Applied Mathematical Model for Solar Energy Collection and Thermal Storage

Abstract

Solar thermal storage systems (STSS) are renewable energy systems that provide a continuous, controllable source of heat for many applications. The inherent variability of solar insolation poses a challenge to the use of direct solar power for continuous operations. A dynamic non-linear model of the STSS was initialised via a steady state analysis and verified by drying 1000 kg of cocoa beans per batch from 60% to 8% moisture content. Ambient temperature and insolation data for Trinidad in 2017 were used as inputs. This was achieved by modifying flow rates, varying aspect ratio of the storage tank, and observing their effect on storage tank temperature profiles and drying air temperatures. The steady state analysis determined the tank volume as 12.57 m3 and a required mass airflow rate of 1020 kg/h. A dynamic model of the STSS revealed an optimal tank aspect ratio of 2:4 m (D: H) and that three AE-40 solar collectors were sufficient. The effect of the circulation rate between the storage tank and solar collectors on energy storage was found to be negligible. The need for temperature control was demonstrated and a control strategy developed. A pilot plant was built using recommended specifications, albeit without temperature control. As predicted, drying was more than sufficient, but poor control led to burnt cocoa beans. The application of this work extends well beyond the cocoa bean test case, and the open-source models built can be applied to optimise the design of any solar heating application.