Solar Thermal Electricity

Solar thermal electricity (STE) generates electricity from sunlight using standard steam generators (turbines).

Large-scale STE production with solar trough collectors can meet all national and global electricity demand. Other types of STE collector systems are also possible for ancillary production, such as to power desalination plants (see the DLR report in the References section below).

American engineer Frank Shuman proposed and built a solar trough collector plant in Egypt in 1913 (Figure 1). Originally planned to generate electricity with a generator (dynamo), a water pump was used instead, for agricultural irrigation. The plant generated 35 kilowatts (kW) of mechanical energy, with 1233 square meters (m²) of collector aperture area (Grasse et al., p. 215).

In the Shuman design (Figure 1), the parabolic reflectors are on rollers and rotate around the receiver fluid pipe axis. Now trough collectors move the receiver pipe along with the reflectors, on tracking stands with flexible pipes at the ends of the trough collectors (Figure 2).

Figure 2. Flexible pipe at end of collector (SEGS, Kramer Junction, California).

The SEGS solar trough plants in Kramer Junction, California have been operating for decades, and will last at least that much longer without requiring replacement costs as other electricity generating technologies require. The operating and maintenance (O&M) costs of Kramer Junction are only 2 cents per kilowatt-hour (kWh), which includes cleaning the collectors and periodic refurbishing of the steam turbines. Cost reduction work on one of the plants has lowered O&M costs to 1.22 cents per kWh, and future plants will have O&M costs below 1 cent per kWh (< US $ 0.01 / kWh).

Land with at least 6.5 kWh/m² per day direct normal irradiance (DNI) is suitable for generating solar thermal electricity. Figure 3 shows these areas for the United States in red and dark red:

Figure 4 shows limiting these areas to land with level ground, without environmental concerns, not containing urban areas, roads, lakes, other uses, etc., and with at least 1 km² of continuous land:

Sandia Labs estimates using solar trough plants on that land within the U.S. (marked orange and red in Figure 4, not yellow, and not the orange and red areas in Mexico) would produce 700 percent of U.S. electricity demand (i.e., one-seventh of that land would supply the nation's electricity).

Figure 5. Installing trough collectors. [ NREL ]

Solar trough technology does not require special materials. Standard metals and mirrors are used (e.g., steel and glass). No special elements need to be mined. Recycled materials can be used.

Adjacent solar trough plants each power a steam turbine that can generate up to 500 Megawatts (MW) of electricity per turbine, and future turbines may generate 1000 MW (1 GW) of electricity per turbine. Energy storage for peak demand extending into night (time-spread base load) will be with molten salt tank storage (to efficiently generate electricity at night).

Solar thermal electricity generation is especially productive in hotter regions that are not suitable for agriculture. The efficiency of these power plants increases with higher temperatures. Such land is ample and far exceeds the land area that is required to meet U.S. and global electricity needs. Research studies that do not use the hottest and driest land for STE are inaccurate.

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References:

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