System level analysis of a sodium boiler receiver and PCM storage CSP plant using solartherm

Abstract

A system-level evaluation of a concentrating solar power (CSP) configuration, with high-temperature sodium boiler receiver, direct-contact NaCl phase change material (PCM) storage and a Stirling engine array at 1 MWe scale was performed using the modelling framework of SolarTherm to provide an estimate of system costs and comparison to a reference 100 MWe two-tank molten salt system. Assuming an allowable receiver peak flux limit of 1.75 MWth/m2 and a Stirling engine efficiency of 34.6%, a levelised cost of energy (LCOE) of 137 USD/MWhe is obtained via genetic optimisation of parameters including solar multiple, receiver size, and storage component geometry. For an optimistic power cycle efficiency at 75% of the Carnot limit, the calculated LCOE is 109 USD/MWhe. Assuming safety risks can be mitigated without major additional cost, this novel concept holds promise when compared to the reference case that has an LCOE of 123 USD/MWhe, especially for small-scale opportunities either off-grid or at the fringe-of-grid. As this concept operates at very high temperature, the thermal efficiency of the receiver is lower than for a conventional CSP plant, and the storage system is more expensive on a unit-cost basis due to the use of high strength alloys in the tank. However, these drawbacks are offset by the use of a low-cost steel lattice tower design which is feasible at small scale, and by high efficiency power conversion at ~800°C.