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Solar power is the conversion of
renewable energy Renewable energy is energy that is collected from renewable resource File:Global Vegetation.jpg, Global vegetation A renewable resource, also known as a flow resource, is a natural resource which will replenish to replace the portion resou ...
from
sunlight Sunlight is a portion of the given off by the , in particular , , and light. On , sunlight is and through , and is obvious as when the Sun is above the . When direct is not blocked by s, it is experienced as sunshine, a combination of b ...

sunlight
into
electricity Electricity is the set of physical Physical may refer to: *Physical examination, a regular overall check-up with a doctor *Physical (album), ''Physical'' (album), a 1981 album by Olivia Newton-John **Physical (Olivia Newton-John song), "Physi ...

electricity
, either directly using
photovoltaics Photovoltaics (PV) is the conversion of light into electricity using semiconducting material A semiconductor material has an Electrical resistivity and conductivity, electrical conductivity value falling between that of a Electrical conduct ...
(PV), indirectly using
concentrated solar power Concentrated solar power (CSP, also known as concentrating solar power, concentrated solar thermal) systems generate solar power by using mirrors or lenses to concentrate a large area of sunlight onto a receiver. Electricity is generated whe ...
, or a combination. Concentrated solar power systems use
lenses A lens is a transmissive optics, optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a #Compound lenses, compound lens consists of several simple ...

lenses
or
mirrors A mirror is an object that reflects an image An image (from la, imago) is an artifact that depicts visual perception Visual perception is the ability to interpret the surrounding environment (biophysical), environment thro ...
and
solar tracking A solar tracker is a device that orients a payload toward the Sun. Payloads are usually solar panel A solar panel, or photo-voltaic (PV) module, is an assembly of photo-voltaic cells mounted in a framework for installation. Solar panels use ...
systems to focus a large area of sunlight into a small beam.
Photovoltaic cells A solar cell, or photovoltaic cell, is an electrical device that converts the energy of light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is visual perception, perceived b ...
convert light into an
electric current An electric current is a stream of charged particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, ...
using the
photovoltaic effect The photovoltaic effect is the generation of voltage and electric current An electric current is a stream of charged particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, ...
. Photovoltaics were initially solely used as a source of
electricity Electricity is the set of physical Physical may refer to: *Physical examination, a regular overall check-up with a doctor *Physical (album), ''Physical'' (album), a 1981 album by Olivia Newton-John **Physical (Olivia Newton-John song), "Physi ...

electricity
for small and medium-sized applications, from the
calculator An electronic calculator is typically a portable device used to perform s, ranging from basic to complex . The first calculator was created in the early 1960s. Pocket-sized devices became available in the 1970s, especially after the , the f ...

calculator
powered by a single solar cell to remote homes powered by an
off-grid Off-the-grid or off-grid is a characteristic of buildings and a lifestyle designed in an independent manner without reliance on one or more public utility, public utilities. The term "off-the-grid" traditionally refers to not being connected to ...
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 An electric power system is a network of electrical components deployed to supply, transfer, and use electric power. An example of a power system is the e ...
have grown more or less exponentially. Millions of installations and gigawatt-scale
photovoltaic power station A photovoltaic power station, also known as a solar park, solar farm, or solar power plant, is a large-scale grid-connected photovoltaic power system A grid-connected photovoltaic system, or grid-connected PV system is an electricity El ...
s have been and are being built. Solar PV has rapidly become an inexpensive, low-carbon technology. The
International Energy Agency The International Energy Agency (IEA; french: Agence internationale de l'énergie) is a Paris Paris () is the Capital city, capital and List of communes in France with over 20,000 inhabitants, most populous city of France, with an estima ...
said in 2021 that under its "Net Zero by 2050" scenario solar power would contribute about 20% of worldwide
energy consumption Energy consumption is the amount of energy In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order ...
, and solar would be the world's largest source of electricity. China has the most solar installations. In 2020, solar power generated 3.5% of the world's electricity, compared to under 3% the previous year. In 2020 the unsubsidised
levelised cost of electricity The levelized cost of energy (LCOE), or levelized cost of electricity, is a measure of the average net present cost of electricity generation for a generating plant over its lifetime. It is used for investment planning and to compare different me ...
for utility-scale solar power was around $36/MWh, and installation cost about a dollar per DC watt.


Mainstream technologies

Many industrialized nations have installed significant solar power capacity into their grids to supplement or provide an alternative to
conventional energy Energy development is the field of activities focused on obtaining sources of energy from natural resources. These activities include production of conventional, Alternative energy, alternative and Renewable energy, renewable sources of energy ...
sources while an increasing number of less developed nations have turned to solar to reduce dependence on expensive imported fuels ''(see
solar power by country Many countries and territories have installed significant solar power Solar power is the conversion of renewable energy Renewable energy is energy that is collected from renewable resource File:Global Vegetation.jpg, Global veget ...
)''. Long-distance transmission allows remote
renewable energy Renewable energy is energy that is collected from renewable resource File:Global Vegetation.jpg, Global vegetation A renewable resource, also known as a flow resource, is a natural resource which will replenish to replace the portion resou ...
resources to displace fossil fuel consumption. Solar power plants use one of two technologies: *
Photovoltaic Photovoltaics (PV) is the conversion of light into electricity using semiconducting material A semiconductor material has an Electrical resistivity and conductivity, electrical conductivity value falling between that of a Electrical conduct ...

Photovoltaic
(PV)
systems A system is a group of interacting Interaction is a kind of action that occurs as two or more objects have an effect upon one another. The idea of a two-way effect is essential in the concept of interaction, as opposed to a one-way causal ...
use
solar panel A solar cell panel, solar electric panel, photo-voltaic (PV) module or just solar panel is an assembly of photo-voltaic cells mounted in a framework for installation. Solar panels use sunlight Sunlight is a portion of the given off by ...

solar panel
s, either on rooftops or in ground-mounted
solar farm A photovoltaic power station, also known as a solar park, solar farm, or solar power plant, is a large-scale grid-connected photovoltaic power system A grid-connected photovoltaic system, or grid-connected PV system is an electricity El ...
s, converting sunlight directly into electric power. *
Concentrated solar power Concentrated solar power (CSP, also known as concentrating solar power, concentrated solar thermal) systems generate solar power by using mirrors or lenses to concentrate a large area of sunlight onto a receiver. Electricity is generated whe ...
(CSP, also known as "concentrated solar thermal") plants use
solar thermal energy Solar thermal energy (STE) is a form of energy and a technology for harnessing solar energy to generate thermal energy for use in Industrial sector, industry, and in the residential and commercial sectors. Solar thermal collectors are classifie ...
to make steam, which is thereafter converted into electricity by a turbine.


Photovoltaic cells

A
solar cell A solar cell, or photovoltaic cell, is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physics, physical and Chemical substance, chemical phenomenon.
, or photovoltaic cell (PV), is a device that converts light into electric current using the
photovoltaic effect The photovoltaic effect is the generation of voltage and electric current An electric current is a stream of charged particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, ...
. 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. Frit ...
in the 1880s. The German industrialist
Ernst Werner von Siemens Ernst Werner Siemens (von The term ''von'' () is used in German language The German language (, ) is a West Germanic language mainly spoken in Central Europe. It is the most widely spoken and official or co-official language in German ...

Ernst Werner von Siemens
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 Copper(I) oxide or cuprous oxide is the inorganic compound In chemistry, an inorganic compound is typically a chemical compound that ...
, although the prototype
selenium Selenium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that ...

selenium
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 engineer who is generally recognized for patenting the modern solar cell (, "Light sensitive device"). Ohl was a notable semiconductor researcher prior to the invention of ...
in the 1940s, researchers Gerald Pearson,
Calvin Fuller Calvin Souther Fuller (May 25, 1902 – October 28, 1994) was a physical chemist at AT&T Bell Laboratories where he worked for 37 years from 1930 to 1967. Fuller was part of a team in basic research that found answers to physical challenges. He ...
and Daryl Chapin created the
silicon Silicon is a chemical element with the Symbol (chemistry), symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a Tetravalence, tetravalent metalloid and semiconductor. It is a member ...

silicon
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, physical chemist Physical chemistry is the study of macroscopic The macroscopic scale is the length scale on which ...

Mohamed M. Atalla
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 Visual percep ...
by
thermal oxidation In microfabrication Microfabrication is the process of manufacturing, fabricating miniature structures of micrometre scales and smaller. Historically, the earliest microfabrication processes were used for integrated circuit fabrication, also known ...
at
Bell Labs Nokia Bell Labs (formerly named Bell Labs Innovations (1996–2007), AT&T Bell Laboratories (1984–1996) and Bell Telephone Laboratories (1925–1984)) is an American industrial research and scientific development company A company, ab ...
. 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 photovoltaic Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovol ...
. The array of a
photovoltaic power system
photovoltaic power system
, or PV system, produces
direct current Direct current (DC) is one-directional flow Flow may refer to: Science and technology * Flow (fluid) or fluid dynamics, the motion of a gas or liquid * Flow (geomorphology), a type of mass wasting or slope movement in geomorphology * Flow (math ...
(DC) power which fluctuates with the sunlight's intensity. For practical use this usually requires conversion to certain desired voltages or alternating current (AC), through the use of
inverters A power inverter, inverter or invertor is a power electronics, 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. In ...
. Multiple solar cells are connected inside modules. Modules 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 system A stand-alone power system (SAPS or SPS), also known as remote area power supply (RAPS), is an off-the-grid electricity system for locations that are not fitted with an electricity distribution system. Typical SAPS include one or more methods of e ...
s permit operations at night and at other times of limited sunlight.


Concentrated solar power

Concentrated solar power Concentrated solar power (CSP, also known as concentrating solar power, concentrated solar thermal) systems generate solar power by using mirrors or lenses to concentrate a large area of sunlight onto a receiver. Electricity is generated whe ...
(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 focus ...

parabolic trough
, the compact linear Fresnel reflector, the
dish Stirling Solar thermal energy (STE) is a form of energy and a technology Technology ("science of craft", from Ancient Greek, Greek , ''techne'', "art, skill, cunning of hand"; and , ''wikt:-logia, -logia'') is the sum of Art techniques and materials, ...
and the
solar power tower A solar power tower, also known as 'central tower' power plant or '' power plant, is a type of using a tower to receive focused sunlight. It uses an array of flat, movable mirrors (called heliostats) to focus the sun's rays upon a collector to ...
. Various techniques are used to track the sun and focus light. In all of these systems a
working fluid For fluid power Fluid power is the use of fluids under pressure to generate, control, and transmit power. Fluid power is subdivided into hydraulics using a liquid such as mineral oil or water Water is an Inorganic compound, inorgan ...
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 up to 24-hour electricity generation. A ''parabolic trough'' consists of a linear parabolic reflector that concentrates light onto a receiver positioned along the reflector's focal line. The receiver is a tube positioned along the focal points of the linear parabolic mirror and is filled with a working fluid. The reflector is made to follow the sun during daylight hours by tracking along a single axis. Parabolic trough systems provide the best land-use factor of any solar technology. The
Solar Energy Generating Systems Solar Energy Generating Systems (SEGS) is a concentrated solar power plant in California, United States. With the combined capacity from three separate locations at 354 megawatt (MW), it is the world's List of solar thermal power stations, second ...
plants in California and Acciona's
Nevada Solar One Nevada Solar One is a concentrated solar power plant, with a nominal capacity of 64 Watt, MW and maximum steam turbine power output up to 72 MW net (75 MW gross), spread over an area of . The projected Carbon dioxide, CO2 emissions a ...

Nevada Solar One
near
Boulder City, Nevada Boulder City is a town in Clark County, Nevada, United States. It is approximately southeast of Las Vegas. As of the 2010 United States Census, 2010 census, the population of Boulder City was 15,023. The town took its name from Boulder Canyon ( ...
are representatives of this technology. ''Compact Linear Fresnel Reflectors'' are CSP-plants which use many thin mirror strips instead of parabolic mirrors to concentrate sunlight onto two tubes with working fluid. This has the advantage that flat mirrors can be used which are much cheaper than parabolic mirrors, and that more reflectors can be placed in the same amount of space, allowing more of the available sunlight to be used. Concentrating linear fresnel reflectors can be used in either large or more compact plants. The ''Stirling solar dish'' combines a parabolic concentrating dish with a
Stirling engine File:Stirling Animation.gif, 136px, upBeta-type Stirling engine, with only one cylinder, hot at one end and cold at the other. A loose-fitting displacer shunts the air between the hot and cold ends of the cylinder. A power piston at the open end ...

Stirling engine
which normally drives an electric generator. The advantages of Stirling solar over photovoltaic cells are higher efficiency of converting sunlight into electricity and longer lifetime. Parabolic dish systems give the highest efficiency among CSP technologies. The 50 kW Big Dish in
Canberra Canberra ( ) is the capital city A capital or capital city is the holding primary status in a , , , , or other , usually as its seat of the government. A capital is typically a that physically encompasses the government's offices an ...

Canberra
, Australia is an example of this technology. A ''solar power tower'' uses an array of tracking reflectors (
heliostat experimental station in France. The mirror rotates on an altazimuth mount. Solar thermal energy, solar-thermal power project near Daggett, California. Every mirror in the field of heliostats reflects sunlight continuously onto the receiver on ...

heliostat
s) to concentrate light on a central receiver atop a tower. Power towers can achieve higher (thermal-to-electricity conversion) efficiency than linear tracking CSP schemes and better energy storage capability than dish stirling technologies. The
PS10 Solar Power Plant The PS10 Solar Power Plant ( es, Planta Solar 10), is the world's first commercial concentrating solar power tower A solar power tower, also known as 'central tower' power plant or '' power plant, is a type of using a tower to receive focuse ...
and
PS20 solar power plant The PS20 solar power plant (PS20) solar power plant is a solar thermal energy Solar thermal energy (STE) is a form of energy and a technology for harnessing solar energy to generate thermal energy for use in Industrial sector, industry, and in ...
are examples of this technology.


Hybrid systems

A hybrid system combines (C)PV and CSP with one another or with other forms of generation such as diesel, wind and
biogas Biogas is the mixture of gas Gas is one of the four fundamental states of matter In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and ...

biogas
. The combined form of generation may enable the system to modulate power output as a function of demand or at least reduce the fluctuating nature of solar power and the consumption of non-renewable fuel. Hybrid systems are most often found on islands. ; CPV/CSP system : A novel solar CPV/CSP hybrid system has been proposed, combining concentrator photovoltaics with the non-PV technology of concentrated solar power, or also known as concentrated solar thermal. ; Integrated solar combined cycle (ISCC) system : The Hassi R'Mel power station in Algeria is an example of combining CSP with a gas turbine, where a 25-megawatt CSP-
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 focus ...

parabolic trough
array supplements a much larger 130 MW
combined cycle A combined cycle power plant is an assembly of heat engine In thermodynamics and engineering, a heat engine is a system that converts heat to mechanical energy, which can then be used to do work (physics), mechanical work. It does this by ...
gas turbine plant. Another example is the Yazd power station in Iran. ;
Photovoltaic thermal hybrid solar collector Photovoltaic thermal collectors, typically abbreviated as PVT collectors and also known as hybrid solar collectors, photovoltaic thermal solar collectors, PV/T collectors or solar cogeneration Cogeneration or combined heat and power (CHP) is th ...
(PVT) : Also known as hybrid PV/T, convert solar radiation into thermal and electrical energy. Such a system combines a solar (PV) module with a
solar thermal collector A solar thermal collector collects heat by Absorption (optics), absorbing sunlight. The term "solar collector" commonly refers to a device for solar hot water panel, solar hot water heating, but may refer to large power generating installations ...
in a complementary way. ; Concentrated photovoltaics and thermal (CPVT) : A concentrated photovoltaic thermal hybrid system is similar to a PVT system. It uses
concentrated photovoltaic Concentrator photovoltaics (CPV) (also known as concentration photovoltaics) is a photovoltaic Photovoltaics (PV) is the conversion of light into electricity using semiconducting material A semiconductor material has an Electrical resis ...
s (CPV) instead of conventional PV technology, and combines it with a solar thermal collector. ;
PV diesel system Hybrid power are combinations between different technologies to produce power. Variability of renewable source like solar and wind remains a major concern, despite a substantial decrease in the capital cost of their power conversion devices. One ...
: It combines a photovoltaic system with a
diesel generator A diesel generator (DG) (also known as diesel genset) is the combination of a diesel engine The diesel engine, named after Rudolf Diesel Rudolf Christian Karl Diesel ( (); 18 March 1858 – 29 September 1913) was a German inventor and ...

diesel generator
. Combinations with other renewables are possible and include
wind turbine A wind turbine is a device that converts Religious conversion is the adoption of a set of beliefs identified with one particular religious denomination A religious denomination is a subgroup within a religion Religion is a social ...

wind turbine
s. ; PV-
thermoelectric The thermoelectric effect is the direct conversion of temperature Temperature is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy, present in all matter, which is the source of the occurrence of ...
system : Thermoelectric, or "thermovoltaic" devices convert a temperature difference between dissimilar materials into an electric current. Solar cells use only the high frequency part of the radiation, while the low frequency heat energy is wasted. Several patents about the use of thermoelectric devices in tandem with solar cells have been filed. The idea is to increase the efficiency of the combined solar/thermoelectric system to convert the solar radiation into useful electricity.


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. Frit ...
installed the world's first rooftop photovoltaic solar array, using 1%-efficient
selenium Selenium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that ...

selenium
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 and oil, is a naturally occurring, yellowish-black liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric process, isoc ...

petroleum
. 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. The 1973 oil embargo and
1979 energy crisis The 1979 Oil Crisis, also known as the 1979 Oil Shock or Second Oil Crisis, was an energy crisis An energy crisis is any significant bottleneck in the supply of energy In physics Physics (from grc, φυσική (ἐπιστ ...
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 Research and development (R&D, R+D), known in Europe as research and technological development (RTD), is the set of innovative activi ...

NREL
), Japan ( NEDO), and Germany ( Fraunhofer ISE). Between 1970 and 1983 installations of photovoltaic systems grew rapidly, but falling oil prices in the early 1980s moderated the
growth of photovoltaics Worldwide growth of photovoltaics has been close to exponential Exponential may refer to any of several mathematical topics related to exponentiation Exponentiation is a mathematical operation, written as , involving two numbers, the '' ...
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 Electricity is the set of physical Physical may refer to: *Physical examination, a regular overall check-up with a doctor *Physical ...
as well as utility-scale
photovoltaic power station A photovoltaic power station, also known as a solar park, solar farm, or solar power plant, is a large-scale grid-connected photovoltaic power system A grid-connected photovoltaic system, or grid-connected PV system is an electricity El ...
s began to accelerate again due to supply issues with oil and natural gas, global warming 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 has since shifted to Asia, especially
China China (), officially the People's Republic of China (PRC; ), is a country in East Asia East Asia is the eastern region of Asia Asia () is Earth's largest and most populous continent, located primarily in the Eastern Hemisphere ...
and
Japan Japan ( ja, 日本, or , and formally ) is an island country An island country or an island nation is a country A country is a distinct territory, territorial body or political entity. It is often referred to as the land of an in ...
, and to a growing number of countries and regions all over the world, including, but not limited to,
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
,
Canada Canada is a country in the northern part of North America North America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, ...
,
Chile Chile, officially the Republic of Chile, is a country in the western part of South America South America is a entirely in the and mostly in the , with a relatively small portion in the . It can also be described as the southern ...
,
India India, officially the Republic of India (Hindi Hindi (Devanagari: , हिंदी, ISO 15919, ISO: ), or more precisely Modern Standard Hindi (Devanagari: , ISO 15919, ISO: ), is an Indo-Aryan language spoken chiefly in Hindi Belt, ...
,
Israel Israel (; he, יִשְׂרָאֵל, translit=Yīsrāʾēl; ar, إِسْرَائِيل, translit=ʾIsrāʾīl), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a ...
,
Mexico Mexico, officially the United Mexican States, is a country A country is a distinct territorial body or political entity A polity is an identifiable political entity—any group of people who have a collective identity, who are organi ...
,
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. With over 60 million people, it is the world's 23rd-most populous nation and covers an area of . South Africa has three capital citie ...
,
South Korea South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korea, Korean Peninsula and sharing a Korean Demilitarized Zone, land border with North Korea. Its western border is for ...
,
Thailand Thailand ( th, ประเทศไทย), historically known as Siam, () officially the Kingdom of Thailand, is a country in Southeast Asia. It is located at the centre of the Mainland Southeast Asia, Indochinese Peninsula, spanning , wi ...
, 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 Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
. In 2012,
Tokelau Tokelau (; "north-northeast"; known previously as the Union Islands, and, until 1976, known officially as the Tokelau Islands) is a dependent territory A dependent territory, dependent area, or dependency (sometimes referred as an external ...

Tokelau
became the first country to be powered entirely by photovoltaic cells, with a 1 MW system using batteries for nighttime power. Worldwide growth of photovoltaics has averaged 40% per year from 2000 to 2013 and total installed capacity reached 303 GW at the end of 2016 with
China China (), officially the People's Republic of China (PRC; ), is a country in East Asia East Asia is the eastern region of Asia Asia () is Earth's largest and most populous continent, located primarily in the Eastern Hemisphere ...
having the most cumulative installations (78 GW) and
Honduras Honduras, officially the Republic of Honduras, is a country in Central America. The republic of Honduras is bordered to the west by Guatemala, to the southwest by El Salvador, to the southeast by Nicaragua, to the south by the Pacific Ocean ...
having the highest theoretical percentage of annual electricity usage which could be generated by solar PV (12.5%). The largest manufacturers are located in China. Concentrated solar power (CSP) also started to grow rapidly, increasing its capacity nearly tenfold from 2004 to 2013, albeit from a lower level and involving fewer countries than solar PV. As of the end of 2013, worldwide cumulative CSP-capacity reached 3,425 MW.


Current status

About half of installed capacity is utility scale.


Forecasts

Most new renewable capacity between 2021 and 2026 is forecast to be solar. 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 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 The Ivanpah Solar Electric Generating System is a concentrated solar thermal plant in the Mojave Desert. It is located at the base of Clark Mountain (California), Clark Mountain in California, across the state line from Primm, Nevada. The plant h ...

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 CSP may refer to: Education * College Student Personnel, an academic discipline * Commonwealth Supported Place, a category in Australian education * Concordia University (Saint Paul, Minnesota), US ...

Solnova Solar Power Station
(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 Sol ...
(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 syste ...
(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.


Current installation prices

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 Solar irradiance is the power Power typically refers to: * Power (physics) In physics, power is the amount of energy transferred or converted per unit time. In the International System of Units, the unit of power is the watt, equal to one j ...
, which varies through the day and year and is influenced by
latitude In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and planets. The first person to use the ...

latitude
and
climate Climate is the long-term pattern of weather Weather is the state of the atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a la ...

climate
. PV system output power also depends on ambient temperature, wind speed, solar spectrum, the local soiling conditions, and other factors. 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 th ...

Northern Africa
,
Southern Africa Southern Africa is the south South is one of the cardinal directions or compass points. South is the opposite of north and is perpendicular to the east and west. Etymology The word ''south'' comes from Old English ''sūþ'', from earlier Pr ...
,
Southwest Asia Western Asia, West Asia, or Southwest Asia, is the westernmost subregion A subregion is a part of a larger region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to t ...
,
Middle East The Middle East ( ar, الشرق الأوسط, ISO 233 The international standard An international standard is a technical standard A technical standard is an established norm (social), norm or requirement for a repeatable technical task whi ...

Middle East
, and
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

Australia
, as well as the much smaller deserts of
North North is one of the four compass points The points of the compass are the vectors by which planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydro ...

North
and
South America South America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continent ...

South America
. Africa's eastern
Sahara Desert The Sahara (, ; ar, الصحراء الكبرى, ', 'the Greatest Desert') is a desert on the . With an area of , it is the largest hot in the world and the third largest desert overall, smaller only than the deserts of and the northern . ...

Sahara Desert
, also known as the
Libyan Desert The Libyan Desert (not to be confused with the Libyan Sahara) is a geographical region filling the north-eastern  Sahara Desert, from eastern Libya to the Western Desert of Egypt and far northwestern Sudan. On medieval maps, its use predates ...
, has been observed to be the sunniest place on Earth according to NASA. Different measurements of
solar irradiance Solar irradiance is the power Power typically refers to: * Power (physics) In physics, power is the amount of energy transferred or converted per unit time. In the International System of Units, the unit of power is the watt, equal to one j ...
(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


Levelized cost of electricity

The PV industry has adopted
levelized cost of electricity The levelized cost of energy (LCOE), or levelized cost of electricity, is a measure of the average net present cost of electricity generation for a generating plant over its lifetime. It is used for investment planning and to compare different me ...
(LCOE) as the unit of cost. The electrical energy generated is sold in units of
kilowatt-hour The kilowatt-hour ( SI symbol: kW⋅h or kW h; commonly written as kWh) is a unit Unit may refer to: Arts and entertainment * UNIT Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fictio ...
s (kWh). As a rule of thumb, and depending on the local
insolation Solar irradiance is the power Power typically refers to: * Power (physics) In physics, power is the amount of energy transferred or converted per unit time. In the International System of Units, the unit of power is the watt, equal to one j ...

insolation
, 1 watt-peak of installed solar PV capacity generates about 1 to 2 kWh of electricity per year. This corresponds to a
capacity factor The net capacity factor is the unitless In dimensional analysis, a dimensionless quantity is a quantity to which no physical dimension is assigned, also known as a bare, pure, or scalar quantity or a quantity of dimension one, with a correspondin ...
of around 10–20%. The product of the local cost of electricity and the insolation determines the break-even point for solar power. The International Conference on Solar Photovoltaic Investments, organized by
EPIA VIA EPIA ('' VIA Embedded Platform Innovative Architecture'') is a series of mini-ITX Mini-ITX is a motherboard A motherboard (also called mainboard, main circuit board, system board, baseboard, planar board, logic board, or mobo) is the mai ...
, has estimated that PV systems will pay back their investors in 8 to 12 years. As a result, since 2006 it has been economical for investors to install photovoltaics for free in return for a long term
power purchase agreement A power purchase agreement (PPA), or electricity power agreement, is a contract between two parties, one which generates electricity (the seller) and one which is looking to purchase electricity (the buyer). The PPA defines all of the commercial te ...
. Fifty percent of commercial systems in the United States were installed in this manner in 2007 and over 90% by 2009. Shi Zhengrong has said that, as of 2012, unsubsidised solar power was already competitive with fossil fuels in India, Hawaii, Italy and Spain. He said "We are at a tipping point. No longer are renewable power sources like solar and wind a luxury of the rich. They are now starting to compete in the real world without subsidies". "Solar power will be able to compete without subsidies against conventional power sources in half the world by 2015".
Palo Alto Palo Alto (; for "tall stick") is a located in the northwestern corner of , United States, in the . The city is named after a known as . The city was established by when he founded , following the death of his son, Palo Alto includes port ...
California signed a wholesale purchase agreement in 2016 that secured solar power for 3.7 cents per kilowatt-hour. And in sunny
Dubai Dubai ( ; ar, دبي, translit=Dubayy , ) is the most populous city in the United Arab Emirates The United Arab Emirates (UAE; ar, الإمارات العربية المتحدة ) or the Emirates ( ar, الإمارات ), is a country i ...

Dubai
large-scale solar generated electricity sold in 2016 for just 2.99 cents per kilowatt-hour – "competitive with any form of fossil-based electricity — and cheaper than most." In 2020, the UNDP project "Enhanced Rural Resilience in Yemen" (ERRY) -which uses community-owned solar microgrids- managed to cuts energy costs to just 2 cents per hour (whereas diesel-generated electricity costs 42 cents per hour). As of October 2020, the unsubsidised levelised cost of electricity for utility-scale solar power is around $36/MWh.


Grid parity

Grid parity is the point at which the cost of photovoltaic electricity is equal to or cheaper than the price of grid power. This is more easily achieved in areas with abundant sun and high costs for electricity such as in
California California is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper), a daily newspaper i ...

California
and
Japan Japan ( ja, 日本, or , and formally ) is an island country An island country or an island nation is a country A country is a distinct territory, territorial body or political entity. It is often referred to as the land of an in ...

Japan
. In 2008, the levelized cost of electricity for solar PV was $0.25/kWh or less in most of the
OECD The Organisation for Economic Co-operation and Development (OECD; french: Organisation de Coopération et de Développement Économiques, OCDE) is an intergovernmental economic organisation with 38 member countries, founded in 1961 to st ...

OECD
countries. By late 2011, the fully loaded cost was predicted to fall below $0.15/kWh for most of the
OECD The Organisation for Economic Co-operation and Development (OECD; french: Organisation de Coopération et de Développement Économiques, OCDE) is an intergovernmental economic organisation with 38 member countries, founded in 1961 to st ...

OECD
and to reach $0.10/kWh in sunnier regions. These cost levels are driving three emerging trends: vertical integration of the supply chain, origination of
power purchase agreement A power purchase agreement (PPA), or electricity power agreement, is a contract between two parties, one which generates electricity (the seller) and one which is looking to purchase electricity (the buyer). The PPA defines all of the commercial te ...
s (PPAs) by solar power companies, and unexpected risk for traditional power generation companies, grid operators and wind turbine manufacturers. Grid parity was first reached in
Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = , national_anthem = , image_map = , map_caption = , image_map2 ...

Spain
in 2013,
Hawaii Hawaii ( ; haw, Hawaii or ) is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspape ...

Hawaii
and other islands that otherwise use
fossil fuel A fossil fuel is a hydrocarbon In , a hydrocarbon is an consisting entirely of and . Hydrocarbons are examples of s. Hydrocarbons are generally colourless and hydrophobic with only weak odours. Because of their diverse molecular structure ...
(
diesel fuel Diesel fuel in general is any liquid fuel Liquid fuels are combustible or energy-generating molecules that can be harnessed to create mechanical energy In physical sciences Physical science is a branch of natural science that studies abi ...
) to produce electricity, and most of the US is expected to reach grid parity by 2015. By 2020, grid parity was found over large areas, with the LCOE of utility PV power falling as low as $0.039 to $0.042 per kWh, compared to
combined cycle power plant A combined cycle power plant is an assembly of heat engine In thermodynamics and engineering, a heat engine is a system that converts heat to mechanical energy, which can then be used to do work (physics), mechanical work. It does this by ...
s $0.044 to $0.073 per kWh.


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 tank A hot water storage tank (also called a hot water tank, thermal storage tank, hot water thermal storage unit, heat storage tank and hot water cylinder) is a water tank used for storing hot water for space heating or domestic use. Water is a con ...
s 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 and incentives

The political purpose of incentive policies for PV is to facilitate an initial small-scale deployment to begin to grow the industry, even where the cost of PV is significantly above grid parity, to allow the industry to achieve the economies of scale necessary to reach grid parity. The 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)


Rebates

With investment subsidies, the financial burden falls upon the taxpayer, while with feed-in tariffs the extra cost is distributed across the utilities' customer bases. While the investment subsidy may be simpler to administer, the main argument in favour of feed-in tariffs is the encouragement of quality. Investment subsidies are paid out as a function of the nameplate capacity of the installed system and are independent of its actual power yield over time, thus rewarding the overstatement of power and tolerating poor durability and maintenance. Some electric companies offer rebates to their customers, such as
Austin Energy Austin Energy is a publicly owned utility providing Electric power, electrical power to the city of Austin, Texas and surrounding areas. Established in 1895, the utility is a department of the City of Austin and returns its profits to the city's ...
in
Texas Texas (, ; Spanish Spanish may refer to: * Items from or related to Spain: **Spaniards, a nation and ethnic group indigenous to Spain **Spanish language **Spanish cuisine Other places * Spanish, Ontario, Canada * Spanish River (disambigu ...

Texas
, which offers $2.50/watt installed up to $15,000.


Net metering

In
net metering Net metering (or net energy metering, NEM) is an electricity billing mechanism that allows consumers who generate some or all of their own electricity to use that electricity anytime, instead of when it is generated. This is particularly importan ...
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 meter North American domestic analog electricity meter. Electricity meter with transparent plastic case (Israel) North American domestic electronic electricity meter An electricity meter, electric meter, electrical meter, energy meter, or kilowat ...
s, which accurately measure power in both directions and automatically report the difference, and because it allows homeowners and businesses to generate electricity at a different time from consumption, effectively using the grid as a giant storage battery. With net metering, deficits are billed each month while surpluses are rolled over to the following month. Best practices call for perpetual roll over of kWh credits. 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. In New Jersey, annual excess credits are paid at the wholesale rate, as are left over credits when a customer terminates service.


Feed-in tariffs (FIT)

With
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, the financial burden falls upon the consumer. They reward the number of kilowatt-hours produced over a long period of time, but because the rate is set by the authorities, it may result in perceived overpayment. The price paid per kilowatt-hour under a feed-in tariff exceeds the price of grid electricity. Net metering refers to the case where the price paid by the utility is the same as the price charged. The complexity of approvals in California, Spain and Italy has prevented comparable growth to Germany even though the return on investment is better. In some countries, additional incentives are offered for
building-integrated photovoltaics Building-integrated photovoltaics (BIPV) are photovoltaic materials that are used to replace conventional building materials in parts of the building envelope such as the roof, skylights, or facades. They are increasingly being incorporated i ...
(BIPV) compared to stand alone PV: * France + EUR 0.16 /kWh (compared to semi-integrated) or + EUR 0.27/kWh (compared to stand alone) * Italy + EUR 0.04–0.09 kWh * Germany + EUR 0.05/kWh (facades only)


Solar Renewable Energy Credits (SRECs)

Alternatively,
Solar Renewable Energy Certificate Solar Renewable Energy Certificates (SRECs) or Solar Renewable Energy Credits are a form of Renewable Energy Certificates (United States), Renewable Energy Certificate or "Green tag" existing in the United States of America. SRECs exist in states ...
s (SRECs) allow for a market mechanism to set the price of the solar-generated electricity subsidy. In this mechanism, renewable energy production or consumption target is set, and the utility (more technically the Load Serving Entity) is obliged to purchase renewable energy or face a fine (Alternative Compliance Payment or ACP). The producer is credited for an SREC for every 1,000 kWh of electricity produced. If the utility buys this SREC and retires it, they avoid paying the ACP. In principle, this system delivers the cheapest renewable energy since all solar facilities are eligible and can be installed in most economic locations. Uncertainties about the future value of SRECs have led to long-term SREC contract markets to give clarity to their prices and allow solar developers to pre-sell and hedge their credits. Financial incentives for photovoltaics differ across countries, including
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
,
China China (), officially the People's Republic of China (PRC; ), is a country in East Asia East Asia is the eastern region of Asia Asia () is Earth's largest and most populous continent, located primarily in the Eastern Hemisphere ...
,
Germany ) , image_map = , map_caption = , map_width = 250px , capital = Berlin Berlin (; ) is the Capital city, capital and List of cities in Germany by population, largest city of Germany by both area and population. Its 3,769,495 inh ...
,
Israel Israel (; he, יִשְׂרָאֵל, translit=Yīsrāʾēl; ar, إِسْرَائِيل, translit=ʾIsrāʾīl), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a ...
,
Japan Japan ( ja, 日本, or , and formally ) is an island country An island country or an island nation is a country A country is a distinct territory, territorial body or political entity. It is often referred to as the land of an in ...
, 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 Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
and even across states within the US. The
Japanese government The is the central government of Japan , image_flag = Flag of Japan.svg , alt_flag = Centered deep red circle on a white rectangle , image_coat = Imperial Seal of Japan.svg , alt ...
through its
Ministry of International Trade and Industry The was a Ministry (government department), ministry of the Government of Japan from 1949 to 2001. The MITI was one of the most powerful government agencies in Japan and, at the height of its influence, effectively ran much of Japanese industri ...
ran a successful programme of subsidies from 1994 to 2003. By the end of 2004, Japan led the world in installed PV capacity with over 1.1  GW. In 2004, the
German government The Federal Cabinet or Federal Government (german: Bundeskabinett or ') is the chief executive body Executive may refer to: Role, title, or function * Executive (government) The executive is the branch of government A government is ...
introduced the first large-scale feed-in tariff system, under the
German Renewable Energy Act The Renewable Energy Sources Act or EEG (german: Erneuerbare-Energien-Gesetz) is a series of Germany, German laws that originally provided a feed-in tariff (FIT) scheme to encourage the generation of renewable electricity. The specified the ...
, which resulted in an explosive growth of PV installations in Germany. At the outset, the FIT was over 3x the retail price or 8x the industrial price. The principle behind the German system is a 20-year flat rate contract. The value of new contracts is programmed to decrease each year, in order to encourage the industry to pass on lower costs to the end-users. The programme has been more successful than expected with over 1GW installed in 2006, and political pressure is mounting to decrease the tariff to lessen the future burden on consumers. Subsequently,
Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = , national_anthem = , image_map = , map_caption = , image_map2 ...
,
Italy Italy ( it, Italia ), officially the Italian Republic ( it, Repubblica Italiana, links=no ), is a country consisting of a peninsula delimited by the Alps The Alps ; german: Alpen ; it, Alpi ; rm, Alps; sl, Alpe ) are the highest ...
,
Greece Greece ( el, Ελλάδα, Elláda, ), officially the Hellenic Republic, is a country located in Southeastern Europe Southeast Europe or Southeastern Europe () is a geographical subregion A subregion is a part of a larger region In geogr ...
—that enjoyed an early success with domestic solar-thermal installations for hot water needs—and
France France (), officially the French Republic (french: link=no, République française), is a transcontinental country This is a list of countries located on more than one continent A continent is one of several large landmasses ...
introduced feed-in tariffs. None has replicated the programmed decrease of FIT in new contracts though, making the German incentive relatively less and less attractive compared to other countries. California, Greece, France and Italy have 30–50% more insolation than Germany, making them financially more attractive.


Grid integration

The overwhelming majority of electricity produced worldwide is used immediately since storage is usually more expensive and because traditional generators can adapt to demand. Both solar power and
wind power Wind power or wind energy is the use of wind turbine A wind turbine is a device that converts Religious conversion is the adoption of a set of beliefs identified with one particular religious denomination A religious denomination ...

wind power
are
variable renewable energy Variable renewable energy (VRE) or intermittent renewable energy sources (IRES) are renewable energy Renewable energy is energy that is collected from renewable resource File:Global Vegetation.jpg, Global vegetation A renewable resource, ...
, meaning that all available output must be stored (e.g. in a battery) or taken whenever it is available by moving through
transmission Transmission may refer to: Science and technology * Power transmission ** Electric power transmission * Transmission (mechanics), a machine which provides controlled application of power * Transmission (telecommunications), the process of sending ...

transmission
lines to be used. 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 is where all energy use is sourced from renewable energy sources. The endeavor to use 100% renewable energy for electricity, heating/cooling and transport is motivated by climate change, pollution and other environmen ...
scenarios to have continuous electricity availability. Solar electricity is inherently variable and predictable by time of day, location, and seasons. In addition, 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 a summer peak utility, solar is well matched to daytime cooling demands. In utilities, solar displaces other forms of generation, reducing their
capacity factor The net capacity factor is the unitless In dimensional analysis, a dimensionless quantity is a quantity to which no physical dimension is assigned, also known as a bare, pure, or scalar quantity or a quantity of dimension one, with a correspondin ...
s. In an electricity system without
grid energy storage Grid energy storage (also called large-scale energy storage) is a collection of methods used for energy storage Energy storage is the capture of energy In physics, energy is the physical quantity, quantitative physical property, prop ...
, 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 Merit order, 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 betw ...
). 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 Energy storage is the capture of energy In physics, energy is the physical quantity, quantitative physical property, property that must be #Energy transfer, transferred to a physical body, body or physical system to perform Work (thermody ...
or
demand side management Energy demand management, also known as demand-side management (DSM) or demand-side response (DSR), is the modification of consumer energy demand, demand for energy through various methods such as financial incentives and behavioral change through ...
. Integrating large amounts of solar power with existing generation equipment has caused issues in some cases. For example, in Germany, California and Hawaii, electricity prices have been known to go negative when solar is generating a lot of power, displacing existing
baseload The baseload (also base load) on a grid is the minimum level of demand on an electrical grid An electrical grid is an interconnected network for electricity delivery from producers to consumers. Electrical grids vary in size and can cover who ...
generation contracts. Conventional hydroelectricity works very well in conjunction with solar power; water can be held back or released from a reservoir as required. Where a suitable river is not available,
pumped-storage hydroelectricity Pumped-storage hydroelectricity (PSH), or pumped hydroelectric energy storage (PHES), is a type of hydroelectric Hydroelectricity, or hydroelectric power, is electricity produced from hydropower Hydropower (from el, ὕδωρ, "wat ...
uses 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. This cycle can lose 20% of the energy to round trip inefficiencies, this plus the construction costs add to the expense of implementing high levels of solar power.
Concentrated solar power Concentrated solar power (CSP, also known as concentrating solar power, concentrated solar thermal) systems generate solar power by using mirrors or lenses to concentrate a large area of sunlight onto a receiver. Electricity is generated whe ...
plants may use
thermal storage Thermal energy storage (TES) is achieved with widely different technologies. Depending on the specific technology, it allows excess thermal energy to be stored and used hours, days, months later, at scales ranging from the individual process, b ...
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 The SOLAR Project consists of the Solar One, Solar Two and Solar Tres solar thermal energy, solar thermal power plants based in the Mojave Desert, United States and Andalucía, Spain. The US Department of Energy (DOE) and a consortium of US uti ...
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 Photovoltaic system#Standalone system, stand alone PV systems rechargeable batteries, batteries are traditionally used to store excess electricity. With grid-connected photovoltaic power system, 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. Credits are normally rolled over from month to month and any remaining surplus settled annually. 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. Battery storage, Batteries used for grid-storage can stabilize the electrical grid by Grid energy storage#Load leveling, leveling out peak loads for around an hour or more. 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, the valve regulated lead-acid battery– a modified version of the conventional lead–acid battery, nickel–cadmium battery, nickel–cadmium and Lithium-ion battery, lithium-ion batteries. Lead-acid batteries are currently the predominant technology used in small-scale, residential PV systems, due to their high reliability, low self-discharge and investment and maintenance costs, despite shorter lifetime and lower energy density. 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 provided by large production facilities such as the Gigafactory 1. In addition, the Li-ion batteries of plug-in electric cars may serve as future storage devices in a vehicle-to-grid system. Since most vehicles are parked an average of 95% of the time, their batteries could be used to let electricity flow from the car to the power lines and back. Other rechargeable batteries used for distributed energy storage system, distributed PV systems include, Sodium–sulfur battery, sodium–sulfur and Vanadium redox battery, vanadium redox batteries, two prominent types of a Molten salt battery, molten salt and a Flow battery, flow battery, respectively. 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 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. The Institute for Solar Energy Supply Technology of the University of Kassel pilot-tested a virtual power plant, combined power plant linking solar, wind,
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biogas
and
pumped-storage hydroelectricity Pumped-storage hydroelectricity (PSH), or pumped hydroelectric energy storage (PHES), is a type of hydroelectric Hydroelectricity, or hydroelectric power, is electricity produced from hydropower Hydropower (from el, ὕδωρ, "wat ...
to provide load-following power from renewable sources.


Environmental effects

Concentrated solar power may use much more water than gas-fired power. Unlike
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based technologies, solar power does not lead to any harmful emissions during operation, but the production of the panels leads to some amount of pollution.


Greenhouse gases

The life-cycle greenhouse-gas emissions of energy sources, life-cycle greenhouse-gas emissions of solar power are less than 50 gram (g) per
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(kWh).Alsema, E.A.; Wild – Scholten, M.J. de; Fthenakis, V.M.
Environmental impacts of PV electricity generation – a critical comparison of energy supply options
'' ECN, September 2006; 7p. Presented at the 21st European Photovoltaic Solar Energy Conference and Exhibition, Dresden, Germany, 4–8 September 2006.
Whereas (without carbon capture and storage) a
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gas-fired power plant emits around 500 g/kWh, and a coal-fired power plant about 1000 g/kWh. The most critical parameter is the solar insolation of the site: GHG emissions factors for PV solar are inversely proportional to insolation. 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.


Land use

Life-cycle surface power density of solar power is estimated at 6.63 W/m2 which is two Order of magnitude, orders of magnitude less than fossil fuels and nuclear power. Capacity factor of PV is also relatively low, usually below 15%. As result, 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 80% from PV by 2050 would require up to 2.8% of total landmass in European Union and up to 5% in countries like Japan and South Korea. Occupation of such large areas for PV farms would be likely to drive residential opposition as well as lead to deforestation, removal of vegetation and conversion of farm land. However these countries are very unlikely to need 80% from PV on their own land, as they have other low-carbon power such as offshore wind and may also import solar power from sparsely populated countries. Utility-scale photovoltaic farms use vast amount of space due to relatively low surface power density and occasionally face opposition from local residents, especially in countries with high population density or when the installation involves removal of existing trees or shrubs. Construction of Cleve Hill Solar Park in Kent (United Kingdom) composed of 880,000 panels up to 3.9 m high on 490 hectares of land faced opposition on the grounds of "destroying the local landscape". The solar farm divided Greenpeace (which opposed) and Friends of the Earth (which supported it). Similar concerns about deforestation were raised when large amounts of trees were removed for installation of solar farms in New Jersey and others.


Manufacturing and recycling

One issue that has often raised concerns is the use of cadmium (Cd), a toxic heavy metal that has the tendency to bioaccumulation, accumulate in ecological food chains. It is used as semiconductor component in cadmium telluride solar cell, CdTe solar cells and as a buffer layer for certain CIGS cells in the form of cadmium sulfide. The amount of cadmium used in thin-film solar cells is relatively small (5–10 g/m2) and with proper recycling and emission control techniques in place the cadmium emissions from module production can be almost zero. Current PV technologies lead to cadmium emissions of 0.3–0.9 microgram/kWh over the whole life-cycle. Most of these emissions arise through the use of coal power for the manufacturing of the modules, and coal and lignite combustion leads to much higher emissions of cadmium. Life-cycle cadmium emissions from coal is 3.1 microgram/kWh, lignite 6.2, and natural gas 0.2 microgram/kWh. In a life-cycle analysis it has been noted, that if electricity produced by photovoltaic panels were used to manufacture the modules instead of electricity from burning coal, cadmium emissions from coal power usage in the manufacturing process could be eliminated. In the case of crystalline silicon modules, the solder material, that joins the copper strings of the cells, contains about 36 percent of lead (Pb). Moreover, the paste used for screen printing front and back contacts contains traces of Pb and sometimes Cd as well. It is estimated that about 1,000 metric tonnes of Pb have been used for 100 gigawatts of c-Si solar modules. However, there is no fundamental need for lead in the solder alloy. Manufacturing of solar panels requires rare-earth elements, producing low-level radioactive waste during the mining process.
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study projects the demand for mined resources such as lithium, graphite, cobalt, copper, nickel and Rare-earth element, rare earths will rise 4x by 2040 and notes insufficient supply of these materials to match demand imposed by expected large-scale deployments of decentralized technologies solar and wind power, and required grid upgrades. According to a 2018 study significant increase of PV solar power would require 3000% increase in supply of these metals by 2060, thermal solar — 6000%, requiring significant increase in mining operations.


Political issues

Majority of the PV panels is manufactured in China using silicon sourced from one particular region of Xinjiang, which raises concerns about human rights violations (Xinjiang internment camps, Xinjang internment camps) as well as supply chain dependency.


Emerging technologies


Concentrator photovoltaics

Concentrator photovoltaics (CPV) systems employ sunlight concentrated onto photovoltaic surfaces for the purpose of electrical power production. Contrary to conventional photovoltaic systems, it uses Lens (optics), lenses and curved mirrors to focus sunlight onto small, but highly efficient, multi-junction solar cells. Solar concentrators of all varieties may be used, and these are often mounted on a solar tracker in order to keep the focal point upon the cell as the sun moves across the sky. Luminescent solar concentrators (when combined with a PV-solar cell) can also be regarded as a CPV system. Concentrated photovoltaics are useful as they can improve efficiency of PV-solar panels drastically. In addition, most solar panels on spacecraft are also made of high efficient multi-junction photovoltaic cells to derive electricity from sunlight when operating in the inner Solar System.


Floatovoltaics

Floatovoltaics are an emerging form of PV systems that float on the surface of irrigation canals, water reservoirs, quarry lakes, and tailing ponds. Several systems exist in France, India, Japan, Korea, the United Kingdom and the United States. These systems reduce the need of valuable land area, save drinking water that would otherwise be lost through evaporation, and show a higher efficiency of solar energy conversion, as the panels are kept at a cooler temperature than they would be on land. Although not floating, other dual-use facilities with solar power include Fishery, fisheries.


Solar updraft tower

The solar updraft tower (SUT) is a design concept for a Renewable energy, renewable-energy power plant for generating electricity from low temperature solar heat. Sunshine heats the air beneath a very wide greenhouse-like roofed collector structure surrounding the central base of a very tall chimney tower. The resulting convection causes a hot air updraft in the tower by the chimney effect. This airflow drives
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wind turbine
s, placed in the chimney updraft or around the chimney base, to produce
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electricity
. As of mid 2018, although several prototype models have been built, no full-scale practical units are in operation. Scaled-up versions of demonstration models are planned to generate significant power. They may also allow development of other applications, such as to agriculture or horticulture, to water extraction or distillation, or to improvement of urban air pollution


Perovskite solar cells


See also

*
100% renewable energy 100% renewable energy is where all energy use is sourced from renewable energy sources. The endeavor to use 100% renewable energy for electricity, heating/cooling and transport is motivated by climate change, pollution and other environmen ...
* Cost of electricity by source * Index of solar energy articles * List of cities by sunshine duration * List of energy storage projects * List of photovoltaic power stations * List of renewable energy organizations * List of solar thermal power stations * List of renewable energy topics by country * Renewable energy commercialization * Solar energy * Solar lamp * Solar vehicle * Sustainable energy * Timeline of solar cells


References


Further reading

*


External links

{{DEFAULTSORT:Solar Power Bright green environmentalism Solar power, Energy conversion Sustainable energy Sun, Power Renewable energy