Field-test data from a 50 kW photovoltaic (PV) system installed at The Nara Institute of Science and Technology (NAIST) were analyzed in detail. We found that the PV system operated in a wide temperature range and was strongly affected by the temperature coefficient of conversion efficiency when the module temperature became high. The temperature coefficient dependence of the system performance was analyzed in order to estimate the annual output of the system in an actual operating environment. As a result, it was found that the annual output energy of the PV system increased about 1% by an improvement of 0.1%/degreesC in the temperature coefficient. This result indicates that it is very important to consider the temperature characteristics in solar cell development. (C) 2002 Elsevier Science B.V. All rights reserved.