Simulation of the part-load behavior of a 30 MWe SEGS plant

Abstract

The part-load behavior of a typical 30-MWe SEGS (solar electric generating systems) plant was studied using a detailed thermodynamic model. As part of this analysis, a new solar field model was derived, based on measurement results of an LS-2 Collector and accounting for various conditions of receiver tubes, lost mirrors and measured reflectivity. A comparison was made of the model results to real plant conditions for a winter and summer day in order to test the accuracy of the model. The effects of bare tubes, different wind speeds, mirror reflectivity and other factors were studied showing, e.g., that heat losses due to wind are predicted to be very low. The comparison also shows that the model still lacks the capability to fully account for actual solar field conditions. The model was also compared to the SOLERGY model, showing differences between the assumptions used in both models. Finally different operating conditions of the plant were studied for a summer, fall, and winter day to provide a better understanding of how changing solar field outlet temperatures affect gross and net output of the plant. This clearly indicates that the lowest possible superheating temperature maximizes the gross electric output. On a net basis this conclusion is modified due to the high parasitics of the HTF (heat transfer fluid) pumps. It was found that the optimum operating strategy depends on the insolation conditions, e.g., different superheating temperatures should be chosen in summer, fall and winter. If the pressure drop in the solar field is reduced due to replacement of flex hoses with ball joints, increasing the HTF flow is more reasonable, so that at low isolation conditions the lowest possible superheating temperature also leads to the maximum net output.