MODELING OF PARABOLIC TROUGH DIRECT STEAM-GENERATION SOLAR COLLECTORS

Solar electric generation systems (SEGS) currently in operation are ba sed on parabolic trough solar collectors using synthetic oil heat tran sfer fluid in the collector loop to transfer thermal energy to a Ranki ne cycle turbine via a heal exchanger. To improve performance and redu ce costs direct steam generation in the collector has been proposed. I n this paper the efficiency of parabolic trough collectors is determin ed for operation with synthetic oil (current SEGS plants) and water (f uture proposal) as the working fluids. The thermal performance of a tr ough collector using Syltherm 800 oil as the working fluid has been me asured at Sandia National Laboratory and is used in this study to deve lop a model of the thermal losses from the collector. The model is bas ed on absorber wall temperature rather than fluid bulk temperature so it can be used to predict the performance of the collector with any wo rking fluid. The effects of absorber emissivity and internal working f luid convection effects are evaluated. An efficiency equation for trou gh collectors is developed and used in a simulation model to evaluate the performance of direct steam generation collectors for different ra diation conditions and different absorber tube sizes. Phase change in the direct steam generation collector is accounted for by separate ana lysis of the liquid, boiling and dry steam zones. (C) 1998 Elsevier Sc ience Ltd. All rights reserved.