Thermodynamic analysis of a Carnot battery unit with double exploitation of a waste heat source

Abstract

Carnot batteries are critical technologies for increasing the penetration of renewable energy sources because they enable suitable energy storage for long-term periods. The achievement of a high round-trip efficiency is an important point that determines the sustainability of the Carnot batteries. In this direction, the present work comes to investigate a Carnot battery with latent storage that exploits properly a waste heat stream. The examined unit includes a high-temperature heat pump, an organic Rankine cycle, a latent storage system and the proper heat exchanger for the waste heat stream exploitation. The novelty of the studied idea lies in the exploitation of the waste heat stream in two ways. Specifically, the waste heat stream feeds firstly the latent storage system with heat, and secondary it feeds the evaporator of the heat pump with heat input for enhancing the heat pump’s coefficient of performance. This design makes it possible to achieve high round-trip efficiency values and also to exploit properly a waste heat stream. For the benchmark scenario with 100 kW electricity input, 350 kW waste heat input at 200 °C and 160 °C storage temperature, the round-trip efficiency was found at 64 %, the system’s energy efficiency at 14.2 %, the system’s exergy efficiency at 36.7 % and the produced electricity at 64 kW.