The challenge of solar powered combined cycles – Providing dispatchability and increasing efficiency by integrating the open volumetric air receiver technology

This work analyzes the performance potential of solar-only powered combined cycles, comparing the impact of two different solar receiver technologies (opaque-heat-exchanger-type vs. volumetric). Due to material and receiver performance constraints, as well as the absence of internal combustion, the gas turbine inlet temperature (TIT) is limited to considerably lower values than observed in current fossil-fired state-of-the-art combined cycle plants. Therefore, the analysis includes the evaluation of a reheated topping Brayton cycle, aiming for a higher mean temperature of the heat input, thereby allowing fair conversion efficiencies despite moderate TITs. An extensive parametric optimization analysis compares different solar combined cycle configurations and benchmarks them against conventional CSP single-cycle plants. High thermal losses in the receiver tend to offset the gain allowed by the power cycle. The innovative coupling of an open volumetric air receiver with a regenerative heat exchange system that works in alternating operating modes (non-pressurized heating period, pressurized cooling period) could be a promising solution to efficiently drive a solar powered combined cycle. Furthermore, the optimum solar combined cycle performance for typical mean concentration ratios (C ≈ 500) is fully compatible with high temperature TES, providing the promising possibility of fully dispatchable operation at highest thermal-to-electric conversion efficiency.