Solar organic Rankine cycle—Parametric analysis based on exergy vs energy approaches

Abstract

Solar thermal electricity generation is one of the encouraging technologies for reducing scarcity of electricity in the world in a renewable and sustainable manner. Solar Organic Rankine Cycles (SORC) are sustainable and an eco-friendly means of power production at low and medium heat source temperatures. The proposed system includes a Parabolic Trough Collector based solar system, which operates with Therminol VP-1 oil, a two-tank direct thermal energy storage unit and an Organic Rankine Cycle (ORC) operates with a working fluid Toluene. Improvements in efficiencies of components has cascading benefit in performance of SORC, operating costs and payback period. A comparative energy and exergy analysis study is performed to assess thermodynamic performance of sub critical non-recuperative solar organic Rankine cycle (NR-SORC) on the basis of heat source temperatures and ORC operating parameters. Iterative procedure is adapted in the analysis to find optimal operating parameters to maximize efficiency. Maximum energetic and exergetic efficiencies of SORC are calculated at various optimal T5 and pevp. Variation of optimal mass flow rate values w.r.t time and ηI, ηII w.r.t heat source temperatures are plotted. All in all, the energy efficiency of overall system remained almost the same, when proposed system is operated at exergy based optimal operating conditions as against the energy based. But significant enhancement of 6.61% and 12.42% in exergetic efficiency of ORC and overall system respectively are observed when SORC operates at exergy based optimal operating conditions.