Design and analysis of an innovative concentrated solar power system using cascade organic Rankine cycle and two-tank water/steam storage

Highlights: • Combination of cascade organic Rankine cycle and two-tank storage is novel. • Technical challenges associated with wet steam turbines are overcome. • Stable power output is guaranteed over a wide range of solar radiation. • A cycle efficiency of 27.4% is achievable at a hot tank temperature of 250 °C. • The system is potentially more cost-effective than a conventional DSG plant. Direct steam generation (DSG) solar power systems have the potential to improve heat collection performance and reduce capital cost. One challenge of the DSG solar thermal power technology is the unsteadiness of steam generation and power conversion under fluctuating solar radiation. A novel concentrated solar power generation system is proposed. It has three features: two-phase water/steam as heat transfer fluid, two-tank water storage, and cascade organic Rankine cycle (CORC) with a mixing chamber as power block. Steam is produced in the solar field and condensed in a high temperature tank, while an organic fluid replaces water for power conversion. The system enables smooth cycle operation by resilient control strategy and can tackle the challenge associated with wet steam turbines. It can tolerate lower purity of water/steam that only serves as the heat transfer fluid, thereby reducing the technical requirement. Thermodynamic performance in the normal operation condition and heat discharge process are assessed. The influences of ORC working fluid and storage tank size are examined. Results indicate that the mixing chamber temperature plays a crucial role in thermal efficiencies of both charge and discharge processes, storage capacity, and overall performance. A CORC efficiency of about 27.4% is achievable. The equivalent heat-to-power efficiency ranges from 13.35% to 18.81%, depending on the ORC fluid and volume of the storage tank. The novel system has an efficiency comparable to a conventional DSG system while a lower technical requirement in heat collection and power generation.