A comparison of erythritol and erythritol mixed with granite as heat storage materials in solar cooking experiments

Solar storage cooking pots enable storing heat during non-sunshine hours. Latent heat provides the best storage option for greater energy storage density; however, it is expensive for large storage volumes. A reasonable option to reduce the cost of latent heat storage is to combine latent heat storage directly with sensible heat storage in a mixed storage system. This paper aims to compare a pure latent heat storage system (erythritol) with a mixed storage system consisting of equal mass ratios of erythritol and granite pebbles (5-10 mm) for a solar cooking application. Two small black stainless cooking pots with a capacity of 1 litre are placed inside two larger 5-litre cooking pots to make simple storage cooking pots. The space between the pots is filled with thermal energy storage (TES) material. 2.0 kg of erythritol is filled in the space between the pots in the first configuration. The second storage configuration consists of 1 kg of erythritol and 1 kg of granite pebbles in the space between the pots. The first experimental tests involve charging the storage cooking pots without any load for 4 hrs and then discharging the pots using heating loads in insulated wonderbags to evaluate the off-sunshine cooking performance for 4 hrs. The second experimental test involves charging the storage cooking pots while simultaneously cooking and storing heat in alternative charging and discharging cycles. Experimental results show that higher temperatures are achieved by the mixed storage system compared to the erythritol storage system during charging without any cooking taking place. For discharging cycles, the heat utilisation rate is faster for the mixed storage system than for the erythritol storage system. It is possible to cook multiple meals for both storage systems in an 8-hour cooking period. The erythritol storage system showed higher temperatures than the mixed storage system at the end of the experimental tests, suggesting that the erythritol storage system was more efficient during heat utilisation. The two configurations can cook rice, vegetables, and chicken within an hour during heat utilisation (discharging) tests.