This' paper summarises I year of monitoring of a roof-mounted 1-kWp grid-connected system in Warsaw. The system has been in operation since December 2000. The PV array consists of 20 Millennia MST-50 MV modules. Climatic and solar radiation conditions at the site are reviewed, and the performance of the system is assessed from a component perspective (PV array, power conditioning unit) and from a global perspective (AC power delivered to the grid, system efficiency and system reliability). The performance of the system exceeded computer simulation expectations. The annual system energy yield is about 830 kWh, and the performance ratio ranges from 0.6 to 0.8. The efficiency of the PV system is in the range of 4-5%. The installed PV system plays an important role in demonstration and education.