2. Per Unit Electricity Generation Costs The final step in the determination of the per unit cost of electricity generation from the total annual cost is shown in equation (1) of Exhibit 22. As noted in equation (2), annual cost itself is a complex calculation involving recurring costs, the recovery of capital costs, and the recovery of development (DDT&E) costs. Selected examples of the per unit cost calculations from several references are summarized in Exhibit 23. For purposes of this summary, all capital and recurring costs are expressed in dollars per rated kilowatt. Heading references indicate the baseline size, load factor, discount rate and total capital cost per kilowatt. Capital cost estimates per kilowatt show a wide variation, even within the same energy concept. Capital costs vary from $1,010 to $1,822 for photovoltaic systems and from $930 to $3,680 for solar-thermal (Brayton cycle) systems. All costs are in 1974, 1975 or 1976 dollars and specifically exclude DDT&E. As can be seen from the table, not even the components of annual operating costs are consistently defined. In the interest of providing some summary comparison, a standardized calculation, varying only with respect to stated interest rate, was made of the annual capital charge. Similarly, in some instances taxes, insurance, etc., were estimated at 5 percent of the capital cost when this approach was suggested in other tables in the same reference though not given explicitly in the SPS cost presentation. In general, this summary shows: first, the wide variation in capital cost; second, some important inconsistencies with respect to discount rate; and third, several instances of inflationary or otherwise unaccounted for variance. Finally, the grouping of solar photovoltaic costs in a range generally much lower than other SPS concepts suggests that, to the extent that the various analyses are at all comparable, the other processes seem at this time to be less attractive. One possible exception is the solarthermal (Brayton cycle) concept as estimated by JPL (Ref. A9). Unfortunately the briefing chart format of this reference provides no additional detail on either cost components or the precise methodology used in deriving unit costs.
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