Off-design performance of CSP plant based on supercritical CO2 cycles

In the near future, a significant increase of the fraction of electricity produced by variable renewable energy sources (wind and PV) is expected. In this scenario, concentrating solar power (CSP) plants, thanks to the implementation of cost-competitive thermal energy storage, can provide zero-emission back-up power improving system stability. Advanced sCO2 cycles are considered a promising option for next generation CSP plants, due to their higher efficiency, compactness of turbomachinery, simpler plant arrangement, no water consumption, high performance at part-load and fast transients. In the present work, a solar tower plant adopting sodium as heat transfer fluid (HTF) and a recompressed sCO2 cycle with a maximum temperature of 700°C as power conversion system is studied. The net cycle efficiency (46%) is maximized and a preliminary design of the heat exchangers is performed. The off-design operation of the cycle is then investigated evaluating the system performance using different operating strategies for two cases: (i) load variation and (ii) ambient temperature variation. The obtained results are compared in terms of cycle efficiency and in terms of compressor operating points, providing useful information on the compressors design.