A novel concentrated solar power system using cascade steam-organic Rankine cycle and two-stage accumulators

A novel direct steam generation solar power system is proposed based on steam screw expander, cascade steam-organic Rankine cycle (SORC) and two-stage accumulators. The high temperature accumulator (HTA) enables smooth power conversion and stores thermal energy when solar radiation is available. The low temperature accumulator (LTA) is employed to elevate the storage capacity. One of the most remarkable features of the system is the heat discharge mode. First, heat is released via water vaporization in the HTA to drive the SORC. A maximum HTA temperature drop about 20 °C can be permitted. Then water at reduced temperature flows from the HTA to the LTA and heat is only used to drive the organic Rankine cycle (ORC). Nine organic fluids are adopted to analyze the system performance for seven regions worldwide. The results indicate that, compared with a conventional single-stage accumulator, the LTA can increase the storage capacity from 1.0 MWhe to 8.4 MWhe. The equivalent payback time in regard to the additional accumulator and collectors is estimated to be around 5 years in Phoenix and Lhasa. The LTA has great potential to improve the cost-effectiveness of the whole system.