In Europe, offshore wind farms have traditionally been built in the shallow watersof the North Sea and the Mediterranean. Until recently, it was too expensiveand difficult to build offshore wind farms in deeper waters. However, due tothe ground breaking work of various technologists and engineers, a new solution has been found for placing offshore wind turbines in deeper waters such as the coast of California and Norway. As a result, in December, the US government took the first steps in leasing deep-water areas of the coast of California for offshore wind development. This means that we could see the first deep-waterwind turbines in operation supplying the Californian power sector from 2024 onwards.
In the shallow waters of the American east coast, it is possible to pile a single foundation tube directly into the seabed on which will stand the tower,turbine, and blades. However, off the West Coast, the seabed is typically 300 feet or more in depth. As a result, the wind turbine kit and tower must float on a platform tethered to the sea bottom.
For offshore wind turbine developers, there are added problems including the desire of locals for such developments not to spoil their views. Although, they seem happy to live with thousands of oil derricks, utility poles and cables etcetera spoiling their urban vistas. As a result, for Californian offshore windpower developers, such projects need to be at least 15 to 20 miles offshore, well hidden from view on the coast.
A matter of tethering
For engineers, finding secure solutions for tethering deep-water floating windfarms is proving especially challenging, especially in extreme weather whentyphoons can reach category five or more. One of the leading engineering companies involved in finding secure solutions for offshore wind farms is HR Wallingford based near Oxford. It has created toolkit designers can use toconfigure the optimal platform tethering system for any location. The tool kit utilises computational fluid dynamics based on Proteus open source software and multi-body dynamics using the Chrono open source solver.
A senior engineer at HR Wallingford Dr. AggelosDimakopoulos says, “We have put a special focus on the fully dynamic simulation of mooring cables, as they can significantly affect station‑keeping and the overall response of the device which in turn affects its energyextraction efficiency.” The team at HR Wallingford is using a computational fluid dynamics model in order to reduce costs in design optimisation, by performing full-scale simulations under realistic sea conditions, before performing laboratory tests, which may be subject to practical limitations.This is vital as it helps provides a further opportunity to cut the levelised cost of producing electricity offshore.
Already, off the coast of Norway and Scotland, developers have been using floating offshore wind farms to generate electricity for the grid. With California, it should be possible for existing grid-connected coastal substations to be directly connected by sub-sea cables to offshore wind projects. For investors and policymakers, development of offshore wind projects is seen as a good way to replace many of the existing gas power plants, which are scheduled to be shut down by 2045, when California aims to achieve its goal of being 100%renewable. In addition, it is scheduled that the state’s last remaining 2.2 GW nuclear power plant at Diablo Canyon will be decommissioned by 2025.
Three Coastal Areas Identified
At present, there are three potential areas for offshore wind development in Californian waters. The first is in northern California of Humboldt County; in addition, there are two sites in the Morro Bay area of the Central Coast nearHearst Castle and Diablo Canyon. “California has a very good offshore wind,”says Walt Musial, a principal engineer, and manager of offshore wind efforts at the National Renewable Energy Laboratory.
Already, a state-run utility known as Redwood Coast, which serves some 60,000 customers in a mostly rural area of Humboldt County, has announced plans to invest some $500 million in an offshore deep-water wind farm. “That level of generation would be a significant chunk of our energy load,” says Matthew Marshall, the utilities executive director. “Offshore wind is really the big untapped resource.”
In terms of cost, there is very little difference between a floating project and a fixed bottom project, since they use many of the same components. In fact, some elements make floating wind farm projects cheaper than fixed bottom schemes.
Thereare at present three major companies that have the technological experience available to build large-scale offshore floating wind farms. Three companies with offshore wind experience are expected to bid on the leases when they become available in about 18 months — Equinor, which used to be Statoil, the Norwegian state owned energy company, Trident Winds, and Magellan Wind, which is working with Copenhagen Infrastructure Partners. Trident winds envision a 100-turbine project 33 miles west of Morro Bay.
The challenge of planning approval
There are several steps that need to be made be for the final go-ahead fordevelopment of the proposed offshore sites for wind projects. These include a series of reviews and federal and state level, including the project promoters gaining approval from the California Coastal Commission for impact on federal and state waters, the California State Lands Commission, and the California Department of Fish and Wildlife because of concern about protected species.
For the state of California, offshore wind is a matter of catch up, since they have to catch up with offshore wind developers and experts in Europe. One thing is for certain, it is no longer a prospect of if there will be an offshore wind business in California, but one of figuring out the best solution for making it work.