For a smooth transition from fossil fuels to renewable energy sources and consequently a low-carbon society, we need reliable forecasts of wind speed and wind power, solar irradiation or solar energy. The weather forecasts enable us to plan the operation of wind, solar or combined power plants and integrate energy generated from renewable energy sources into the power grid. For the preparation of quality weather forecasts, their verification is crucial to help us understand the shortcomings of prognostic models and develop procedures for their improvements. The aim of the master's thesis is to verify whether prognostic models better predict the production of energy of the combined power plants or energy generated only from wind farms, or only from solar power plants. In northern Germany, five sites of wind parks and weather stations with pyranometers were selected. Three sites are located in the vicinity of the sea, two in the interior of northern Germany. With different sites of combined power plants, we investigated how the proximity of the sea affected the amount of wind energy produced because wind speed on coastal areas is higher. The predictability of wind speed and wind power is affected by how well a model describes processes in the boundary layer. The forecast verification of wind speed and wind power, solar irradiation and solar energy of the ECMWF model showed that the predictability of solar irradiation or solar energy was better than the predictability of wind power. We also compared the WRF model downscaling analyses with wind speed and solar irradiation measurements. The WRF model downscaling analyses errors were higher than the ECMWF model forecasts errors since the WRF model does not have its own data assimilation. It is essential that data are assimilated in a high-resolution model. A thorough comparison of the measurements and forecasts or downscaling analyses was carried out for only one location. Based on the results of combined power plants which are located in different sites, we saw that the predictability of energy production of the combined power plant for four out of five sites considered was better than the predictability of wind power generation. When we verified the forecasts of wind and solar energy production, we observed a daily cycle of error. The predicted errors of combined energy were lower because solar and wind energy are interdependent over time.