The tilt angle influences the amount of energy collected by a photovoltaic module. However, representations of these effects on the energy yield and the performance of the PV system are commonly based on the theoretical calculations, whereas there is a lack of experimental investigations. To verify the calculations, an experimental setup has been installed at the Department of Electrical and Computer Engineering, University of Tehran. Some results of this test station, from March, 1999 to January, 2000 are represented in this paper.