Wind speeds off the coast of Humboldt County in Northern California are some of the strongest in the U.S. The region's steady gusts are so powerful, in fact, that the area was one of three potential offshore wind energy development zones in California included by the federal Bureau of Ocean Energy Management in a public pitch to developers last year.

With around 140,000 residents, Humboldt County lacks one thing offshore wind developers like to see: a big demand for power. But the San Francisco Bay Area is a five-hour drive south along Highway 101. 

If the wind energy zone off the shore of Humboldt County is fully developed, much of the estimated 2,100 megawatts of generating capacity would end up heading south to serve the 8 million residents of the nine-county San Francisco Bay Area. The question is how to get it there.

The existing transmission infrastructure in Humboldt County wasn’t built to export power. An undersea transmission tracking the coastline could very well be the answer.

The entity tasked with providing guidance on transmission and interconnection, as well as other critical issues such as port infrastructure, environmental concerns and economic impacts, is the Schatz Energy Research Center at Humboldt State University. Researchers at the center are conducting three studies to assess offshore wind feasibility in Humboldt Bay. Results are scheduled to be released beginning in March 2020.

Asked in an interview about the region’s limited transmission capacity, Schatz Center director Arne Jacobson said, “Saying that we are somewhat constrained is very generous. I would say we’re connected to the rest of the electrical grid by a capillary.”

Anything beyond a small pilot-scale deployment, he added, “would require some sort of upgrade to the transmission infrastructure or for a fairly significant amount of local storage.”

Piercing the "Redwood Curtain"

Part of what makes Humboldt County so appealing for residents and visitors — the region’s rugged natural beauty — makes overland electricity transmission difficult.

Bisecting the coastal plain — where the cities of Eureka and Arcata sit — and the Central Valley in the interior, are a series of north-south running, densely forested peaks of the Northern Coast Ranges. Any potential upgrades to the existing transmission network must contend with this "Redwood Curtain."

The Schatz Center is studying three scenarios of offshore wind farm deployment: 50-megawatt pilot-scale, 150 megawatts and 2,100 megawatts, which is estimated to be the full build-out of Bureau of Ocean Energy Management's (BOEM) designated 536 km2 “call area” in Humboldt Bay.

In September 2018, Humboldt County’s community-choice aggregator, the Redwood Coast Energy Authority, submitted an unsolicited lease application to BOEM for a 100- to 150-megawatt floating offshore wind farm to be sited in waters more than 20 miles off the coast of Eureka. RCEA’s partners include a consortium of private companies: Principle Power, EDPR Offshore North America and Aker Solutions.

In June, BOEM said it anticipates conducting a California offshore wind lease sale in 2020.

In any scenario beyond a pilot-scale project, the limited transmission capacity in what grid operators call the Humboldt pocket becomes a problem.

The primary grid link serving Eureka is a 115-kilovolt line running east-to-west along Highway 36, designed to carry around 70 megawatts of electricity. “The 115 kV line can move a certain amount of energy, but it’s rather limited," Jacobson said. 

"It wasn’t really designed to necessarily export large volumes of energy,” Jon Stallman, strategic projects manager in the grid innovation and integration unit of Pacific Gas and Electric, said at an energy planning workshop in Arcata conducted by the California Energy Commission in April 2018.

An even more constrained 60 kV transmission line runs along Highway 101 in southern Humboldt County toward the Central Valley.

“To change that system to make it larger is going to be a fairly costly event,” said Stallman.

The average load in Humboldt County is around 110 megawatts, and peak load is between 150 and 170 megawatts. So, even if wind energy development in the area was limited to the project proposed by the Redwood Coast Energy Authority — up to 150 megawatts — exporting at least some power would be necessary.

And a full build-out of Humboldt County’s 2,100-megawatt offshore wind potential would require a significant investment in transmission infrastructure.

The 115 kV line that serves Eureka connects with the larger California grid at a substation in Cottonwood, where it links to the 500 kV, north-south California-Oregon Intertie. If Humboldt Bay offshore wind farms are to export over land, PG&E’s Stallman said grid operators will have to determine if that California-Oregon transmission backbone can carry the additional load.

“We’ve got to take a look at the contracted bandwidth and figure out how we’re going to make room,” said Stallman.

Undersea cable for gigawatt-scale deployment?

No developer has yet proposed building a subsea transmission cable from a substation offshore Humboldt County to the San Francisco region, Jacobson said.

Even so, the Schatz Center is looking into the costs, as well as the technical and environmental challenges. A team in the Seattle office of the coastal engineering firm Mott MacDonald is handling the conceptual design of the undersea cable, while PG&E is tasked with estimating the transmission cost upgrades.

“The challenges would be many, but the challenges are also many with the overland routes,” Jacobson noted.

What is clear is that any offshore wind project in the region larger than pilot-scale — and certainly at full build-out — is contingent on transmission expansion.

“If you were just trying to scale it to the local load, I don’t think you would make it as large as 150 megawatts,” said Jacobson.

“On the other hand,” he went on, “from a profitability perspective, or a cost-viability perspective for investors, I don’t know that it’s that interesting to just build something for this region without leaving a pathway for scaling to something larger.”

“My sense is, and what we’ve heard from developers, is that they’re very happy to do something at [150 megawatts] as a next step in their process, but, ultimately, to become profitable, they need something at a larger scale."

Unlike the Central Coast, California’s other promising offshore wind energy zone, Humboldt County does not face conflicts with active military uses.

“The major constraint we have that’s different from other parts of the state is the transmission one,” said Jacobson. “If there’s not a solution to the transmission issue, there really wouldn’t be a pathway forward at scale here.”


Related report: 'Offshore wind operations and maintenance trends 2019' (May 2019, Wood Mackenzie). Wood Mackenzie is hosting an invite-only analyst briefing on the U.S. offshore wind sector in Boston the morning of Wednesday, October 23. Email [email protected] to express interest in attending.