SUMMARY Parabolic dish collectors can be coupled to heat engines in a number of ways. Both distributed generation using a Brayton engine at each dish and central generation with a single large Rankine plant is possible. The central generation plants using steam or chemical energy transport have about a 20% cost advantage over the distributed generation concept with electric energy transport. Table 1 shows the capital cost breakdown for major subsystems for each of these three approaches and represent direct overnight construction costs. The total costs range from 1140 to 1435$/kWe. This difference may vanish when construction costs are considered such as interest during construction, escalation, spares, contingencies, and startup. The reason is the partial generation of power by the dish-Brayton combination during construction. Later economic analysis will evaluate this factor. The central generation plants using NaK and helium for energy transport proved to be too expensive, costing over 400$/kWe more than the steam or chemical approaches. The cost of pressurized water as the transport fluid was only 100$/kWe more than the cost of steam. However, there were additional penalties of a longer morning startup time (0.4 hour compared to 0.15 hour for steam and nil for chemical), but easier control with variable solar input. Table 1 also indicates the energy cost based on direct costs (no 0 & M), land area, and several other parameters. All three plants have a nearly neutral effect (using a first order of magnitude calculation) on the area heat balance compared to having no plant at all. The central generation plants use wet cooling towers and require 1100 acre ft/yr of cooling water. This may be a problem in the arid Southwest region. Using a dry cooling tower in the central generation plants, the direct capital costs increase by 150$/kWe, and the overall efficiency is reduced to ~0.9 of the efficiency obtained with a wet cooling tower.
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