Abstract This paper describes an analytical methodology for the optimised design of stand-alone photovoltaic (PV) systems installed at locations where the solar radiation is considerably shortened by obstacles, i.e. at the bottom of a gorge. A method for the computation of the real available solar energy incident on the PV panel is proposed, based on easily conducted measurements. The optimum tilt of the PV array, under such conditions, is obtained and a dimensioning procedure provides the optimal size of the PV-array/storage. The resulting system is tested by a verification routine. A case study, employing the complete algorithm proposed, is illustrated.