Otto J. M. Smith

ELECTRIC GENERATORS FOR SMALL SOLAR-THERMAL SYSTEMS

ABSTRACT Induction machines are suitable electric generators for small solar-thermal systems using a Rankine-cycle turbine. The turbine shaft is coupled to a 2-pole induction machine which feeds into an alternating current public utility. Remote solar installations are often serviced by only single-phase public utilities. Three-phase machines, however, are more efficient than single-phase machines, cost less, and have less vibration. A three-phase induction generator coupled to a turbine can be operated at balanced voltages and currents, and feed single-phase power into a single-phase line using this new winding connection with capacitors.

A HELIOELECTRIC FARM

ABSTRACT A multimodule solar thermal electric plant has been designed to use conventional materials and engineering techniques. Each module occupies only 0.8 hectare and contains 500 mirrors of 2.4 square meters each. 600 modules, each with a heat receptor on a short tower, collect solar energy for a 100 MW generator operating 12 hours a day. Sophisticated computer programs are used for both design and plant operation. The design program minimizes bus bar cost by finding the most cost-effective mirror dimensions, spacing, module dimensions, tower height, and receptor dimensions. The operation program completely surveys the solar field, calibrates all shaft encoders and control devices, and aims the reflected solar light toward the tower all by computer software. No engineering adjustments or manual check-out is needed in the solar farm. A land area of 550 hectares is sufficient to produce 500,000 megawatt-hours of electric energy each year. This can be a 100 MW, 50-percent duty factor plant, or 70-MW, 70-percent duty factor, or 50 MW base load plant, with no significant change in megawatt-hour cost. 480 hectares is used for heliostat fields, and 70 hectares is used for radiative heat-rejection panels. The latter eliminate the need for a dry cooling tower, and partially compensate for heat pollution from fossil-fuel plants. The 300,000 small mirrors and 600 short towers permit mass production techniques to significantly reduce the manufacturing cost. The mirror costs are a predominant part of the total system cost, and minimizing the mirror cost produces an economically competitive power plant. Estimated manufacturing and installation cost including interest during construction is 175 million dollars for each 100 MW power plant. Estimated operations, maintenance, and repair costs are 4 million dollars per year. Half of the construction cost is direct labor wages, which would make a desirable impact on employment and economy. A building program of 1000 solar megawatts each year would support 40,000 maintenance laborers with wages of 400 million dollars per year (in 1978 dollars). These workers would be employed on a solar farm of less than 30 km square. The Smith Multimodule Solar Thermal Electric System uses small hexagonal interlocking modules that minimize piping and land costs. Smiths system used a molten salt for a heat transfer fluid (HTF) which is pumped from the solar receptors on 27-meter tall towers into the power house