Control strategy and performance of a small-size thermally integrated Carnot battery based on a Rankine cycle and combined with district heating

peer reviewed ; To encourage decarbonization and promote a widespread penetration of renewable energy sources in all energy sectors, the development of efficient energy storage systems is essential. Interesting grid-scale electricity storage technologies are the Carnot batteries, whose working principle is based on storing electricity in the form of thermal energy. The charging phase is performed through a heat pump cycle, and the discharging phase is conducted through a heat engine. Since both thermal and electric energy flows are involved, Carnot batteries can be adopted to provide more flexibility in heat and power energy systems. To this aim, efficient scheduling strategies are necessary to manage different energy flows. In this context, this work presents a detailed rule-based control strategy to schedule the synergetic work of a 10-kWe reversible heat pump/organic Rankine cycle Carnot battery integrated to a district heating substation and a photovoltaic power plant, to satisfy a local user's thermal and electric demand. The coupling of a Carnot battery with a district heating substation allows for shaving the thermal demand peaks through the thermal energy stored in the Carnot battery storage, allowing for a downsizing of the district heating substation, with a considerable reduction of the investment costs. Due to the multiplicity of the involved energy flows and the numerous modes of operation, a scheduling logic for the Carnot battery has been developed, to minimize the system operating costs, depending on the boundary conditions. To investigate the influence of the main system design parameters, a detailed and accurate model of the Carnot battery is adopted. Two variants of the reference system, with different heat pump cold source arrangements, are investigated. In the first case, the heat pump absorbs thermal energy from free waste heat. In the second case, the heat pump cold source is the return branch of the district heating substation. The simulation results show that, in the first case, the ...