Speed of reaching the full potential heat capacity of a basalt product: Mathematical model based on experimental results

Abstract

Renewable Energy Sources naturally deliver energy intermittently, causing fluctuations in energy supply. The energy is thus not provided corresponding to the actual need. With the increasing utilization of renewable energy sources, and according to energy availability, the demand for energy storage is rising. Energy storage tackles these growing problems and is therefore inevitable for a sustainable energy supply. Carnot batteries are one out of a few geographically independent storage possibilities for longer durations. A Carnot battery works in the way that electricity is stored in heat during times of overproduction and reconverted back to electricity when needed. This work focuses on the charging model of natural and cast basalt for packed bed thermal energy storage used in Carnot batteries. A mathematical model, based on experimental data of the speed of reaching the full potential heat capacity, is presented. It describes in a novel way, based on the change of heat capacity during heating and cooling, the charging and discharging behaviour of the material, independent from a possible storage layout. The model is a 4th-grade polynomial, well fitted to the data with the method of least squares.