Multi-dimensional comparison and multi-objective optimization of geothermal-assisted Carnot battery for photovoltaic load shifting

The urgent need to address the tight energy and environmental situation has compelled scientists to seek novel conversion and storage technologies that can effectively handle the unpredictability and intermittency of renewable energy, to advance the reformation of the world energy framework. Therefore, this study develops four efficient geothermal-assisted Carnot batteries for storing and transferring renewable energy power. Initially, the mathematical models of the four Carnot batteries are established and validated by means of design parameter and published literature data. Subsequently, a series of studies, including multi-cycle performance comparison, multi-dimensional running conditions analysis, and multi-objective optimization are executed. Later on, the performances of each subsystem and equipment are thoroughly investigated under the optimal running condition. Eventually, the benefits of geothermal-assisted and the practical application potential of the Carnot batteries are deeply assessed. The numerical results reveal that the transferred power, heat-to-power efficiency, exergoeconomic factor, and exergoenvironmental factor of these Carnot batteries reach 78.14 kW, 137.16%, 55.06%, and 0.833%, respectively, and the heat-to-power efficiency is improved by 20.54–85.73% compared with similar Carnot batteries, demonstrating excellent performances in thermodynamic, exergoeconomic, and exergoenvironmental. This study fully utilizes multi-form renewable energy, in line with carbon neutrality and energy saving requirements, and can offer valuable guidance to scientists who are working on renewable power storage and transfer, as well as exergoeconomic and exergoenvironmental assessments.