This work aims at analyzing and architecting natural and artificial parameters to model a water-film cooling system for photovoltaic modules for some months under warm conditions. Methodologically, the theoretical and technical aspects were structured to develop, implement, monitor, and assess the cooling system at an on-grid, outdoor testing unit, considering the following: (i) the criteria to select and to approve the implementation site (infrastructure and climatologic and solarimetric conditions); (ii) the types, frequency and qualities of the monitored data; (iii) the system measurement, monitoring and control equipment; (iv) the commissioning of the system as a whole; and (v) the tests and results empirically obtained. The water-film cooling system reduces the temperature by 15−19%, on average, and up to a maximum of 24−35%. In terms of electric power, there was an average gain of 5−9% at the time of day with the highest solar radiation, and maximum gains of 12% on days with solar radiation above average. Regarding gross energy, average gains of 2.3−6%, and maximum gains of 6.3−12%, were obtained. It was concluded that the test unit helps understand the natural phenomena and the development, operation, and maintenance of performance gain systems of on-grid PV modules for construction on a commercial scale.