4. A preliminary identification and analysis of utility interface issues and problems. The continued refinement of cost estimates and costing methodologies was of particular interest during this phase of the study. To satisfy these objectives, a significant part of the study effort was devoted to the development and use of cost and cost-risk analysis computer models. These models are used to combine economic and technical data to provide information for programmatic decision making. Thus, the results of the second study phase differ from those of the first study phase in two basic ways: 1. They are nondeterministic; that is, results are given in the form of probability distributions rather than single number estimates. 2. It is not assumed that all technology goals are met, rather the chance of achieving various levels of technology developments were assessed and the corresponding system cost impacts evaluated. The results of the cost-risk analysis were used to assess the economic viability of various SPS development program plans and to identify the critical technology areas. The economic viability, that is, the net present value, of the second SPS unit was assessed subject to the following assumptions: 1. The SPS unit availability factor is 0.95; that is, it is producing power 95 percent of the time. This includes power outages due to solar eclipses near the equinoxes. 2. The power output of the SPS unit decreases by 1 percent per year due to degradation of various components. 3. The lifetime of the SPS unit is 30 years. 4. The capital investment in the SPS unit is made in one lump-sum payment 2 years prior to the initial operation date of the SPS unit. 5. The real price of power at the rectenna busbar (1974 dollars) increases at the rate of 1 percent per year. 6. No charge is made for taxes and insurance. 7. Present value computations use a discount rate of 7. 5 percent.
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