Schatz Energy Research Center
Transmission line runs through rural Humboldt County

Report: Offshore wind transmission scenarios for Northern California and Southern Oregon

We recently released a new report that evaluates potential scenarios for electric grid transmission development to support floating offshore wind along the northern coast of California and the southern coast of Oregon. The scenarios include onshore and offshore (undersea) transmission systems, with interconnections ranging from 7.2 to 25.8 gigawatts of generation capacity. The study encompasses multiple possible wind farm sites between Coos Bay, Oregon and Cape Mendocino, California, including the two currently awarded lease areas located 20 miles off California’s Humboldt Bay, and two Draft Wind Energy Areas near Brookings and Coos Bay, Oregon.

Because the existing transmission infrastructure in these rural, coastal areas is very limited, major investments will be required to support offshore wind development. This report estimates that transmission infrastructure costs could range from $7.5 billion for a 7.2 gigawatt wind farm to as much as $41.3 billion for a 25.8 gigawatt buildout. For the 7.2 gigawatt scenario, annual system-wide benefits are estimated to be roughly $1.2 billion, when compared to a base case without offshore wind generation. These savings include both production cost savings and greenhouse gas emissions savings; the latter is valued at $72 per metric ton of avoided emissions, based on the EPA’s projected social cost of carbon.

The report examines combinations of onshore and offshore transmission solutions, utilizing both high-voltage alternating current (HVAC) and high-voltage direct current (HVDC). Estimates also include the costs to deliver wind power to nearby coastal communities. The analysis indicates that coastal communities near wind farms could be connected to the new transmission infrastructure, thereby increasing the reliability and available capacity of electricity in those areas, for only 0.4% to 2.4% of the overall cost of the transmission upgrades.

This study also includes a preliminary assessment of anticipated permitting challenges related to environmental impacts, land use conflicts, and undersea cable routing. The findings indicate significant variations in permitting difficulty, ranging from low to very high among the various possible routes.

Because the Pacific offshore wind buildout will take decades to accomplish, the report emphasizes that infrastructure investment decisions made in the early phases must be informed by expected long-term strategies—both to minimize cost and impact, and so that developments do not become stranded. Proactive, regional transmission planning is critical. Likewise, technologies installed today must be designed to adapt to future solutions.

We recommend next steps including taking a more detailed look at near-term transmission needs for the first phase of offshore wind development; a detailed analysis of transmission routes, land ownership, and rights-of-way; and an assessment of the potential to couple battery energy storage with offshore wind.

This study was funded by the California Energy Commission and the Office of Local Defense Community Cooperation of the U.S. Department of Defense, and developed in close collaboration with the Oregon Department of Energy. Technical project partners included the National Renewable Energy Laboratory, Quanta Technology, H. T. Harvey & Associates, Mott MacDonald, and Conaway Geomatics.

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