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).

Trough Collectors

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).

Figure 1. Shuman solar trough collectors in Meadi, Egypt, 1913, near the Nile River.

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).

“Parabolic trough collectors have been used in the Mojave Desert in California since 1984. The power plants of the Solar Energy Generating Systems (SEGS) have a combined generating capacity of 354 MW. Despite the harsh conditions, the reflector arrays continue to function perfectly to the present day.”
— 
Desertec

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 3. Direct normal irradiance (DNI) in the United States. [ NREL 105 K ]

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:


Figure 4. Southwestern United States and Northern Mexico. AC transmission lines are shown (DC lines are not shown). [ NREL 1 MB ]

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.

“The only technology presently available for [load follow over a large range of power output] is conventional coal power plants, which are the main tool for dispatchers to control the grid. ST (solar thermal) has here a potential edge, and such plants are the most attractive application of ST today, as they are already cost competitive.”
— 
Shinnar & Citro, Technology in Society, 29(2007):265
“The dry tropics and subtropics receive more global radiation annually than any other zone, including those at a similar latitude or closer to the equator… The total area of the ecozone is 31 million km² or 20.8 percent of the world landmass.”
— 
Jurgen Schultz, Ecozones of the World, 2/e:170,169
“Well-meaning scientists, engineers, economists and politicians have proposed various steps that could slightly reduce fossil-fuel use and emissions. These steps are not enough … Solar energy's potential is off the chart.”
— 
Scientific American, Jan. 2008
“The expansion of wind energy, or photo-voltaic use could induce additional resource and energy flows…instead of accordingly reducing energy from fossil fuels and nuclear power.”
— 
Niko Paech, in Innovations Toward Sustainability, p. 122

Contents of This Report

Page 1 : 
Page 2 : 
Page 3 : 
Page 4 : 
Page 5 : 
Introduction (this page)
Kramer Junction
Reflectors
Cleaning
Other Systems

Next Page:
Page 2

References:

 1.  W. Grasse, H. P. Hertlein and C.-J. Winter, “Thermal Power Plants Experience”, Ch. 7 in C.-J. Winter, R. L. Sizmann, L. L. Vant-Hull, eds., Solar Power Plants: Fundamentals, Technology, Systems, Economics, Springer 1991. [ WorldCat ]

 2.  Franz Trieb, et al., Concentrating Solar Power for Seawater Desalination, DLR (German Aerospace Center), November 2007. [ pdf 7.6 MB ]

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