Cost Model for Floating Multi-Megawatt Vertical Axis Wind Turbines

Abstract

In an effort to achieve economic sustainability, the major challenge for offshore wind remains to bring down costs by approximately 35 % before 2020. With wind farm sites going into deeper waters, further from shore, with more difficult bottom conditions and rougher wave climate, costs are rising faster than the improvements in the technology are able to drive them down. Despite these obstacles, wind farms further offshore offer better wind resource, less socio-economic restrictions and diminished environmental impacts. To satiate this need, floating wind turbines provide a feasible promise. In the wake of current Horizontal Axis Wind Turbine (Hawt) floating projects such as HyWind, IDEOL etc, the perceived positive impact of the floating system, especially for larger scale machines, is reduced due to large overturning moments and difficult accessibility of the \moving" nacelle. A possible solution to these obstacles is presented by the DeepWind project which focuses on implementing a Floating Offshore Vertical Axis Wind Turbine (Fo-Vawt) on a spar structure. In this report, the economic feasibility of a Fo-Vawt concept in far offshore wind farm is assessed - from current to multi-megawatt rated power. The possible benefits of a Fo-Vawt are translated into cost indicators for the main aspects of an offshore wind farm project. The difference in turbine capex, perceived reductions in balance of plant costs and the impact on opex, is modelled into an engineering framework to determine the Levelised Cost of Energy. Considering mass and swept area as the base factors, the mass of the baseline DeepWind turbine design [66] is approximated and broken down into material and manufacturing costs with adjustments for inflation and other financial variables over the lifetime of the wind farm. Using ECN's omce package, a detailed operations and maintenance (O&M) strategy is devised and implemented with respect to Vawt systems and a floating wind farm. The grid infrastructure, installation and project development costs are estimated using TU Delft's Offshore Wind Farm Design Emulator tool developed by Zaaijer [75]. All these components are combined to deduce the cost of energy for the DeepWind and the turbine capital costs for similar turbine designs. To study the design space of the cost model, a sensitivity study of the main presumptions was done along with an evaluation of LCoE impact from rotor, floater and generator design. Using geometric up-scaling methods, the baseline Fo-Vawt design was sized for higher rated power capacities and corresponding loads simulated using HAWC2. Considering a 245 MW wind farm, a workspace was created to assess where the greatest potential in cost reductions exist and provide impact trigger's for future research . It was seen that the turbine capital costs for a Vawt are not significantly higher than for a comparable state-of-the-art 5MW Hawt. The reliability of a Vawt is better and subsequently the wind farm has a higher availability, assuming the same technology maturity level as a present day Hawt. Although, possible higher fixed capital costs originate for the specialised supply chain to maintain floating turbines and the DeepWind subsystems. This on average pushes the annual opex beyond e120/kW. The capex/kW extends between e2520 to e2780/ kW for the 5 to 15 MW Fo-Vawt's respectively, leading to a Levelised Cost of Energy frome113.56 to 117.1 per MWh.