Abstract
Offshore wind energy development in the United States has to date consisted of fixed-bottom wind turbines in the Atlantic Ocean off the east coast. Planned areas for future offshore wind development include deeper waters offshore Maine, Oregon, and California. In these areas where water depths drop off much more steeply, projects cannot use fixed-bottom technology. The use of floating technologies with buoyant substructures in deeper waters will result in a different physical footprint that could impact offshore wind plant design, installation, and operations.
The Bureau of Ocean Energy Management (BOEM) is the lead federal agency for planning and leasing areas for offshore wind on the United States Outer Continental Shelf. Once an area is leased, the company then develops and submits to BOEM a Construction and Operations Plan (COP). This plan contains the proposed design specifications that all permitting agencies use to evaluate a project. A project design envelope (PDE) approach is a project plan that adheres to a reasonable range of project design parameters. BOEM gives offshore renewable energy lessees the option to use a PDE approach when submitting a COP and issued draft guidance to this effect in 2018 (BOEM 2018). There are benefits to allowing lessees to describe a reasonable range of project designs in a COP given project complexity, the unpredictability of the environment in which it will be constructed, and/or the rapid pace of technological development within the industry. Many leaseholders off the U.S. east coast have utilized the PDE approach in their COPs. No COPs exist for floating offshore wind projects in United States federal waters.
A representative project design envelope (RPDE) provides estimates of the scale and number of components in a floating offshore wind facility when there is a need to describe impacts but there is not yet a PDE to evaluate. This report describes RPDE recommendations developed by the National Renewable Energy Laboratory (NREL) for floating offshore wind energy projects. In the development of these recommendations, we considered industry feedback from offshore wind farm developers in the California lease areas and a practical range of technology options that may be deployed, accounting for major physical constraints and technical readiness.
Section 2 of this report presents the RPDE, and Sections 3 and 4 present four scenarios that illustrate some of the differences between technologies that could be used offshore California, as well as descriptions of the typical installation processes that are expected to be used for floating offshore wind farms. These two sections are intended to provide greater depth and context for the information presented in the RPDE, but do not represent a comprehensive analysis of the design space and possible installation methods. This report does not represent real or proposed projects. It is an attempt to capture a realistic range of technical specifications and layouts of floating wind facilities given the water depths, wind characteristics, and distance from shore of the lease areas offshore California.