The photovoltaic (PV) technology has made considerable progress during the recent years in both grid connected and stand-alone applications, especially in areas of high local solar potential. In this context, the interest recently demonstrated in the Greek region concerning PVs encourages the investigation of optimum operation conditions for such systems. At the same time, summer-only applications, being rather common in Greece, require maximum exploitation of the local solar potential during the specific period of the year. For this purpose, an experimental study is currently carried out in the area of Athens, in order to evaluate the performance of different PV panel tilt angles during the summer period. According to the experimental results obtained, the angle of 15 degrees (+/- 2.5 degrees) is designated as optimum for almost the entire summer period, while conclusions drawn are accordingly theoretically validated by means of established solar geometry equations. (C) 2011 Elsevier Ltd. All rights reserved.