The evaluation and assessment of the performance of photovoltaic (PV) cells requires the measurement of the current as a function of voltage, temperature, intensity, wind speed and radiation spectrum. Most noticeable of these parameters is the PV conversion efficiency eta (defined. as the maximum electrical power P-max produced by the PV cell divided by the incident photon power P-in) which is measured with respect to standard test conditions (STC). These conditions refer to the solar spectrum (AM1.5), solar radiation intensity (1000 W m(-2)), cell temperature (25 +/- 2 degreesC) and wind speed (2 mph). Tests under STC are carried out in laboratory-controlled environment. With an increase of ambient temperature, there is a deficiency in the electrical energy that the solar cell can supply. This situation is especially important in hot climates. Outdoor exposure tests of solar cells have been conducted in the Department of Physics, University of Brunei Darussalam. Preliminary results demonstrate that the efficiency of the single crystal silicon solar cell strongly depends on its operating temperature. It has been noted that at the operating temperature of 64 degreesC, there was a decrease of 69% in the efficiency of the solar cell compared with that measured at STC. Investigation of the effect of variation in intensities of sunlight on the solar cell performance showed that the efficiency of the cell is reduced as intensities of sunlight are reduced but at a rate different from the reduction in intensities. (C) 2003 Elsevier Science Ltd. All rights reserved.