Concentrated solar power

CSP had a global total installed capacity of 6,800 MW in 2021, up from 354 MW in 2005.[8] Spain accounted for almost one third of the world’s capacity, at 2,300 MW, despite no new capacity entering commercial operation in the country since 2013.[9] The United States follows with 1,740 MW. Interest is also notable in North Africa and the Middle East, as well as China and India. The global market was initially dominated by parabolic-trough plants, which accounted for 90% of CSP plants at one point.[10] Since about 2010, central power tower CSP has been favored in new plants due to its higher temperature operation – up to 565 °C (1,049 °F) vs. trough’s maximum of 400 °C (752 °F) – which promises greater efficiency.

Among the larger CSP projects are the Ivanpah Solar Power Facility (392 MW) in the United States, which uses solar power tower technology without thermal energy storage, and the Ouarzazate Solar Power Station in Morocco,[11] which combines trough and tower technologies for a total of 510 MW with several hours of energy storage.

As a thermal energy generating power station, CSP has more in common with thermal power stations such as coal, gas, or geothermal. A CSP plant can incorporate thermal energy storage, which stores energy either in the form of sensible heat or as latent heat (for example, using molten salt), which enables these plants to continue to generate electricity whenever it is needed, day or night. This makes CSP a dispatchable form of solar. Dispatchable renewable energy is particularly valuable in places where there is already a high penetration of photovoltaics (PV), such as California[12] because demand for electric power peaks near sunset just as PV capacity ramps down (a phenomenon referred to as duck curve).[13]

CSP is often compared to photovoltaic solar (PV) since they both use solar energy. While solar PV experienced huge growth in recent years due to falling prices,[14][15] Solar CSP growth has been slow due to technical difficulties and high prices. In 2017, CSP represented less than 2% of worldwide installed capacity of solar electricity plants.[16] However, CSP can more easily store energy during the night, making it more competitive with dispatchable generators and baseload plants.[17][18][19][20] The DEWA project in Dubai, under construction in 2019, held the world record for lowest CSP price in 2017 at US$73 per MWh[21] for its 700 MW combined trough and tower project: 600 MW of trough, 100 MW of tower with 15 hours of thermal energy storage daily. Base-load CSP tariff in the extremely dry Atacama region of Chile reached below $50/MWh in 2017 auctions.


A legend has it that Archimedes used a «burning glass» to concentrate sunlight on the invading Roman fleet and repel them from Syracuse. In 1973 a Greek scientist, Dr. Ioannis Sakkas, curious about whether Archimedes could really have destroyed the Roman fleet in 212 BC, lined up nearly 60 Greek sailors, each holding an oblong mirror tipped to catch the sun’s rays and direct them at a tar-covered plywood silhouette 49 m (160 ft) away. The ship caught fire after a few minutes; however, historians continue to doubt the Archimedes story.[24]

In 1866, Auguste Mouchout used a parabolic trough to produce steam for the first solar steam engine. The first patent for a solar collector was obtained by the Italian Alessandro Battaglia in Genoa, Italy, in 1886. Over the following years, inv?ntors such as John Ericsson and Frank Shuman developed concentrating solar-powered d?vices for irrigation, refrig?ration, and locom?tion. In 1913 Shuman finished a 55 horsepower (41 kW) parabolic solar thermal energy station in Maadi, Egypt for irrigation.[25][26][27][28] The first solar-power system using a mirror dish was built by Dr. R.H. Goddard, who was already well known for his research on liquid-fueled rockets and wrote an article in 1929 in which he asserted that all the previous obstacles had been addressed.[29]

Professor Giovanni Francia (1911–1980) designed and built the first concentrated-solar plant, which entered into operation in Sant’Ilario, near Genoa, Italy in 1968. This plant had the architecture of today’s power tower plants with a solar receiver in the center of a field of solar collectors. The plant was able to produce 1 MW with superheated steam at 100 bar and 500 °C.[30] The 10 MW Solar One power tower was developed in Southern California in 1981. Solar One was converted into Solar Two in 1995, implementing a new design with a molten salt mixture (60% sodium nitrate, 40% potassium nitrate) as the receiver working fluid and as a storage medium. The molten salt approach proved effective, and Solar Two operated successfully until it was decommissioned in 1999.[31] The parabolic-trough technology of the nearby Solar Energy Generating Systems (SEGS), begun in 1984, was more workable. The 354 MW SEGS was the largest solar power plant in the world, until 2014.

No commercial concentrated solar was constructed from 1990 when SEGS was completed until 2006 when the Compact linear Fresnel reflector system at Liddell Power Station in Australia was built. Few other plants were built with this design although the 5 MW Kimberlina Solar Thermal Energy Plant opened in 2009. In 2007, 75 MW Nevada Solar One was built, a trough design and the first large plant since SEGS. Between 2009 and 2013, Spain built over 40 parabolic trough systems, standardized in 50 MW blocks.

Parabolic trough

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 at the longitudinal focal line of the parabolic mirror and filled with a working fluid. The reflector follows the sun during the daylight hours by tracking along a single axis. A working fluid (e.g. molten salt[41]) is heated to 150–350 °C (302–662 °F) as it flows through the receiver and is then used as a heat source for a power generation system.[42] Trough systems are the most developed CSP technology. The Solar Energy Generating Systems (SEGS) plants in California, the world’s first commercial parabolic trough plants, Acciona’s Nevada Solar One near Boulder City, Nevada, and Andasol, Europe’s first commercial parabolic trough plant are representative, along with Plataforma Solar de Almería‘s SSPS-DCS test facilities in Spain.

Parabolic trough at a plant near Harper Lake, California

Enclosed trough

The design encapsulates the solar thermal system within a greenhouse-like glasshouse. The glasshouse creates a protected environment to withstand the elements that can negatively impact reliability and efficiency of the solar thermal system.[44] Lightweight curved solar-reflecting mirrors are suspended from the ceiling of the glasshouse by wires. A single-axis tracking system positions the mirrors to retrieve the optimal amount of sunlight. The mirrors concentrate the sunlight and focus it on a network of stationary steel pipes, also suspended from the glasshouse structure.[45] Water is carried throughout the length of the pipe, which is boiled to generate steam when intense solar radiation is applied. Sheltering the mirrors from the wind allows them to achieve higher temperature rates and prevents dust from building up on the mirrors.[44]

GlassPoint Solar, the company that created the Enclosed Trough design, states its technology can produce heat for Enhanced Oil Recovery (EOR) for about $5 per 290 kWh (1,000,000 BTU) in sunny regions, compared to between $10 and $12 for other conventional solar thermal technologies.

Solar thermal enhanced oil recovery

Heat from the sun can be used to provide steam used to make heavy oil less viscous and easier to pump. Solar power tower and parabolic troughs can be used to provide the steam which is used directly so no generators are required and no electricity is produced. Solar thermal enhanced oil recovery can extend the life of oilfields with very thick oil which would not otherwise be economical to pump.[57]

CSP with thermal energy storage

In a CSP plant that includes storage, the solar energy is first used to heat the molten salt or synthetic oil which is stored providing thermal/heat energy at high temperature in insulated tanks.[58][59] Later the hot molten salt (or oil) is used in a steam generator to produce steam to generate electricity by steam turbo generator as per requirement.[60] Thus solar energy which is available in daylight only is used to generate electricity round the clock on demand as a load following power plant or solar peaker plant.[61][62] The thermal storage capacity is indicated in hours of power generation at nameplate capacity. Unlike solar PV or CSP without storage, the power generation from solar thermal storage plants is dispatchable and self-sustainable similar to coal/gas-fired power plants, but without the pollution.[63] CSP with thermal energy storage plants can also be used as cogeneration plants to supply both electricity and process steam round the clock. As of December 2018, CSP with thermal energy storage plants generation cost have ranged between 5 c € / kWh and 7 c € / kWh depending on good to medium solar radiation received at a location.[64] Unlike solar PV plants, CSP with thermal energy storage plants can also be used economically round the clock to produce only process steam replacing pollution emitting fossil fuels. CSP plant can also be integrated with solar PV for better synergy.


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