Active multi-effect vertical solar still: Mathematical modeling, performance investigation and enviro-economic analyses

In this paper, year round performance and enviro-economic analyses of active multi-effect vertical solar still were carried out using the developed comprehensive mathematical model. The optimum number of effects, mass flow rate of feed water and gap between the effects were found to be five, 7.20 kg/h and 0.05 m, respectively. Maximum annual average distillate yield of 6.78 and 21.29 kg/m2-d was noticed for the optimized unit under normal mode and low pressure mode operation. Maximum annual average Performance ratio (PR) and Solar energy Coefficient of Performance (SCP) of 5.59 and 3.03 was noticed under evacuated mode operation. Energy payback time and distilled water production cost of the evacuated unit treating 5 wt% saline water was around 1.37 yrs and Rs.2272.00/m3 (33.00 USD/m3), respectively and it can effectively mitigate at least 81.81 tons of CO2 emission during its life time of 20 yrs. Distilled water production cost of the evacuated unit was found to reduce from Rs.2270.00/m3 (33.00 USD/m3) to Rs.1310.00/m3 (19.00 USD/m3) by decreasing the interest rate from 12% to 5%. Salinity of feed water and interest rate at which the unit was financed played a major role in distilled water production cost.