Developing a test standard/protocol for solar box type cookers has drawn a considerable interest among the researchers throughout the world. Recent publications on solar cookers emphasize the need of introducing the thermal performance indicators determined through exergy analysis. In the present paper, the time variation of instantaneous exergy output and energy output as function of its temperature and also of the instantaneous ambient temperature have been reported for truncated pyramid type solar box cooker and compared with those of box type cooker. Further, variations in the exergy lost with temperature difference have been depicted for the selected water temperature range from 60 degrees C to 95 degrees C. Based on this study, quality factor, exergy temperature difference gap product, and heat loss coefficient are determined and are proposed as benchmark parameters of solar cooker's thermal performance. (C) 2011 Elsevier Ltd. All rights reserved.