The addition of significant amount of renewable energy reduces the electrical capacity running at high load factors and increases the value of flexible production: a higher proportion of conventional stations is required to operate only at times when the production from renewables is below average. In those conditions, plants with relatively low capital costs will be favoured over those with low operating costs. First, the optimal generation mix of dispatchable technologies that satisfies at the lowest cost for a given electricity demand, represented by the annual load duration curve, is derived. The same methodology is then applied to the same electricity market after the integration of a given amount of renewable energy.