This paper deals with a series of tests conducted on a PV-DC pump. The tests involved measurements of solar radiation, on both a horizontal surface and the tilted module surface, flow rates, volumes, and total dynamic heads. In total, up to 3000 data were collected every day whose analysis allowed the authors to find empirical relationships between system efficiencies, solar radiations and total dynamic heads. The second part of the paper develops a simple method that allows both the assessment of performances of the whole system when installed in a different site from that in which the tests were performed and the optimal inclination angle of the panel to be determined in relation to annual or seasonal use.