In this work we use the mean-variance portfolio optimization, using as input the power derived from the wind and density results of meteorological model simulations (ERA-Interim reanalysis), to minimize the variability of the wind power produced in a large region. The methodology involves selecting the placement of the wind farms on a high spatial resolution grid. We used the EU-28 region to check the method and perform sensitivity tests. We studied the influence of the ratio between the total installed power of the whole domain (P t ) and the maximum power that can be installed per cell (P mi ) on the variability of wind power yield. The results show that the reliability of the electrical system improves when P mi grows and worsens when P t grows. A quadratic fit relates the variability of the system and the aforementioned ratio. The optimization procedure tends to select groups of terrain cells where wind farms should be installed. These groups grow when more energy production is demanded of the system, but they roughly maintain their location. There is some evidence that in a larger region greater system reliability could be achieved. Most of the selected cells have either a high or a low capacity factor and those with the latter are crucial in enhancing system reliability. KEYWORDS electricity, Europe, MVP, planning, variability, wind energy 1 | INTRODUCTION In many countries, there has been a rapid development of wind energy. While a small amount of wind energy can be incorporated into the electrical system without difficulty, higher amounts of it generate problems in predicting how much energy has to be produced by other sources, mainly coal, oil, open-cycle gas turbines, combined-cycle gas turbines, combustible renewables and waste, and hydropower. 1 In addition, other undesirable consequences, such as difficulties for the grid or increased costs of secondary services, have already been identified and estimated. 2-4 While wind power prediction, mainly based on persistence and atmospheric models' predictions, helps in ameliorating the problem, a nonnegligible degree of uncertainty about the wind power that will be added to the electrical system still exists. It leads to instabilities in the electrical network and therefore limits the number of wind farms that it is desirable to have installed in a region. To compensate for that instability, a number of flexible resources (eg, dispatchable power plants and demand-side management) whose power output should be equal to the variability are required to cover it. 5 Therefore, to increase the amount of clean energy from wind power that is provided to the electrical network, either the number of flexible resources must also grow or the wind power variability must be reduced. The installation and maintenance of flexible resources increases the overall cost of energy. From the work of Roques et al 6 and Drake and Hubacek, 7 we know that variability of wind energy can be reduced by combining the power output of separate wind farms or countries in a powerful electrical...