Enabling rating of intermediate temperature solar cookers using different working fluids as test loads and its validation through a design change

Solar cookers working at intermediate temperature (120–240 ˚C) promise faster propagation of solar cooking technology as they offer a range of cooking options with reduced cooking time. As the thermal losses in such cases would be relatively high, it is pertinent to develop an appropriate rating technique. This paper attempts to identify and investigate the suitable test loads that enable the selection/rating of different designs of solar cookers at intermediate temperatures. Thus, two different working fluids have been used as the tests loads. Two different designs of solar cookers have been tested to serve the purpose using Cooker Opto-Thermal Ratio (COR) as a thermal performance parameter (TPP). The experimental results show that the use of proposed test loads yields approximately identical value of TPP for a specified design of solar cooker at intermediate temperature and enables its rating/grading at such temperatures. The impact of design change at an intermediate temperature on the TPP has been assessed by changing the radiative characteristics of the cooking pot surface to validate the proposal. It is observed that in the case of concentrating solar cooker the design change has a large impact on the TPP value and accordingly the maximum achievable cooking temperature and reference time show substantial improvement. However, in a box type cooker, the impact of design change is seen to be insignificant.