Investigation of the Effect of Cycling on the Performance of Packed Bed Solar Energy Storage System

Packed bed thermal energy storage system is an important component of solar energy conversion system. Conventionally packed bed systems have been designed on the basis of the thermal energy considerations only. Charging and then discharging of bed complete one cycle. It has now been realized that in cycling process special attention needs to be paid to the design to take into account the energy losses as well as the maximum utilization of available energy. In this work, an investigation has been carried out on the effect of cycling (charging and discharging cycle) on the performance of packed bed solar energy storage system. Temperature profiles during charging and discharging have been determined. It has been found that during finite time discharging, the bed cannot be fully discharged and certain amount of unused energy still remains entrapped in the bed. Stabilized unused energy has been found which has been seen to be strongly affected by the bed parameters, namely, the element size and shape, void fraction and aspect ratio of the bed. The values of these parameters to result in minimum value of this stabilized unused energy have been found within the range of investigation. It has been found that unused energy can be minimized by keeping element size to be small and by using highly non spherical elements combined by high void fraction and large aspect ratio of the bed.