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 worldwide in a renewable and sustainable manner. Solar organic Rankine cycles (SORCs) 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. Improvement in efficiencies of components has a cascading benefit in the performance of SORC, operating costs, and payback period. A comparative energy and exergy analysis study is performed to assess the thermodynamic performance of subcritical non-recuperative solar organic Rankine cycle 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. Variations of optimal mass flow rate values with respect to time and ηI, ηII with respect to heat source temperatures are plotted. In all, the energy efficiency of the overall system remained almost the same, when the proposed system is operated at the exergy-based vs energy-based optimal operating conditions. However, 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.