In this Application Note, a versatile and reliable measurement system for photoelectrochemical investigations is described which aims to assist scientists in obtaining reproducible photoelectrochemical data of high quality, including the solar-to-hydrogen (STH) efficiency. Specifically, it addresses the parameters irradiation quality, reaction temperature and gas measurement. The setup is designed to exclude stray light and uses a solar-grade mirror to reflect the light of a vertical solar simulator on the electrochemical cell. The light quality in the setup (»AAA«, IEC 60904-9) is close to the classification of the solar simulator itself. The temperature in the electrochemical cell is controlled with an external Peltier element and can be kept constant in the range of 20–45 °C. The influence of reaction temperature on the photocurrent of a WO 3 photoanode is demonstrated. The gaseous reaction products are analyzed with a mobile gas chromatograph, using an automated measurement routine with discontinuous sampling from the electrochemical cell. The system is applied to determine the Faraday and STH efficiencies of a copper indium gallium selenide photocathode.