Technical and Economical Evaluation of DC High-Temperature Superconductor Solutions for the Grid Connection of Offshore Wind Parks

The connection system of offshore wind parks with the onshore power grid can have a crucial impact on the overall energy yield. The possible (ac and dc) connection systems for offshore wind parks are investigated in detail and compared both in terms of cost and losses. Both conventional copper (Cu) cables and high-temperature superconductor (HTS) cables are considered in the case of dc systems. An offshore wind park with a 360-MW peak power capacity in a 50-km distance from the shore is considered as within this case study. The comparison between the connection systems is carried out in terms of overall energy loss in a full year. The economical comparison is also discussed in detail. It is shown that a hybrid (HTS and Cu) medium-voltage dc connection system with a two-stage dc collector grid followed by an HTS high-voltage dc transmission at ±150 kV offers reduced losses and is cost competitive with respect to ac connection systems based on today's quotation of HTS material. In the near future, as soon as the foreseen reduction in the cost of HTS material is achieved, a full-HTS dc connection system can become the most cost-attractive solution.