Feasibility and Energetic Assessment of a Hybrid Solar Tower-Parabolic Trough Power Plant

Solar tower and parabolic trough technologies are a promising combination to overcome individual limitations of the concentrated solar power (CSP) systems. At high operating temperatures up to 1000°C, solar towers of21r high thermodynamic efficiency and cost-effective thermal storage, whereas parabolic troughs offer technical maturity and reliable performance with medium operating temperatures (≈400°C). This study discusses feasibility assessment and energetic evaluation of a hybrid solar tower-parabolic trough power plant, in which parabolic trough field provides extra thermal energy to the Rankine bottoming cycle of the solar tower plant. To obtain a detailed one-dimensional steady state thermal and hydraulic model of the parabolic trough collector, all major heat transfer mechanisms (radiation, convection and conduction) along the receiver tube was considered. Operationally obtained data at Andasol power plant and Luz LS-3 collector were used to validate the model. The thermal production from the trough system for a clear sky “perfect solar day” was then added to the optimized solar tower model of Spelling (2008) using pinch analysis and heat exchanger network synthesis. Various integration scenarios and trough field capacities (5MWth to 2000MWth) were explored. The results demonstrate that the hybrid configuration has a very significant effect on the performance of the plant. The overall energetic efficiency goes up from 18.5% with the tower only configuration to a maximum of 27.1% with an optimal trough capacity of ~1000 MWth. The exergetic efficiency is also enhanced by up to 38%. The technical feasibility of the concept is verified using composite curves, Sankey diagrams and three-dimensional efficiency maps to locate the heat integration points in the Rankine cycle. Placing the parabolic trough field behind the heliostat field, as proposed, has practical benefits such as minimizing piping losses and maximizing land utilization. The hybrid approach is one promising route towards large-scale, cost-effective, efficient and dispatchable solar power generation.