Techno-Economic Evaluation of Future Thermionic Generators for Small-Scale Concentrated Solar Power Systems

Abstract

Small-size concentrated solar power (CSP) plants are presently not diffused due to a too-high levelized cost of electricity (LCoE), contrarily to CSP plants with capacity >100 MW, which provide LCoE < 20 cEUR/kWh. The integration of solid-state converters within CSP plants can enhance the scalability and economic competitiveness of the whole technology, especially at smaller scales, since the conversion efficiency of solid-state converters weakly depends on the size. Here a system with a high-temperature thermionic energy converter (TEC), together with an optical concentrator designed to be cheap even providing high concentration ratios, is proposed to improve the cost-effectiveness of CSP plants, thus achieving conditions for economic sustainability and market competitiveness. This is possible since TEC can act as a conversion topping cycle, directly producing electricity with a possible conversion efficiency of 24.8% estimated by applying realistic conditions and providing useful thermal flows to a secondary thermal stage. Under established technical specifications for the development of optical concentrator and TEC and according to reasonable economic assumptions, the overall plant conversion efficiency is estimated to be 35.5%, with LCoE of 6.9 cEUR/kW and considering the possibility of an 8 h storage tank for a 1 MW input solar energy system. The calculated projected value is an extremely competitive value compared with other available renewable energy technologies at small capacity scales and opens the path for accelerating the deployment of technological efforts to demonstrate the proposed solution.