I have built and used Solar stills in semi arid environments as part of survival training courses. 1) You really need something that contains water in the pit under the plastic. 2) It takes several hours to produce just a little water. 3) They are annoyingly slow and inefficient.
It would take more energy to speed the process up (more area with more solar irradiance or an alternative heat source). Lots of people have put some thought into this but I suppose they could have overlooked something or missed an application specific opportunity (e.g. using waste heat from some other process).
https://www.research...solar_distiller
Edited by ckent323, 27 November 2018 - 12:48 AM.