violations ( Xinjang internment camps) as well as supply chain dependency. However solar cannot be cut off, unlike oil and gas, so can contribute to
energy security Energy security is the association between national security and the availability of natural resources for energy consumption. Access to (relatively) cheap energy has become essential to the functioning of modern economies. However, the uneven d ...
.


See also

*
100% renewable energy 100% renewable energy means getting all energy from renewable resources. The endeavor to use 100% renewable energy for electricity, heating, cooling and transport is motivated by climate change, pollution and other environmental issues ...
*
Cost of electricity by source Different methods of electricity generation can incur a variety of different costs, which can be divided into three general categories: 1) wholesale costs, or all costs paid by utilities associated with acquiring and distributing electricity to ...
*
Index of solar energy articles This is a list of solar energy topics. A * Air mass coefficient * Artificial photosynthesis B * BP Solar * BrightSource Energy * Building-integrated photovoltaics C * Carbon nanotubes in photovoltaics * Central solar heating plant * Commu ...
*
List of cities by sunshine duration The following is a list of cities by sunshine duration. Sunshine duration is a climatological indicator, measuring duration of sunshine in given period (usually, a day or a year) for a given location on Earth, typically expressed as an average ...
*
List of photovoltaic power stations The following is a list of photovoltaic power stations that are larger than 300 megawatts (MW) in current net capacity.Note that nominal power may be AC or DC, depending on the plant, and therefore any totals quoted are hybrid. SeAC-DC conundru ...
*
List of solar thermal power stations This is a list of the largest facilities generating electricity through the use of solar thermal power, specifically concentrated solar power. Operational Under construction Announced Cancelled Decommissioned * Eurelios p ...
*
Renewable energy commercialization Renewable energy commercialization involves the deployment of three generations of renewable energy technologies dating back more than 100 years. First-generation technologies, which are already mature and economically competitive, include b ...
* Solar energy *
Solar lamp A solar lamp, also known as a solar light or solar lantern, is a lighting system composed of an LED lamp, solar panels, battery, charge controller and there may also be an inverter. The lamp operates on electricity from batteries, charged throug ...
*
Solar vehicle A solar vehicle or solar electric vehicle is an electric vehicle powered completely or significantly by direct solar energy. Usually, photovoltaic (PV) cells contained in solar panels convert the sun's energy directly into electric energy. T ...
* Sustainable energy *
Timeline of solar cells In the 19th century, it was observed that the sunlight striking certain materials generates detectable electric current – the photoelectric effect. This discovery laid the foundation for solar cells. Solar cells have gone on to be used in many ap ...


References


Further reading

*


External links


Solar energy and the environment
at U.S. Energy Information Administration {{DEFAULTSORT:Solar Power Bright green environmentalism Energy conversion Sustainable energy
Power Power most often refers to: * Power (physics), meaning "rate of doing work" ** Engine power, the power put out by an engine ** Electric power * Power (social and political), the ability to influence people or events ** Abusive power Power may a ...
Renewable energy