Modified Hottel-Whillier-Bliss Equation for an Active Solar Distillation System for Higher Yield and Thermal Efficiency

Based on energy-balance equations for a photo-voltaic thermal (PVT) active solar distillation system, a modified Hottel-Whillier-Bliss (HWB) analytical characteristic equation as a function of design and climatic parameters has been derived in the present article. It has been found that there is a significant difference between characteristic equations for PVT-based active solar distillation and the conventional flat plate collector (FPC). It is due to (i) opposite nature of loss factor from inside surface to ambient through glass cover and (ii) temperature dependence of the evaporative heat transfer coefficient between water surface and condensing cover in the solar distillation system. Numerical computations have been obtained for the characteristic curve of the proposed active solar distillation system and flat plate collector under the condition of a typical day in New Delhi, India. Further, the effect of performance parameters such as packing factor, electrical efficiency of individual PVT collectors, and water mass have also been studied for the proposed active PVT solar distillation system. Moreover, daily yield of portable water has been found to be 7.34 kg/m² at n = 5 and β_c = 0.25 which is 100.5% higher than the daily yield of 3.66 kg/m² obtained at n = 1, β_c. = 0.89.