The two-year rectenna construction schedule called for in the Reference System has a number of potentially significant implications relating to socioeconomic impacts on the siting region. The peak construction phase would seriously impact air quality, water supplies, and biological resources. The annual level of in-migration of construction workers, not including dependents and secondary employees associated with rectenna development, averages 2,500; with a peak of 3,200. There are also possible logistical problems, particularly with regard to the delivery to the site of enormous quantities of construction materials during the peak construction period. The delivery of 10 million tons of aggregate, 1.4 million tons of cement, and 370,000 tons of steel would require 2,400 heavy truck trips per day or six 100-car unit trains per day. An extended construction period would reduce the volume of deliveries at any one time and contribute to a diminution of all construction impacts, except the length of time they are present. 1 9 3. Energy Requirements Several energy analyses of the SPS have been conducted. In general, energy analysis attempts to determine the energy efficiency of a power plant. Other things being equal, it is better to build plants that require less energy for construction and maintenance. Two common measures of energy efficiency are energy ratio and payback period. The former is the net energy derived from a plant over its lifetime divided by the energy required to construct and maintain the plant. The payback period is the length of time the plant would be required to operate to generate the energy used in its construction and maintenance. It is customary to exclude the operating fuel when making these calculations and to restrict the energy requirements to nonrenewable sources. Under these conditions the SPS energy ratio is favorable, although usually less than coal and nuclear plants, depending on the specific assumptions used. Including nonrenewable fuel in the calculation makes SPS much better than coal or nuclear, since SPS is based on renewable energy. Energy payback periods for SPS have been calculated in the range of 1 to 6 years. Equivalent energy ratios would be 5 to 30. Coal and nuclear plants typically have energy ratios in the 5 to 15 range, excluding fuel. Uncertainties are larger for SPS
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