The first building-integrated photovoltaic system (BIPV) in Hong Kong has been working successfully for three years, as remote system for the first year and grid-connected system in the last two years. A number of issues have been investigated on the experimental system including technical, economical, operation and management topics. This paper presents the findings from this research project funded by the Industrial Support Fund of the Hong Kong SAR Government. Simulation and data monitoring have been completed for energy performance of the BIPV system under Hong Kong weather conditions. The natural ventilation effect of an air gap on PV module's power output and heat transfer across the PV wall and PV-roof have been investigated. Good agreement between simulation and experimental results was achieved. The system can provide about 41% of electric power for an indoor lighting floor area circuit of 250 m(2). The harmonics of the power output from the PV system was also measured to check the interference level to the utility grid. Experiments show that the total harmonics current distortion of the grid-connected BIPV system is far lower than that from some conventional equipment, such as personal computers. The total harmonics from this BIPV system is less than 12% for most of the time, even when the incident solar irradiation is very weak. (C) 2003 Elsevier Ltd. All rights reserved.