Performance improvement of solar energy-based transcritical CO2 Rankine cycle utilizing a regenerator and energy storage tank

For the past decades, scientists have focused research into generating electricity from low-temperature resources like low-grade solar collectors, geothermal energy, and waste heat. Transcritical carbon dioxide (CO2) Rankine cycle can be used to extract energy from low-temperature heat resources. CO2 can be directly compressed to supercritical pressures and heated to its supercritical state before expanding to create a better thermal match with the heat resource due to its low critical temperature (31.98°C) and pressure (7.377MPa). The perfect temperature-shift matching enables the temperature curves between CO2 and the heat resource to be almost parallel, thus avoiding pinch point-related constraints and resulting in smaller exergy destruction. In this context, interest in transcritical CO2 Rankine cycles has been increasing recently to reduce the irreversibility of the heating process. CO2, which is an environmentally friendly natural fluid, has many special advantages like no ozone depletion and low global warming potential with attractive thermo-physical properties. In this study, energy and exergy analysis of the solar-based heat recovery transcritical CO2 Rankine cycle was carried out and compared with the experimental set installed at Doshisha University, Kyoto, Japan. The effects of a regenerator and an energy storage tank were theoretically analysed for the performance improvement of the transcritical Rankine cycle.