This paper is about predicting the average conventional energy conversion by a photovoltaic system in Malaysia. The calculation is based on average number of days in a month. Average hourly energy flows are estimated based on knowledge of array test parameters, monthly average of hourly ambient temperature and monthly average of daily hemispherical radiation. The monthly average of diffuse component of radiation can be predicted based on hemispherical radiation, by using an appropriate empirical correlation related to the monthly average of diffuse fraction to monthly average of clearness index. The values of hourly average radiation are estimated based on a statistical model. (C) 2003 Elsevier Ltd. All rights reserved.