Transmission expansion issues for offshore wind farms integration in Europe

This paper presents an overview of the major issues concerning the expansion of the European transmission system for the connection and for the integration of offshore wind farms. These issues are basically related to: i) the connection solutions for offshore wind farms (infrastructures at sea), ii) the reinforcement of the onshore transmission system for accommodating the power produced by the wind farms, while guaranteeing system security, and iii) the options for facilitating transmission investments (definition of priority projects, funding support schemes, regulatory frameworks). Concerning the first issue, we compare two connection solutions with reference to a 100-MW offshore wind farm: 150 kV alternating current (AC) and high voltage direct current based on voltage sourced converters (VSC-HVDC). An economic assessment takes into account the investment, operation and maintenance costs, and the negative valorization of losses and energy not supplied. As far as the second issue is concerned, we describe the prospects for the development of offshore wind farms and, taking into account the characteristics of the existing European wind and hydro pumped-storage facilities and a possible wind-hydro combination, we discuss the need for system reinforcement. With regard to the third issue, we present the options and instruments which exist and which are under discussion in order to facilitate transmission expansion investments, such as the list of electricity projects of common interest prepared by the European Commission and the regulatory framework of tenders for licensing offshore electricity transmission in the United Kingdom (UK).