Proposed solar Rankine cycle system with phase change steam accumulator and CPC solar collector

An advanced solar thermal electric system with CPC (compound parabolic concentrator) collector and steam accumulator of phase-change type was newly proposed. The electricity generation efficiency of the proposed system using water vapor as the working fluid is estimated to be about 16 percent, which is about three times better than that of photovoltaic (PV) cell (about 67 percent) under a summer time operation. The total efficiency of the present system including space heating/hot water supply exceeds 60 percent. It will be shown that the electricity generation efficiency exceeds 21 percent if the working fluid were replaced with organic fluid like R-113(C₂Cl₃F₃). First, the present authors describe how to improve the thermal efficiency of the CPC collector. A lot of improvements were done including double glazing filled with Krypton gas, high temperature insulations, and selective coating. The developed CPC has the best thermal efficiency (for ex. 50% at TII=0.14) in the world including evacuated collectors. Second, the phase-change steam accumulator with high temperature phase change material (PCM) is designed and evaluated both experimentally and theoretically. The present steam accumulator has twice as better performance as the conventional sensible heat accumulator. Third, the new steam turbine (expander) is invented and designed based on "the concept of superposition (COS)". The proposed steam turbine consists of numerous thin disks of the same diameter with blade elements. The steam is introduced from a nozzle to this turbine with pulsating flow. This unique steam turbine is cost effective and can be easily extended to incorporate "cascading". The present paper reports experimental results of the proposed system under actual solar radiation and under heat stored accumulator condition. Further, it will be shown that the proposed solar Rankine cycle system has triple times better electricity generating performance than the current PV systems.