Simulation and comparison between fixed and sliding-pressure strategies in parabolic-trough solar power plants with direct steam generation

Direct steam generation in parabolic-trough solar collectors is a promising technology that can improve the efficiency of solar thermal power plants. In this technology, water is heated and evaporated through the solar field to feed a steam Rankine cycle or an industrial thermal process. Regarding its application for electricity production, two main methods are commonly considered to regulate the steam pressure at the turbine inlet: fixed and sliding-pressure. In addition, the sliding-pressure method allows two different versions: constant and variable pressure in the condenser. This study aims to simulate the behaviour of a solar thermal power plant with direct steam generation applying the proposed strategies, by comparing their annual performance in terms of electricity production. To this end, a quasi-dynamic model able to address transient conditions with low computational resources has been applied. This model has been developed in the TRNSYS software environment and reproduces the behaviour of both the solar field and the power block of a 38.5 MWe solar thermal power plant. The results of this analysis demonstrate that the use of sliding-pressure strategies for steam pressure regulation in solar plants with direct steam generation is more advantageous in terms of net electricity production than the fixed-pressure method.