Economic evaluation was carried out to understand the main contributors to water production cost in solar-powered membrane distillation (SP-MD) systems. Three SP-MD systems (Direct Contact (DCMD), Air Gap (AGMD), and Vacuum (VMD)) were modeled and economically analyzed. A parametric study was conducted on the AGMD, the most frequently used SP-MD configuration, to understand the relationships between various design and operation parameters and water production cost. The parametric study results show that, in the AGMD system, increasing the feed inlet temperature had a significant effect in lowering the cost while higher feed flow rate resulted in increased water production cost. This study also shows that higher effective membrane length and lower air gap width and feed channel depth reduce the cost of water. Finally, the choice of MD configuration (AGMD, VMD, DCMD) in SP-MD systems will impact the final water cost. (C) 2012 Elsevier B.V. All rights reserved.