Solar concentrator technology, commonly referred to as concentrated solar power, stands in contrast to static photovoltaic panel electricity generating technologies, because it operates using moving parts, like a turbine, which can then generate electricity.
According to the Solar Energy Industries Association (SEIA), power plants with concentrating solar power, most often referred to in the short form as CSP, use mirrors to concentrate the Sun’s energy and drive traditional steam turbines or engines, which then generate electricity.
The thermal energy produced in a CSP plant can be stored and used to produce electricity when it is needed, day or night. Today, over 1,400 MW of CSP plants operate in the United States, and another 390 MW will be placed in service in the next year.
According to SolarServer, the most optimistic CSP industry development scenarios forecast that 7% of the power supply in 2030 may be generated with CSP technology, growing further to a possible share of 25% by 2050. More moderate assumptions of SolarPaces, the European Solar Thermal Electricity Association (ESTELA) and Greenpeace International assess the combined solar power output to contribute between 3 – 3.6% in 2030 and 8 – 11.8% in 2050 to the worldwide power supply. This means a capacity of over 830 GW in 2050.
Concentrated solar power history
Concentrated solar power is definitely not a new idea. There is plenty of interesting history to read on this technology, starting with sites like Wikipedia. Here we discover legend has it that Archimedes in battle 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. Even so, historians still doubt the Archimedes story, even if it makes great fiction.
Moving away from the tools of war, Auguste Mouchout used a parabolic trough in 1866 to produce steam for the first solar steam engine. And after this feat, Professor Giovanni Francia designed and built the first concentrated-solar plant, which began operation in Sant’Ilario, near Genoa, Italy in 1968. This plant featured 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.
Four primary CSP technologies
Thanks to the varied forms of engineering ingenuity, there are four primary technologies used in concentrated solar power plants around the world:
- Parabolic Trough – Parabolic trough systems used for concentrated solar power feature curved mirrors to focus the sun’s energy onto a receiver tube that runs down the center of a trough. In the receiver tube, a high-temperature heat transfer fluid (such as a synthetic oil) absorbs the sun’s energy, reaching temperatures of 750°F or even higher, and passes through a heat exchanger to heat water and produce steam. The steam drives a conventional steam turbine power system to generate electricity. A typical solar collector field contains hundreds of parallel rows of troughs connected as a series of loops, which are placed on a north-south axis so the troughs can track the sun from east to west. Individual collector modules are typically 15-20 feet tall and 300-450 feet long
- Compact Linear Fresnel Reflector – CLFR uses the principles of curved-mirror trough systems, but with long parallel rows of lower-cost flat mirrors. These modular reflectors focus the sun’s energy onto elevated receivers, which consist of a system of tubes through which water flows. The concentrated sunlight boils the water, generating high-pressure steam for direct use in power generation and industrial steam applications. AREVA Solar operates its 5 MW Kimberlina plant in Bakersfield, Calif., the first CLFR facility in North America. “The Kimberlina Solar Thermal Energy Plant.” Ausra, Inc. Accessed online 29 September 2011.
- Power Tower – Power tower systems use a central tower as a receiving point, allowing for extremely high operating temperatures. Computer-controlled flat mirrors (heliostats) track the sun along two axes and focus solar energy on a receiver at the top of a high tower. The focused energy can heat a transfer fluid (over 1,000° F) to produce steam and run a central power generator. SolarReserve features a 540-foot structure in Tonopah, Nevada at its Crescent Dunes Solar Energy Power Plant. This 110 MW plant is the first utility scale facility in the world to use advanced molten salt power tower energy storage capabilities. The project will deliver enough firm, reliable electricity from solar energy to power 75,000 homes in Nevada during peak demand periods, day and night, whether or not the sun is shining. The project, complete with construction and currently in the commissioning phase, will be the only operating utility scale molten salt power tower on the planet.
- Dish Engine – Mirrors are distributed over a parabolic dish surface to concentrate sunlight on a receiver fixed at the focal point. In contrast to other CSP technologies which use steam to create electricity via a turbine, a dish-engine system uses a working fluid such as hydrogen. The fluid is heated up to 1,200° F in the receiver to drive an engine. Each dish rotates along two axes to track the sun. SEIA reports a dish will generate 5-30 kilowatts of electricity depending on the system. Stirling and Brayton cycle engines are currently used for power conversion.
“As the penetration of variable renewable energy resources increases worldwide, more attention is being paid to the effects of renewable energy on power system reliability and operations,” said Tex Wilkins, executive director of the CSP Alliance in 2014. “As we explore in this report, CSP with thermal energy storage is a potential solution that meets clean energy and climate change policy goals, reduces the variability of the aggregate renewable energy portfolios and provides a wide range of operational and reliability benefits.”
Gemasolar is the first commercial-scale plant in the world to apply central tower receiver and molten salt heat storage technology. The relevance of this plant lies in its technological uniqueness, since it opens up the way for new thermosolar electrical generation technology. The prolongation of the plant’s operating time in the absence of solar radiation and the improvement in efficiency of the use of the heat from the sun makes Gemasolar’s output much higher than that which is delivered by other technologies in a facility with the same power.
BrightSource’s solar thermal system is operating at the Ivanpah Solar Electric Generating System (ISEGS) in California’s Mojave Desert. Ivanpah, which began commercial operation in 2013, is delivering power to PG&E and Southern California Edison. The project is currently the largest solar thermal power plant in the world. Ivanpah was constructed by Bechtel and is operated by NRG Energy, one of the project’s equity investors.