Solar power

Solar power, also known as solar electricity, is the conversion of energy from sunlight into electricity, either directly using photovoltaics or indirectly using concentrated solar power. Solar panels use the photovoltaic effect to convert light into an electric current. Concentrated solar power systems use lenses or mirrors and solar tracking 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 panels has fallen, grid-connected solar PV systems' capacity and production have doubled about every three years. Three-quarters of new generation capacity is solar, with both millions of rooftop installations and gigawatt-scale photovoltaic power stations continuing to be built.
In 2024, solar power generated 7% of global electricity and over 1% of primary energy, adding twice as much new electricity as coal.
Along with onshore wind power, utility-scale solar is the source with the cheapest levelised cost of electricity for new installations in most countries. China has about half the world’s solar power. Almost half the solar power installed in 2022 was mounted on rooftops.
Much more low-carbon power is needed for electrification and to limit climate change. The International Energy Agency said in 2022 that more effort was needed for grid integration and the mitigation of policy, regulation and financing challenges. Nevertheless solar may greatly cut the cost of energy. Solar is important for energy security.

Potential

Geography affects solar energy potential because some places are sunnier than others. In particular areas that are closer to the equator generally receive more sunshine. However, solar panels that can follow the position of the Sun can significantly increase the solar energy potential in areas that are farther from the equator. Daytime cloud cover can reduce the light available for solar cells. Land availability also has a large effect on the available solar energy.

Technologies

Solar power plants use one of two technologies:

Photovoltaic systems use solar panels, either on rooftops or in ground-mounted solar farms, converting sunlight directly into electric power.
Concentrated solar power systems use mirrors or lenses to concentrate sunlight to extreme heat to make steam, which drives a turbine to generate electricity.
Solar cells

The photovoltaic effect in solar cells converts light into electric current. The first solar cell was constructed by Charles Fritts in the 1880s. The German industrialist 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 in place of copper oxide, although the prototype selenium cells converted less than 1% of incident light into electricity. Following the work of Russell Ohl in the 1940s, researchers Gerald Pearson, Calvin Fuller and Daryl Chapin created the 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 developed the process of silicon surface passivation by thermal oxidation at Bell Labs. The surface passivation process has since been critical to solar cell efficiency.
over 90% of the market is crystalline silicon. The array of a photovoltaic system, or PV system, produces direct current power which fluctuates with the sunlight's intensity. For practical use this usually requires conversion to alternating current, through the use of inverters. 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 when available, especially in developed countries with large markets. In these grid-connected PV systems 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.
In a "vertical agrivoltaics" system, solar cells are oriented vertically on farmland, to allow the land to both grow crops and generate renewable energy. Other configurations include floating solar farms, placing solar canopies over parking lots, and rooftop solar.

Thin-film solar

A thin-film solar cell is a second generation solar cell that is made by depositing one or more thin layers, or thin film of photovoltaic material on a substrate, such as glass, plastic or metal. Thin-film solar cells are commercially used in several technologies, including cadmium telluride, copper indium gallium diselenide, and amorphous thin-film silicon.

Perovskite solar cells

Concentrated solar power

, also called "concentrated solar thermal", uses lenses or mirrors and tracking systems to concentrate sunlight, then uses the resulting heat to generate electricity from conventional steam-driven turbines.
the levelized cost of electricity from CSP is over twice that of PV. As of 2022, less than 1% of solar power comes from CSP.

Hybrid systems

A hybrid system combines solar with energy storage 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 much 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 installed the world's first rooftop photovoltaic solar array, using 1%-efficient 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. Bell Telephone Laboratories' 1950s research used silicon wafers with a thin coating of boron. The "Bell Solar Battery" was described as 6% efficient, with a square yard of the panels generating 50 watts. The first satellite with solar panels was launched in 1957.
By the 1970s, solar panels were still too expensive for much other than satellites. 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 and 1979 energy crisis 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, Japan, and Germany. Between 1970 and 1983 installations of photovoltaic systems grew rapidly. In the United States, President Jimmy Carter set a target of producing 20% of U.S. energy from solar by the year 2000, but his successor, Ronald Reagan, removed the funding for research into renewables. Falling oil prices in the early 1980s moderated the growth of photovoltaics from 1984 to 1996.

Mid-1990s to 2010

In the mid-1990s development of both residential and commercial rooftop solar, as well as utility-scale photovoltaic power stations, began to accelerate again due to supply issues with oil and natural gas, global warming concerns, and the improving economics of PV relative to other energy technologies. In the early 2000s, the adoption of feed-in tariffs—a policy mechanism that gives renewables priority on the grid and defines a fixed price for the generated electricity—led to a high level of investment security and to a soaring number of PV deployments in Europe.

2010s

For several years, worldwide growth of solar PV was driven by European deployment, but it then shifted to Asia, especially China and Japan, and to a growing number of countries and regions all over the world. Chinese manufacturers of solar equipment grew to be the largest. Although concentrated solar power capacity grew more than tenfold, it remained a tiny proportion of the total, because the cost of utility-scale solar PV fell by 85% between 2010 and 2020, while CSP costs only fell 68% in the same timeframe.

2020s

Despite the rising cost of materials, such as polysilicon, during the 2021–2022 global energy crisis, utility scale solar was still the least expensive energy source in many countries due to the rising costs of other energy sources, such as natural gas. In 2022, global solar generation capacity exceeded 1 TW for the first time. However, fossil-fuel subsidies have slowed the growth of solar generation capacity.

Current status

About half of installed capacity is utility scale.

Forecasts

Solar is forecast to become the largest source of renewable power before the end of the 2020s, exceeding the output of hydropower. Utility scale is forecast to become the largest source of electricity in all regions except sub-Saharan Africa by 2050.

Photovoltaic power stations

Concentrating solar power stations

Commercial concentrating solar power 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 Andasol solar power station, and Extresol Solar Power Station, 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.