A prototype PEM-electrolyser has been designed and built for operation in distributed renewable energy systems, as part of a joint R&D project by Hydrogen Technologies and Institute for Energy Technology (IFE). The project (“REELYPEM”) was co-funded by the Research Council of Norway. The transient thermal and electrical behaviour of the PEM-electrolyser stack was studied and characterised. The PEM-electrolyser was tested for more than 1000 operational hours, with a nominal hydrogen production capacity of approximately 1 Nm³/h at 1 bar. The power input was an actual 3-day wind power profile, scaled to fit the maximum performance of the electrolyser with a time resolution of 1 second. The wind power profile was based on actual measurements taken from a test station for wind turbines at Valsneset in Norway, and represented a typical period with both maximum and minimum power from the wind power generator. In the experimental set-up at IFE the emulated wind power was fed directly to the electrolyser via a commercial electric vehicle battery tester, enabling hydrogen production from 0 to 100% of the rated electrolyzer capacity. The 3-day wind power profile was then cycled continuously to evaluate the performance of the electrolyser. The preliminary results indicate no statistically significant performance degradation for the first 500 hours of operation during the wind power input.