Investigation of a hybrid renewable-based grid-independent electricity-heat nexus: Impacts of recovery and thermally storing waste heat and electricity

Abstract

Hybrid renewable energy systems meeting tight reliability constraints often generate a substantial quantity of excess energy, which if not utilized ultimately gets wasted. This study focuses on stand-alone energy systems meeting both electric and thermal loads. It compares a baseline (simplistic) scenario in which an equivalent electrical load is solely used to meet both electrical and thermal demands to three others: (i) gas-fired boiler to meet base thermal load (no thermal energy storage) and two others, both of which include thermal energy storage, namely (ii) recovering and storing the waste heat from the micro gas turbine's exhaust and the excess electrical energy, and (iii) recovering both quantities but storing only the waste heat. Systems modelled include solar photovoltaic, wind turbine, micro gas turbine, and lithium-ion batteries, all of which are conceptually modelled and optimized by a non-dominated sorting genetic algorithm-II using MATLAB.Results indicate that whilst appreciable improvements to the cost of energy can be achieved in all the three alternate scenarios compared to the (simplistic) baseline (0.22$/kWh at 3,976 kg/yr of carbon footprint, and 99% renewable fraction but dumping 564,130kWh/yr), integrating thermal storage and excess energy (electrical, thermal) recovery gives improved overall renewable fraction and carbon footprints. Out of the three alternate scenarios considered, the thermal energy storage integrated scenario that stores both excess electrical and thermal energy (waste heat) appears to be the best at a cost of energy of 0.166$/kWh, 25,220 kg/yr of carbon footprint, and 92.85% renewable fraction, with the potential of using all excess energy (0% dumped).