English: An example of a condenser-on-roof installation , condenser made of plastic film with special properties, with insulation layer between film and concrete roof surface. This installation is on school buildings at Sayara ( Kutch , India). Unlike the metal roofs that attract some condensation without any treatment , the concrete roofs do not. Hence the need for an external condenser. The output from such condensers is nearly two times higher than from bare metal roof , every thing else remaining constant.