Solar Thermal Electric Power Plants can be Cost Effective

Solar Thermal Electricity

In the 1970s Dr. Otto J.M. Smith of U.C. Berkeley's Electrical Engineering department proposed a solar thermal electric power plant built entirely from off-the-shelf components. After reading that commercial engineering firms were proposing a single tower power plant design to be funded by the federal government, Dr. Smith decided to investigate the problems of producing electricity from the Sun's heat. One of the advantages of a solar thermal plant is that the heat energy can be stored in liquid salt solutions that it can be used to generate electricity for three continuous days of cloudy weather.

Solar Heat Drives Turbines

A solar thermal power plant uses fields of mirrors to reflect heat onto a collector which then heats a transfer fluid. The heated fluid travels to a power house where it expends its energy in turning a turbine, which turns a generator to produce electricity. In this way process is similar to a conventional coal, natural gas, or nuclear power plant; heated fluid turns a turbine which then turns a generator. Since the major technological steps have been developed, the challenge is to engineer the costs down. See also the Sun Lab.

The Mirrors are Most Expensive

Dr. Smith's calculations showed him that the mirrors comprised the majority of the expense of the power plant. So reducing the cost of the mirrors would have the most impact on reducing the cost of the plant. Rather than constructing one, tall, central collecting tower, Smith proposed several smaller 60 ft. towers which would be served by hexagonal shaped fields of mirrors placed the the north. The collecting towers would not be placed in a circular mirror field. Since the mirrors do not have to be as accurate in reflecting light long distances to a single tower, they can be flat plate collectors made out of cheaper mylar film, as opposed to expensive flat or parabolic glass reflectors. Tracking the Sun as it moves across the sky can be complicated for hundreds of large mirrors which must be precisely controlled. Smith's mirrors were smaller, easier to control and repair. And since Dr. Smith calculated that mirror fields and controls represented over 3/4 of the cost of the plant, any reduction in the cost of mirrors makes a major impact in reducing overall costs. In addition, by using multiple towers, the power plant is modular so that individual mirror fields can be shut down for maintenance and repairs without substantially reducing the output of the entire solar electric plant. The towers themselves are not as expensive since they are only 60 ft., as opposed to the proposed 300 ft. to over 1000 ft. tower originally proposed, and are easier to construct, erect, and support.

Available Technology

By using off-the-shelf parts and materials, Dr. Smith's proposed design costs over 80 percent less then the designs under consideration by the Federal government at the time. Smith argued that since the basic technology used in collecting sun light to boil a fluid and turn a turbine and generator were essentially understood. The major challenge was finding ways to reduce the costs involved. Therefore, aerospace companies were not the most likely contractors to build a cost-effective solar power plant. Aerospace engineers traditionally have been best at developing exotic technologies, such as fuel cells and compact computers, where reducing the size and weight of components have been the highest priority, not reducing mass production costs. Instead, contract with corporations such as Toyota or General Motors where engineers are accustomed to taking a known technology, such as the internal combustion engine, and reducing the manufacturing costs while increasing the over all performance. These are the skills required to construct cost-effective, reliable solar thermal power plants. And these skills are different from those needed to develop cutting-edge, exotic technologies.

Design Updates

Since that original design Dr. Otto Smith has developed a far superior design, using two kinds of solar mirror fields and two different temperatures of molten salt heat storage, for an all-solar high-efficiency low-cost base-load plant not using any fossil fuels. Solar thermal plants can store heat in the form of molten salt to provide electricity 18 to 24 hours per day. A 100-MW power plant could be built for $700 million and generate electricity for eight cents per kilowatt hour. Presently California is paying from 10 cents to over a dollar per kilowatt hour for peak electrical power.

Free Solar Fuel

Since the energy source, solar heat, is free and renewable, the solar thermal power plant is immune to fuel price fluctuations and availability. This must be factored into the over all operating cost of the plant since often power plants which use renewable fuel cost more in the construction phase when compared to the installed capacity of fossil fuel plants. When the cost of the fuel is included over the life cycle of the plant, solar thermal power can be competitive with fossil fuel and nuclear power. The natural availability of solar heat nicely matches the summer electricity demand curve as air conditioners kick in during afternoon hours when solar plants would be reaching their peak output. Solar thermal power, then, could play an important role in supplying the electrical power grid in the western United States, along with existing hydroelectric and natural gas plants.

Where Do We Build the Solar Plants?

The land required to build such plants is cheap. Dr. Smith proposed using Federal B.L.M. land in the southwest, or parts of U.S. military testing or firing ranges. Theoretically, one large plant built in a square 100 miles on a side could provide the base load electrical needs of the entire U.S.. And unlike nuclear power, solar electric plants can be dismantled and decommissioned relatively easily when they reach the end of their life cycle. The plant can be removed without leaving any radioactive contamination to the land. The cost of decommissioning nuclear power plants is in the billions of dollars.
According to Solar Developments, "Utilizing only 1% of the earth's deserts to produce clean solar electric energy would provide more electricity than is currently being produced on the entire planet by fossil fuels."

Solar Power Paves the Way to the Eventual Hydrogen Economy

One alternative to producing electricity for the Western States power grid would be to use solar electricity to produce hydrogen fuel from water. Electricity can be used to separate the hydrogen from oxygen in water. When hydrogen is burned as a fuel it then produces water again. Hydrogen fuel could also be used for fuel cells in buildings and cars to produce electricity and heat. As we transition from a fossil fuel economy to a renewable "hydrogen economy", hydrogen offers many advantages as a fuel since it is plentiful, renewable, and produces almost no air pollution and few greenhouse gases. Ultimately renewable sources of energy such as solar, wind, and hydroelectric will be used to produce hydrogen fuel for fuel cells.

Efficient Electric Motor

Dr. Otto J.M. Smith is a Professor Emeritus at U.C. Berkeley and has also invented both a large high-efficiency single-phase motor and a low-frequency sine-function generator originally manufactured by Hewlett-Packard and now manufactured and used world-wide. This motor is 10 percent more efficient then most existing electric motors. He is also a fellow of both the Institute of Electrical and Electronic Engineers and the American Association for the Advancement of Science, and is now the CEO of Smith and Sun®.

Energy Action Project