Use of Low/Mid-Temperature Solar Heat for Thermochemical Upgrading of Energy, Part I: Application to a Novel Chemically-Recuperated Gas-Turbine Power Generation (SOLRGT) System

This paper is the first part of a study presenting the concept of indirect thermochemical upgrading of low/mid temperature solar heat, and demonstration of its integration into a high efficiency novel hybrid power generation system. The proposed system consists of an intercooled chemically recuperated gas turbine (SOLRGT) cycle, in which the solar thermal energy collected at about 220 °C is first transformed into the latent heat of vapor supplied to a reformer and then via the reforming reactions to the produced syngas chemical exergy. The produced syngas is burned to provide high temperature working fluid to a gas turbine. The solar-driven steam production helps to improve both the chemical and thermal recuperation in the system. Using well established technologies including steam reforming and low/mid temperature solar heat collection, the hybrid system exhibits promising performance: the net solar-to-electricity efficiency, based on the gross solar thermal energy incident on the collector, was predicted to be 25–30%, and up to 38% when the solar share is reduced. In comparison to a conventional CRGT system, 20% of fossil fuel saving is feasible with the solar thermal share of 22%, and the system overall efficiency reaches 51.2% to 53.6% when the solar thermal share is increased from 11 to 28.8%. The overall efficiency is about 5.6%-points higher than that of a comparable intercooled CRGT system without solar assist. Production of NO_x is near zero, and the reduction of fossil fuel use results in a commensurate ∼20% reduction of CO₂ emissions. Comparison of the fuel-based efficiencies of the SOLRGT and a conventional commercial Combined Cycle (CC) shows that the efficiency of SOLRGT becomes higher than that of CC when the solar thermal fraction X_sol is above ∼14%, and since the SOLRGT system thus uses up to 12% less fossil fuel than the CC (within the parameter range of this study), it commensurately reduces CO₂ emissions and saves depletable fossil fuel. An economic analysis of SOLRGT shows that the generated electricity cost by the system is about 0.06 $/kWh, and the payback period about 10.7 years (including 2 years of construction). The second part of the study is a separate paper (Part II) describing an advancement of this system guided by the exergy analysis of SOLRGT.