This north-south transfer is already testing the capacity of existing grids to the limit and any expansion of wind capacity will require additional investments in internal transmission. In general, grid reinforcement and extensions benefits all the players of the electricity market, although at different levels. When adding significant amounts of new capacity, it is therefore difficult to allocate those costs among different market participants. In most studies, however, the reinforcement costs have been determined as the additional investments in the transmission grid after the integration of a given amount of renewable energy, in comparison with those required for an “equivalent” system without renewables.