Analytical expression for instantaneous exergy efficiency of a shallow basin passive solar still

An expression for instantaneous exergy efficiency of a passive solar still has been developed. The effect of design, operational and climatic parameters, namely effective absorptivity of basin liner (0.9–0.6), glass cover tilt (15–45°) and wind velocity (0.0–10 m/s) have been taken into account. It is found that with decrease in absorptivity (0.9–0.6) with time, the energetic and exergetic efficiencies decrease by 21.8% and 36.7% respectively. The effect of glass cover tilt is found to be insignificant and the respective efficiencies decrease by 0.75% and 0.47% per degree increase in tilt. These efficiencies increase rapidly up to a wind velocity of 2 m/s.

► The work is based on water purification technology.
► Simplified expression has been developed to predict the instant exergy efficiency.
► Exergy efficiency of solar still in different operating and climatic parameters can be obtained.
► Possible improvement in design for better exergy efficiency has been predicted.