Solar thermal power plants, also referred to as concentrating solar power (CSP) plants, utilize mirrors to focus the sun's energy onto a receiver where a fluid is heated and used to drive a generator. There are three main types of CSP systems as described in the Video 1:
- Linear concentrator systems collect the sun's energy using long rectangular, curved mirrors which focus sunlight on tubes that run the length of the mirrors. This heats a fluid flowing through the tubes which is used to boil water in a conventional steam-turbine generator to produce electricity. See Figure 1.
- Dish/engine systems use a mirrored dish similar to a very large satellite dish. The dish-shaped surface directs and concentrates sunlight onto a thermal receiver, which absorbs and collects the heat and transfers it to the engine generator. The most common type of heat engine used today in dish/engine systems is the Stirling engine. This system uses the fluid heated by the receiver to move pistons and create mechanical power. The mechanical power is then used to run a generator or alternator to produce electricity. See Figure 2.
- Power tower systems use a large field of flat, sun-tracking mirrors known as heliostats to focus and concentrate sunlight onto a receiver on the top of a centrally located tower. The receiver converts the solar energy to heat. The heat is used to boil water to create steam which is then used to power a conventional steam generator and generate electricity.
The Ivanpah Solar Electric Generating System, located in California in the Mojave Desert, is the largest CSP plant in the world. It consists of three fields of heliostates and three 459-foot tall towers and can generate 392 MW of electricity. See Videos 2 and 3.
A variation of the technology utilizes molten nitrate salt as the heating fluid because of its superior heat-transfer and energy-storage capabilities. The molton salt can be used to boil water and generate electricity immediately, or it can be stored for later use. The ability to store energy on a large scale allows the system to continue to generate electricity during cloudy weather or at night. It also allows the solar plant to be used as a dispatch resource for the electrical grid. Thus, when the grid operator must quickly ramp-up power to handle a problem, the solar plant can be used rather than the traditional gas or coal plant.
The 110 MW Crescent Dunes Solar Energy Project located near Tonopah, Nevada, is the largest CSP plant that incorporates such a storage system. It consists of a single 540-foot tall tower and approximately 174,000 heliostats. See Video 4.
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