Power Transmission Systems for Offshore Wind Farms

Résumé du livre

Several studies claim that wind power will play a major role in the energy supply of the European Union, forecasting 70 GW of new installed capacity in the next five years. Given the accelerated growth that offshore wind power is experiencing, many challenges are to be addressed in the next few years and substantial improvements are to be expected. Offshore wind farms (OWF) are expected to increase in rated power and in distance from shore, thus increasing the relevance of the transmission system. Therefore, a detailed technical-economic analysis is necessary to estimate which is the optimal transmission system to transmit the power generated at the OWF. This thesis presents a technical-economic analysis of power transmission systems for OWF. The aim of this work is to determine the most suitable power transmission technology for a given set of OWF characteristics. Costs and losses of different proposed technologies are investigated: high-voltage alternating current (HVAC), high-voltage direct current (HVDC) based on voltage-source converters (VSC), and low-frequency alternating current (LFAC). For the technical part of the analysis, the strengths and weaknesses of each technology are exposed, as well as the role of the main components investigated. Regarding the economic side of the thesis, the costs of the major components of each transmission system are associated to cost functions, and their losses modelled. Availability of the components is also considered, as well as the variability of the self-made cost functions. The self-made cost functions, being contributions of this work, are provided for public use. The costs of the whole transmission system including losses are obtained as a function of a range of variables (transmission length, rated power, voltage level, etc.). Additionally, the employed cost functions and loss calculations are summarized in a spreadsheet, which is openly available upon request. Besides giving the cost functions, the technical-economic analysis is applied to a set of case studies to draw a comparison between a range of proposed transmission systems. The obtained results indicate that the break-even point between HVAC and HVDC is to be found in the 50-100 km range, approaching 50 km in the case of large OWF (e.g. 1000 MW). Additionally, the studied cases also reveal that LFAC could result the most suitable option in the 50-70 km range.