Concentrating Solar Power

Concentrated solar power (CSP) systems use lenses or mirrors to focus a large area of sunlight onto a small area. Electrical power is produced when the concentrated light is directed onto photovoltaic surfaces or used to heat a transfer fluid for a conventional power plant.

Concentrated solar power systems are divided into

  • concentrated solar thermal (CST)
  • concentrated photovoltaics (CPV)
  • concentrating photovoltaics and thermal (CPT)

Concentrated solar thermal

Concentrated solar thermal (CST) is used to produce renewable heat or electricity (generally, in the latter case, through steam). Concentrated solar thermal (CST) systems use lenses or mirrors and 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).

A wide range of concentrating technologies exist, including the parabolic trough, Dish Stirling, Concentrating Linear Fresnel Reflector, Solar chimney and solar power tower. Each concentration method is capable of producing high temperatures and correspondingly high thermodynamic efficiencies, but they vary in the way that they track the Sun and focus light. Due to new innovations in the technology, concentrating solar thermal is becoming more and more cost-effective.

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 is filled with a working fluid. The reflector follows the Sun during the daylight hours by tracking along a single axis. A working fluid is heated to 150–350 °C (423–623 K (302–662 °F)) as it flows through the receiver and is then used as a heat source for a power generation system. Trough systems are the most developed CSP technology. The Solar Energy Generating Systems (SEGS) plants in California, Acciona's Nevada Solar One near Boulder City, Nevada, and Plataforma Solar de Almería's SSPS-DCS plant in Spain are representative of this technology.

Concentrating 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 reflector can come in large plants or more compact plants.

A Dish Stirling or dish engine system consists of a stand-alone parabolic reflector that concentrates light onto a receiver positioned at the reflector's focal point. The reflector tracks the Sun along two axes. The working fluid in the receiver is heated to 250–700 °C (523–973 K (482–1,292 °F)) and then used by a Stirling engine to generate power. Parabolic dish systems provide the highest solar-to-electric efficiency among CSP technologies, and their modular nature provides scalability. The Stirling Energy Systems (SES) and Science Applications International Corporation (SAIC) dishes at UNLV, and the Big Dish in Canberra, Australia are representative of this technology.

A Solar chimney consists of a transparent large room (usually completely in glass) which is sloped gently up to a central hollow tower or chimney. The sun heats the air in this greenhouse-type structure which then rises up the chimney, hereby driving an air turbine as it rises. This air turbine hereby creates electricity. Solar chimneys are very simple in design and could therefore be a viable option for projects in the developing world.

A solar power tower consists of an array of dual-axis tracking reflectors (heliostats) that concentrate light on a central receiver atop a tower; the receiver contains a fluid deposit, which can consist of sea water. The working fluid in the receiver is heated to 500–1000 °C (773–1,273 K (932–1,832 °F)) and then used as a heat source for a power generation or energy storage system. Power tower development is less advanced than trough systems, but they offer higher efficiency and better energy storage capability. The Solar Two in Daggett, California and the Planta Solar 10 (PS10) in Sanlucar la Mayor, Spain are representative of this technology. eSolar's 5 MW Sierra SunTower located in Lancaster, California and is the only CSP tower facility operating in North America.

Concentrated Solar Thermal Power (CSP) is the main technology proposed for a cooperation to produce electricity and desalinated water in the arid regions of North Africa and Southern Europe by the Trans-Mediterranean Renewable Energy Cooperation DESERTEC.

Concentrated photovoltaics

Concentrated photovoltaics (CPV) systems employ sunlight concentrated onto photovoltaic surfaces for the purpose of electrical power production. 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.

Serious research and development work on concentrator PV systems has been conducted since the 1970s. For example, a linear-trough concentrator system was tested and installed at Sandia National Laboratories, and the first modern point focus photovoltaic concentrating system was developed in the Sandia, both late in that decade. The latter system used a point focus acrylic Fresnel lens focusing on water-cooled silicon cells and two axis tracking. A similar concept was used in other prototypes. Ramón Areces' system, developed in the late 1970’s, used hybrid silicone-glass Fresnel lenses, while cooling of silicon cells was achieved with a passive heat sink.

Luminescent solar concentrators (when combined with a PV-solar cell) can also be regarded as a Concentrating photovoltaics (CPV) system. Luminescent solar concentrators are useful as they can improve performance of PV-solar panels drastically.


Semiconductor properties allow solar cells to operate more efficiently in concentrated light, as long as the cell junction temperature is kept cool by suitable heat sinks. CPV operates most effectively in sunny weather since clouds and overcast conditions create diffuse light, which essentially cannot be concentrated.

Expected future efficiencies are nearly 50%.

Grid Parity

Compared to conventional flat panel solar cells, CPV is advantageous because the solar collector is less expensive than an equivalent area of solar cells. CPV hardware (solar collector and tracker) is targeted to be priced well under 3 USD/Watt, whereas silicon flat panels that are commonly sold are 3 to 5 USD/Watt (not including any associated power systems or installation charges).

CPV could reach grid parity in 2011.

Low concentration CPV

Low concentration CPV are systems with a solar concentration of 2-100 suns. For economic reasons, conventional or modified silicon solar cells are typically used, and, at these concentrations, the heat flux is low enough that the cells do not need to be actively cooled. The laws of optics dictate that a solar collector with a low concentration ratio can have a high acceptance angle and thus in some instances does not require active solar tracking.

Medium concentration CPV

From concentrations of 100 to 300 suns, the CPV systems require two-axes solar tracking and cooling (whether passive or active), which makes them more complex.

High concentration photovoltaics (HCPV)

High concentration photovoltaics (HCPV) systems employ concentrating optics consisting of dish reflectors or fresnel lenses that concentrate sunlight to intensities of 300 suns or more. The solar cells require high-capacity heat sinks to prevent thermal destruction and to manage temperature related performance losses. Multijunction solar cells are currently favored over silicon as they are more efficient. The efficiency of both cell types rises with increased concentration; multijunction efficiency also rises faster. Multijunction solar cells, originally designed for non-concentrating space-based satellites, have been re-designed due to the high-current density encountered with CPV (typically 8 A/cm2 at 500 suns). Though the cost of multijunction solar cells is roughly 100 times that of comparable silicon cells, the cell cost remains a small fraction of the cost of the overall concentrating PV system, so the system economics might still favor the multijunction cells.

Much of the original research into multijunction photovoltaics was sponsored by governments and the astronautics industry. More recently, the technical research and product development of CPV systems has grown due to investment in terrestrial electric generating systems. Recent technological advances in triple-junction solar cells by Fraunhofer Institute ISE have yielded 41.1% conversion efficiency.

In May 2008, IBM demonstrated a prototype CPV using computer chip cooling techniques to achieve an energy density of 2300 suns.

Recently, Concentrix (Germany) and Amonix (USA) have announced operating AC efficiencies of 23% and 25%, respectively. These numbers point to significantly higher annual energy generation per receiver area unit with HCPV than with competing technologies.

In November 2009, NREL released a technical report presenting the opportunities and challenges of CPV technology, from a state of the art review.

In March 2010, OPEL Solar 330 kilowatts (kW) utility-grade solar photovoltaic power plant in Spain is one of the first HCPV installations to be recognized with an feed-in tariff (FIT) and guaranteed investment rate of return. The installation features dual-axis tracker-mounted Opel Mk-I HCPV panels, which can focus more than 500 suns onto high-efficiency multijunction GaAs solar cells. and has conversion efficiency up to twice that of silicon solar panels and more than three times that of thin-film solar panels.

In China Suntrix design and produce HCPV module.They have 500x and 1000x products.

Concentrated Photovoltaics and Thermal

Concentrating Photovoltaics and Thermal (CPVT) technology produces both electricity and thermal heat in the same module. Thermal heat that can be employed for hot tap water, heating and heat-powered air conditioning (solar cooling), desalination or solar process heat.

CPVT systems can be used in private homes and increase total energy output to 40-50%, as compared with normal PV panels with 10-20% efficiency, and they produce more thermal heat in wintertime compared with normal thermal collectors. Also, thermal systems do not overheat.

Australian, American, and Chinese researchers are exploring the potential for Combined Heat and Power Solar (CHAPS), while Europeans are now producing CHAPS systems.


As at September 9, 2009; 8 months ago (2009-09-09), the cost of building a CSP station was typically about $2.5 to $4 per watt, while the fuel (the sun's radiation) is free. Therefore a 250MW CSP station would have cost $600–1000 million to build. That works out to 12 to 18 cents per kilowatt-hour.

Future of Concentrated Solar Power

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. Also, with this expansion of concentrated solar power, thousands of new jobs would be created and millions of tonnes of carbon dioxide would be prevented from being released. The increase in investment would be from 2 billion euros worldwide to 92.5 billion euros in that time period. Spain is the leader in concentrated solar power technology, with more than 50 projects approved by the government in the works. Also, it exports its technology, further increasing the technology's stake in energy worldwide. Because of the nature of the technology needing a desert like area, experts predicted the biggest growth in places like Africa, Mexico, the southwest United States. 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:

Time Investment Capacity
2015 21 billion euros a year 420 megawatts
2050 174 billion euros a year 1500 gigawatts

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 .23 to .15 euros per kilowatt, down to .14 to .10 euros a kilowatt. Recently the EU has begun to look into developing a €400 billion ($774 billion) solar power plant based in the Sahara region using CSP technology known as Desertec. It is part of a wider plan 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.

Other organizations expect CSP to cost $0.06(US)/kWh by 2015 due to efficiency improvements and mass production of equipment. 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 September 9, 2009; 8 months ago (2009-09-09), Bill Weihl,'s green energy czar 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.

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 a much lower cost and much lower 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.

Development, Deployment and Economics of Solar Power

Beginning with the surge in coal use which accompanied the Industrial Revolution, energy consumption has steadily transitioned from wood and biomass to fossil fuels. The early development of solar technologies starting in the 1860s was driven by an expectation that coal would soon become scarce. 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.

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 US (SERI, now NREL), Japan (NEDO), and Germany (Fraunhofer Institute for Solar Energy Systems ISE).

Between 1970 and 1983 photovoltaic installations grew rapidly, but falling oil prices in the early 1980s moderated the growth of PV from 1984 to 1996. Photovoltaic production growth has averaged 40% per year since 2000 and installed capacity reached 10.6 GW at the end of 2007, and 14.73 GW in 2008. Since 2006 it has been economical for investors to install photovoltaics for free in return for a long term power purchase agreement. 50% of commercial systems were installed in this manner in 2007 and it is expected that 90% will by 2009. Nellis Air Force Base is receiving photoelectric power for about 2.2 ¢/kWh and grid power for 9 ¢/kWh.

Commercial concentrating solar thermal power (CSP) plants were first developed in the 1980s. CSP plants such as SEGS project in the United States have a levelized energy cost (LEC) of 12–14 ¢/kWh. The 11 MW PS10 power tower in Spain, completed in late 2005, is Europe's first commercial CSP system, and a total capacity of 300 MW is expected to be installed in the same area by 2013.

In August 2009, First Solar announced plans to build a 2 GW photovoltaic system in Ordos City, Inner Mongolia, China in four phases consisting of 30 MW in 2010, 970 MW in 2014, and another 1000 MW by 2019. As of June 9, 2009, there is a new solar thermal power station being built in the Banaskantha district in North Gujarat. Once completed, it will be the largest solar power plant in the world.

World's largest concentrating solar thermal power stations
Technology type Name Country Location
354 parabolic trough Solar Energy Generating Systems USA Mojave desert California
75 parabolic trough Martin Next Generation Solar Energy Center USA near Indiantown, Florida
64 parabolic trough Nevada Solar One USA Las Vegas, Nevada
50 parabolic trough Andasol 1 Spain Granada
20 solar power tower PS20 solar power tower Spain Seville
11 solar power tower PS10 solar power tower Spain Seville

Solar power plant installations in recent years have also begun to expand into residential areas, with governments offering incentive programs to make "green" energy a more economically viable option. In Ontario, Canada, the Green Energy Act passed in 2009 created a feed-in-tariff program that pays up to 80.2¢/kWh to solar PV energy producers, guaranteed for 20 years. The amount scales up based on the size of the project, with projects under 10KW receiving the highest rate. (People participating in a previous Ontario program called RESOP (Renewable Energy Standard Offer Program), introduced in 2006, and paying a maximum of 42¢/kWh, were allowed to transfer the balance of their contracts to the new FIT program. The program is designed to help promote the government's green agenda and lower the strain often placed on the energy grid at peak hours. In March, 2009 the proposed FIT was increased to 80¢/kWh for small, roof-top systems (≤10 kW).

World's largest photovoltaic (PV) power plants
Name of PV power plant Country DC
Olmedilla Photovoltaic Park Spain 60 85 0.16
Strasskirchen Solar Park Germany 54 57
Lieberose Photovoltaic Park Germany 53 53 0.11 2009
Puertollano Photovoltaic Park Spain 50

Moura photovoltaic power station [68] Portugal 46 93 0.16 Completed December 2008
Kothen Solar Park Germany 45

Finsterwalde Solar Park Germany 42

Waldpolenz Solar Park[69][70] Germany 40 40 0.11 550,000 First Solar thin-film CdTe modules. Completed December 2008
Planta Solar La Magascona & La Magasquila Spain 34.5

Arnedo Solar Plant Spain 34

Completed October 2008
Planta Solar Dulcinea Spain 31.8

Completed 2009
Merida/Don Alvaro Solar Park Spain 30

Completed September 2008
Planta Solar Ose de la Vega Spain 30

Planta Fotovoltaico Casas de Los Pinos Spain 28

Planta Solar Fuente Alamo Spain 26 44

DeSoto Next Generation Solar Energy Center[71][72] USA 25 40
SunPower. President Obama visited October 27, 2009. Completed October 2009
Financial incentives supporting installation of solar power generation are aimed at increasing demand for solar photovoltaics such that they can become competitive with conventional methods of energy production. Another innovative way to increase demand is to harness the green purchasing power of academic institutions (universities and colleges). This has been shown to be potentially influential in catalyzing a positive spiral-effect in renewables globally