Testing method for thermal performance based rating of various solar dryer designs

► No load experimental study of various solar dryer designs has been performed. ► Non-dimensional parameter named no load performance index (NLPI) is identified. ► A thermal test method based on steady state heat balance concept is proposed for computation of NLPI. ► Invariable NLPI values are obtained for a wide range of parameters investigated. ► NLPI facilitates performance comparison of different dryer designs on equitable basis.