Carnot battery application in a parabolic trough concentrating solar power plant: System modelling, validation and analyses on the interplay between stored energies

Abstract

A Carnot battery application in a conventional parabolic trough concentrating solar power (CSP) plant is examined. During solar thermal charge cycles, electric heaters import renewable energy (RE). This is stored as thermal energy in the plant’s storage system, thereby boosting solar thermal charge cycles. The plant discharges stored thermal energy to support baseload power generation and RE time-shifting. A computational model of the system is developed and validated as reasonably accurate. This is used to investigate potential interplays between stored solar thermal energy and imported RE within the Carnot battery. Results show that for certain storage capacities, solar multiples, heater capacities and heater set-point temperatures, imported RE is stored at the loss of solar thermal energy. Such configurations overcharge storage with imported RE, thereby curtailing solar thermal energy unnecessarily. This leads to operational trade-offs within the CSP Carnot battery, which are not thoroughly assessed in the literature. Via parametric analyses, the paper demonstrates the usefulness of the plant utilisation factor (UF, a less common CSP metric) in measuring the dynamics and magnitude of thermal energy storage (TES) overcharge. The paper develops fundamental insights from the aforementioned design variables, for practical applications in CSP Carnot battery designs that aim to mitigate solar thermal curtailment. Key findings show that: (1) “tipping points” of UF provide constraints on maximum heater capacity to avoid TES overcharge; (2) heater and TES capacities are negatively correlated at the onset of TES overcharge; (3) sufficiently small TES capacities can mitigate overcharge entirely; (4) TES overcharge is aggravated by higher heater set-point temperatures; (5) smaller sized parabolic trough solar fields reduce and delay solar thermal curtailment from heater integration.