Box type solar cookers with sensible thermal energy storage medium: A comparative experimental investigation and thermodynamic analysis

Box type solar cookers with and without thermal energy storage are experimentally analysed within the scope of this research for characteristic continental climatic conditions of Bayburt, Turkey. For efficient and continuous cooking in such climates, thermal energy storage is required to be considered in solar cookers due to remarkable temperature differences between sunrise and sunset. Bayburt stone, a special natural stone with low density and notably high specific heat capacity, is utilised as a sensible thermal energy storage medium in a box type solar cooker, and thermal performance assessment of Bayburt stone cooker is compared with a conventional cooker without thermal energy storage through a comprehensive experimental research and thermodynamic analysis. For a typical late summer day, solar intensity, ambient temperature, absorber plate temperatures, internal air temperatures, internal and external glass temperatures, water temperatures, energy and exergy efficiencies are determined time-dependently for each solar cooker. The results clearly indicate that absorber plate temperature in conventional solar cooker has a notable decreasing tendency toward sunset, which totally affects the overall thermal performance of the system. On the contrary, Bayburt stone cooker enables an efficient, steady and continuous cooking till late evening owing to sensible thermal energy storage medium. In terms of thermo-dynamic performance figures, Bayburt stone cooker is observed to have considerably better energy and exergy efficiency. According to the results, energy efficiency of Bayburt stone cooker is determined to be in the range of 35.3-21.7% while it is found to be 27.6-16.9% for conventional solar cooker. On the other hand, exergy efficiency of Bayburt stone cooker is determined to be 21.2-14.1% whereas it is calculated to be 18.0-11.6% for conventional cooker. It can be concluded from the results that Bayburt stone as a thermal energy storage medium remarkably improves the thermal performance figures of box type solar cookers.