# Concentrated solar power

Not to be confused with concentrator photovoltaics.
The three towers of the Ivanpah Solar Power Facility.
Part of the 354 MW SEGS solar complex in northern San Bernardino County, California.

Concentrated solar power (also called concentrating solar power, concentrated solar thermal, and CSP) systems generate solar power by using mirrors or lenses to concentrate a large area of sunlight, or solar thermal energy, onto a small area. Electricity is generated when the concentrated light is converted to heat, which drives a heat engine (usually a steam turbine) connected to an electrical power generator [1][2][3] or powers a thermochemical reaction (experimental as of 2013).[4][5][6]

CSP is being widely commercialized and the CSP market saw about 740 megawatt (MW) of generating capacity added between 2007 and the end of 2010. More than half of this (about 478 MW) was installed during 2010, bringing the global total to 1095 MW. Spain added 400 MW in 2010, taking the global lead with a total of 632 MW, while the US ended the year with 509 MW after adding 78 MW, including two fossil–CSP hybrid plants.[7] The Middle East is also ramping up their plans to install CSP based projects and as a part of that Plan, Shams-I which was the largest CSP Project in the world has been installed in Abu Dhabi, by Masdar.[8] The largest CSP project in the world until January 2016 is Noor in Morocco[9] and global operational power stands at 4,705 MW.

There is considerable academic and commercial interest internationally in a new form of CSP, called STEM, for off-grid applications to produce 24-hour industrial scale power for mining sites and remote communities in Italy, other parts of Europe, Australia, Asia, North Africa and Latin America. STEM uses fluidized silica sand as a thermal storage and heat transfer medium for CSP systems. It has been developed by Salerno-based Magaldi Industries. The first commercial application of STEM was scheduled to take place in Sicily from 2015.[10]

CSP growth is expected to continue at a fast pace. As of January 2014, Spain had a total capacity of 2,300 MW making this country the world leader in CSP. United States follows with 1,740 MW. Interest is also notable in North Africa and the Middle East, as well as India and China. In Italy, a handful of companies are trying to get authorization for 14 plants, totalling 392 MW, despite a strong local and political opposition.[11] The global market has been dominated by parabolic-trough plants, which account for 90% of CSP plants.[7]

CSP is not to be confused with concentrator photovoltaics (CPV). In CPV, the concentrated sunlight is converted directly to electricity via the photovoltaic effect.

Ivanpah in California is running 69 percent below advertised power output, and one Spanish company, Abengoa, that commercialized CSP both in the US and abroad, is teetering on the brink of bankruptcy. CSP technologies currently cannot compete on price with photovoltaics (solar panels), which have experienced huge growth in recent years due to falling prices of the panels.[12] Another drawback of Ivanpah is that it lacks thermal energy storage, one of the big advantages that CSP has over PV and most other renewables, which require either large scale energy storage systems like pumped hydro or fast acting natural gas power plants to be there as backup for those times when they are not producing much energy.

## History

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 160 feet away. The ship caught fire after a few minutes; however, historians continue to doubt the Archimedes story.[13]

In 1866, Auguste Mouchout used a parabolic trough to producе 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, invеntors such as John Ericsson and Frank Shuman developed concentrating solar-powered dеvices for irrigation, refrigеration, and locomоtion. In 1913 Shuman finished a 55 HP parabolic solar thermal energy station in Maadi, Egypt for irrigation.[14][15][16][17] 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.[18]

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 concentrated-solar 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.[19] The 10 MW Solar One power tower was developed in Southern California in 1981, but the parabolic-trough technology of the nearby Solar Energy Generating Systems (SEGS), begun in 1984, was more workable. The 354 MW SEGS is still the largest solar power plant in the world, and will remain so until the 390 MW Ivanpah power tower project reaches full power.

## Current technology

CSP is used to produce electricity (sometimes called solar thermoelectricity, usually generated through steam). Concentrated-solar technology systems use mirrors or lenses with tracking systems to focus a large area of sunlight onto a small area. The concentrated light is then used as heat or as a heat source for a conventional power plant (solar thermoelectricity). The solar concentrators used in CSP systems can often also be used to provide industrial process heating or cooling, such as in solar air-conditioning.

Concentrating technologies exist in five common forms, namely parabolic trough, enclosed trough, dish Stirlings, concentrating linear Fresnel reflector, and solar power tower.[20] Although simple, these solar concentrators are quite far from the theoretical maximum concentration.[21][22] For example, the parabolic-trough concentration gives about ⅓ of the theoretical maximum for the design acceptance angle, that is, for the same overall tolerances for the system. Approaching the theoretical maximum may be achieved by using more elaborate concentrators based on nonimaging optics.[21][22][23]

Different types of concentrators produce different peak temperatures and correspondingly varying thermodynamic efficiencies, due to differences in the way that they track the sun and focus light. New innovations in CSP technology are leading systems to become more and more cost-effective.[24]

### Parabolic trough

Parabolic trough at a plant near Harper Lake, California
Main article: 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 directly above the middle 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[25]) is heated to 150–350 °C (300–660 °F) as it flows through the receiver and is then used as a heat source for a power generation system.[26] 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.[27]

#### Enclosed trough

Enclosed trough systems are used to absorb heat rather than process heat. 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.[28] 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.[29] 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.[28]

Inside an enclosed trough system

## Incentives

### Spain

Solar-thermal electricity generation is eligible for feed-in tariff payments (art. 2 RD 661/2007), if the system capacity does not exceed the following limits: Systems registered in the register of systems prior to 29 September 2008: 500 MW for solar-thermal systems. Systems registered after 29 September 2008 (PV only). The capacity limits for the different system types are re-defined during the review of the application conditions every quarter (art. 5 RD 1578/2008, Annex III RD 1578/2008). Prior to the end of an application period, the market caps specified for each system type are published on the website of the Ministry of Industry, Tourism and Trade (art. 5 RD 1578/2008).[52]

Since 27 January 2012, Spain has halted acceptance of new projects for the feed-in-tariff.[53][54] Projects currently accepted are not affected, except that a 6% tax on feed-in-tariffs has been adopted, effectively reducing the feed-in-tariff.[55]

### Australia

At the federal level, under the Large-scale Renewable Energy Target (LRET), in operation under the Renewable Energy Electricity Act 2000, large scale solar thermal electricity generation from accredited RET power stations may be entitled to create large-scale generation certificates (LGCs). These certificates can then be sold and transferred to liable entities (usually electricity retailers) to meet their obligations under this tradeable certificates scheme. However, as this legislation is technology neutral in its operation, it tends to favour more established RE technologies with a lower levelised cost of generation, such as large scale onshore wind, rather than solar thermal and CSP.[56] At State level, renewable energy feed-in laws typically are capped by maximum generation capacity in kWp, and are open only to micro or medium scale generation and in a number of instances are only open to solar PV (photovoltaic) generation. This means that larger scale CSP projects would not be eligible for payment for feed-in incentives in many of the State and Territory jurisdictions.

## Future

A study done by Greenpeace International, the European Solar Thermal Electricity Association, and the International Energy Agency's SolarPACES group investigated the potential and future of concentrated solar power. The study found that concentrated solar power could account for up to 25% of the world's energy needs by 2050. The increase in investment would be from 2 billion euros worldwide to 92.5 billion euros in that time period.[57] Spain is the leader in concentrated solar power technology, with more than 50 government-approved projects in the works. Also, it exports its technology, further increasing the technology's stake in energy worldwide. Because the technology works best with areas of high insolation (solar radiation), experts predict the biggest growth in places like Africa, Mexico, and the southwest United States. It indicates that the thermal storage systems based in nitrates (calcium, potassium, sodium,...) will make the CSP plants more and more profitable. The study examined three different outcomes for this technology: no increases in CSP technology, investment continuing as it has been in Spain and the US, and finally the true potential of CSP without any barriers on its growth. The findings of the third part are shown in the table below:

Year Annual
Investment
Cumulative
Capacity
2015 21 billion euros 420 megawatts
2050 174 billion euros 1,500,000 megawatts

Finally, the study acknowledged how technology for CSP was improving and how this would result in a drastic price decrease by 2050. It predicted a drop from the current range of €0.23–0.15/kwh to €0.14–0.10/kwh.[57] Recently the EU has begun to look into developing a €400 billion ($774 billion) network of solar power plants based in the Sahara region using CSP technology known as Desertec, to create "a new carbon-free network linking Europe, the Middle East and North Africa". The plan is backed mainly by German industrialists and predicts production of 15% of Europe's power by 2050. Morocco is a major partner in Desertec and as it has barely 1% of the electricity consumption of the EU, it will produce more than enough energy for the entire country with a large energy surplus to deliver to Europe.[58] Algeria has the biggest area of desert, and private Algerian firm Cevital has signed up for Desertec.[58] With its wide desert (the highest CSP potential in the Mediterranean and Middle East regions ~ about 170 TWh/year) and its strategic geographical location near Europe Algeria is one of the key countries to ensure the success of Desertec project. Moreover, with the abundant natural-gas reserve in the Algerian desert, this will strengthen the technical potential of Algeria in acquiring Solar-Gas Hybrid Power Plants for 24-hour electricity generation. Other organizations expect CSP to cost$0.06(US)/kWh by 2015 due to efficiency improvements and mass production of equipment.[59] That would make CSP as cheap as conventional power. Investors such as venture capitalist Vinod Khosla expect CSP to continuously reduce costs and actually be cheaper than coal power after 2015.

On 9 September 2009; 7 years ago, Bill Weihl, Google.org's green-energy spokesperson said that the firm was conducting research on the heliostat mirrors and gas turbine technology, which he expects will drop the cost of solar thermal electric power to less than \$0.05/kWh in 2 or 3 years.[47]

In 2009, scientists at the National Renewable Energy Laboratory (NREL) and SkyFuel teamed to develop large curved sheets of metal that have the potential to be 30% less expensive than today's best collectors of concentrated solar power by replacing glass-based models with a silver polymer sheet that has the same performance as the heavy glass mirrors, but at much lower cost and weight. It also is much easier to deploy and install. The glossy film uses several layers of polymers, with an inner layer of pure silver.

Telescope designer Roger Angel (Univ. of Arizona) has turned his attention to CPV, and is a partner in a company called Rehnu. Angel utilizes a spherical concentrating lens with large-telescope technologies, but much cheaper materials and mechanisms, to create efficient systems.[60]

Recent experience with CSP technology in 2014 - 2015 at Solana in Arizona, and Ivanpah in Nevada indicate large production shortfalls in electricity generation between 25 and 40 percent. Producers blame clouds and stormy weather, but critics seem to think there are technological issues. These problems are causing utilities to pay inflated prices for wholesale electricity, and threaten the long-term viability of the technology. As photovoltaic costs continue to plummet, many think CSP has a limited future in utility-scale electricity production.[61] On the other side, part of photovoltaic costs drop is the result of the fossil fuel cost reductions, which still powers most of PV production. Instead CSP would be unaffected when fossil prices return to higher quotes.

## Very large scale solar power plants

There are several proposals for gigawatt size, very large scale solar power plants. They include the Euro-Mediterranean Desertec proposal, Project Helios in Greece (10 gigawatt), and Ordos (2 gigawatt) in China. A 2003 study concluded that the world could generate 2,357,840 TWh each year from very large scale solar power plants using 1% of each of the world's deserts. Total consumption worldwide was 15,223 TWh/year[62] (in 2003). The gigawatt size projects are arrays of single plants. The largest single plant in operation is the 370 MW Ivanpah Solar. In 2012, the BLM made available 97,921,069 acres (39,627,251 hectares) of land in the southwestern United States for solar projects, enough for between 10,000 and 20,000 gigawatts (GW).[63]

## Effect on wildlife

It has been noted that insects can be attracted to the bright light caused by concentrated solar technology, and as a result birds that hunt them can be killed (burned) if the birds fly near the point where light is being focused onto. This can also affect raptors who hunt the birds.[64][65][66][67] Federal wildlife officials have begun calling these power towers "mega traps" for wildlife.[68][69][70]

However, the story about the Ivanpah Solar Power Facility was exaggerated, numbering the deaths in many tens of thousands, spreading alarm about concentrated solar power (CSP) plants, which was not grounded in facts, but on one opponent's speculation. According to rigorous reporting, in over six months, actually only 133 singed birds were counted.[71] By focusing no more than 4 mirrors on any one place in the air during standby, at Crescent Dunes Solar Energy Project, in 3 months, the death rate dropped to zero fatalities.[72]

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