Transmission network expansion planning: towards enhanced renewable integration

Recent development of renewable distributed generation, strongly affected by the need of reaching objectives established by European Energy and Climate policies, has an important impact on planning and operation of a power system. In this context, TSO has to guarantee major penetration of RES generation ensuring security of supply, efficiency and level of service. In literature, the ability of the electrical system to employ its resources dealing with the changes in load demand and variable generation, is defined as the flexibility of the system. Indexes for evaluation of system's flexibility, defined by European Network Transmission System Operator, are Residual Load and RES ramping. The aim of this paper is to present a methodology to assess the amount of RES generation which must be curtailed to avoid overloads due to existent grid congestions, by extending ENTSO-E indexes. In fact, in the planning framework it is crucial to quantify RES production limits in terms of congestion and system overgeneration. Furthermore, major technical and economic benefits yielded by employing the proposed methodology in planning design of power systems under different scenarios are illustrated.