The share of photovoltaic (PV) power in Switzerland is expected to rise during the next decades in response to legal requirements on renewable energy production and energy efficiency. In order to assure constant transition network stability, balance groups are obliged to predict the expected amount of power produced by their PV plants (and automatically fed into the transition network) for every following day in a 15 min-resolution. Due to the strong dependency of PV power production on weather, numerical weather prediction (NWP) models can be used as a basis for day-ahead PV power production forecasting.