Analytical modeling of direct steam generation solar power plants

Abstract

Analytical models for the physical processes governing direct steam generation line-focus solar thermal power plants are derived. Predictions compare favorably with the limited database available from published studies against which the accuracy of detailed model computations can meaningfully be assessed. That limited database should not be confused with extensive citations of system power delivery in the absence of comprehensive information. A physically transparent understanding is provided for heat transfer within the collectors, heat loss to ambient, fluid flow and steam cycle efficiency. With existing evacuated-tube parabolic-trough concentrators and steam turbines, net system conversion efficiencies can exceed 20% even for today’s small-scale (⩽100MW) power plants. A key limiting factor is that relatively low-power turbines inherently have poorer isentropic efficiencies than their high-power counterparts. Although a few strategies for improving system efficiency have previously been proposed, the analytical models presented here provide the ability to rapidly (a) quantify the performance advantages of these strategies and (b) project how assorted modifications should affect system behavior, in both cases, without the need for expansive simulations. Examples of these design options include (1) multiple fluid extractions in a regenerative turbine cycle, (2) higher isentropic efficiencies for larger turbines, and (3) raising cycle temperature.