In this study, an exergy analysis has been done to show the effect of using a small fan on the exergy efficiency in a pyramid shaped solar still. The experiments were carried out in both seasons of summer and winter and also two different water depths to examine the effect of the solar radiation and water mass in the basin on the exxergy efficiency. The tests for the solar stills include the active (equipped to the fan) and passive units were performed under the climate condition of Mashhad (36° 36′ N), Iran. The results are presented for 2typical days in summer and 2typical days in winter. The results show that in the summer active unit has higher exergy efficiency rather than passive one while there is no considerable difference between the exergy efficiency of the passive and active units in winter. It was found that in summer the exergy efficiency is higher in comparison with winter. Also, the results show that the exergy efficiency is more where the water depth is less. Finally, an economic analysis has been conducted to estimate the productive cost of one liter fresh water by the passive and active solar systems. It was concluded that using a fan with negligible cost results in 8-9% decrement in the productive cost of fresh water.

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