Cascade Latent Heat Storage for Solar Cooking Applications

Abstract

The present investigation explores the potential of multiple phase change material (PCM) based storage for real-time solar thermal applications. There are two types of storage configurations tested in this work for the simultaneous charging and discharging operation, i.e., single PCM-based NaNO3 storage and 2-stage cascade latent heat storage having NaNO3 and NaNO2 as the storage mediums in the consecutive stages. The storage is designed to achieve the end-use temperature condition of 513 K (the highest temperature required for cooking) with the latent thermal energy accumulation capacity of 1 MJ. The study envisages that instead of using a single PCM in the storage unit, 2-stage cascading of the PCMs can improve energy accumulation and retrieval in storage. After 8 hours of operation, none of the storage achieves the complete charging state. The energy accumulated in the NaNO3/NaNO2 cascade storage is found to be 2.6 times higher than the energy accumulated in the NaNO3 storage. NaNO3/NaNO2 storage achieves the desired constant outlet temperature of cold heat transfer fluid for chapati making (531 K) after 165 minutes of operation. At this moment, the latent energy accumulated in the NaNO3 and NaNO3/NaNO2 storage is observed as 35% and 14%, respectively