The third type uses a parabolic dish to focus the sunlight onto a receiver at the focal point of the parabolic dish. The receiver contains a fluid that can drive a generator. The original design used a Stirling engine driven by an expanding fluid, such as air.
Some of the projects that were to use concentrating solar (CSP) are being converted to PV arrays where PV panels are arrayed over a wide area. Costs are driving these changes.
For example, Stirling Energy Systems filed for bankruptcy on September 23
Many of the CSP projects are receiving loan guarantees or grants from the Department of Energy.
Concentrating solar requires high levels of insolation (solar intensity) and can only be used in the desert southwest of the United States. The measurement for insolation is watts-per-square meter. Spain, with moderatly high levels of insolation was a major developer of CSP. The dark orange areas of the map are the areas suitable for CSP in the United States.
(Insolation should not be confused with insulation.)
USA Irradiation Map
These systems have capacity factors of between 16% and 22%, which means that they produce small amounts of electricity when compared with natural gas, coal or nuclear, which have capacity factors of between 75% and 92%.
Efforts are being made to improve the ability of a CSP system to generate electricity after the sun sets by storing heat in a salt reservoir. The heat from the salt reservoir can last for around four hours, which extends the CSP plant’s ability to generate electricity.
The cost of generating electricity from CSP systems is around 30 cents per kWh without subsidies, though this figure is disputed by CSP advocates. Obviously, if CSP could compete with natural gas and coal, CSP plants would be built without subsidies. These systems also require expensive, dedicated transmission lines to bring the electricity to where it can be used.
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