Reliable knowledge on the performance of different photovoltaic generators (as single cells, modules, laminates, shingles, car roofs, etc.) under actual operating conditions is essential for correct product selection and accurate prediction of their electricity production. For this purpose, an outdoor test facility was erected at the Paul Scherrer Institute, PSI. It consists of a sun-tracked sample holder, electronic loads and a PC-based measuring system. Insolation is measured with pyranometers, pyrheliometers and reference cells. Characterisation of a generator under given test conditions means the precise acquisition of its electrical behaviour under varying load. The generator＇s efficiency and all the relevant electrical parameters are derived on-line from a series of measured current/voltage (I/V) values. I/V-scans at constant insolation and at different generator temperatures enable the temperature coefficients of the efficiency and the electrical parameters to be determined. Thereafter I/V-scans at different insolations (10-1200 W/m(2)) and air masses (1.1-5) yield (via temperature correction) the insolation dependence of the efficiency at constant temperature. A complete scan takes about 5-15 s. Samples of size varying from 1 by 1 mm up to 1.5 by 1 m can be tested at currents up to 32 A and at voltages up to 120 V. For modelling purposes, the results are represented in the form of correlations, e.g. the efficiency as a function of the operating parameters temperature, insolation and air mass. Results obtained in PSI＇s test facility were confirmed by the Fraunhofer-Insitut fur Solare Energiesysteme, D-79100 Freiburg, Germany. Measurements are presented from some modules and single cells as well as some efficiency correlations. Results are also presented on lamination losses, on PSI＇s high efficiency cell, on Gratzel cells and watch modules as well as on shading effects and of a small thermophotovoltaic generator.