Thermal performance of latent heat energy storage system with/without enhancement under solar fluctuation for Organic Rankine power cycle

Abstract

Thermal energy storage (TES) is an effective method to buffer solar fluctuation and enable Organic Rankine Cycle (ORC) to operate under steady and design conditions. Heat transfer and energy storage characteristics of TES systems under solar fluctuation need to be studied to better understand the practical energy storage process and provide guidance on design/optimisation of integrated TES-ORC systems. In this paper, the charging process of a shell-and-tube system containing molten salt as phase change material with/without ceramic foam enhancement over a whole sunny and cloudy day was investigated. For the same full charging cases, the total stored energy is different according to solar fluctuation, with a maximum difference of 17.9%. Strong solar radiation not only accelerates the energy storage rate but also improves the total stored energy. Rising solar radiation can also cause large total stored energy while the energy storage rate is slow. Oscillating solar radiation generates the least total stored energy among full charging cases, however, the energy storage rate is higher than that under rising solar radiation. Falling solar radiation leads to small total stored energy. Ceramic foam-enhanced molten salt is more sensitive to solar fluctuation while the total stored energy over the whole working day is improved by 33.2% on a sunny day and 29.1% on a cloudy day respectively.