Adding wind power generation in a power system changes the operational patterns of the existing units due to the variability and partial predictability of wind power production. For large amounts of wind power production, the expectation is that the specific operational costs (fuel costs, start-up costs, variable operation and maintenance costs, costs of consuming CO2 emission permits) of the other power plants will increase due to more operation time in part-load and more start-ups. The change in operational costs induced by the wind power production can only be calculated by comparing the operational costs in two power system configurations: with wind power production and with alternative wind production having properties such as conventional production, that is, being predictable and less variable. The choice of the characteristics of the alternative production is not straightforward and will therefore influence the operational costs induced by wind power production. A method is applied for calculating the change in operational costs due to wind power production using a stochastic optimisation model covering the power systems in Germany and the Nordic countries. Two cases of alternative production are used to calculate the change in operational costs, namely perfectly predictable wind power production enabling the calculation of the costs connected to partial predictability and constant wind power production enabling the calculation of the operational costs connected to variability of wind power production. A 2010 case with three different wind power production penetration levels is analysed.