Cost Analysis of 15MW Platforms for Horizontal and Vertical Axis Turbines in the West Coast U.S.A.

Steffen Shelley, VP Renewable Energy, VL Offshore LLC
The floating foundations installed to date are designed to be continuously fabricated at one location as a single piece with complex braces. This conventional fabrication approach works reasonably well for smaller size turbine foundations but does not scale well for larger turbine foundations with limited infra structures. The US offshore floating wind industry is thus seeking technologies in order to overcome infrastructure limits and to reduce the LCOE for floating foundations for 15MW and larger. Infrastructure for constructing and assembling very large floating wind units is limited on the US West Coast.

One solution is to undertake significant capital expenditures to upgrade existing infrastructure, which is unlikely. Another solution is to build large foundation hulls in the Gulf of Mexico or in Asia, then to transport them to the West Coast for the tower integration. This solution adds significant transport costs and schedule or execution risks to the wind farm projects.

An alternative and promising solution is to implement a modular floating fabrication to utilize existing infrastructure in the West Coast, while also reducing total fabrication and assembly. VL Offshore (VLO) has developed a scalable, modular floating foundation hull for large turbines. In this study, the cost of the modular semi-type foundations with 15 MW HAWT (NREL/IEA) and 15 MW VAWT (UT Dallas) are compared.

A site located off the California coast is selected. Through coupled dynamic simulations, each platform responses for the operating, extreme and survival conditions are computed and compared with the design criteria against ABS and API, for compliance check. The costs of the platforms are estimated for a 200 MW wind farm, considering all the cost parameters of the platform hull and mooring and installation, excluding the turbine costs. In addition, inter-array power cables, export power cables excluding the static cable and one floating substation are considered. It is confirmed that there is a significant cost reduction against the conventional platform with no modular hull capability.