Equinor considers driving huge pilings into LI seabed for wind turbines 

When New York State in 2018 awarded a multibillion dollar contract to Norwegian energy giant Equinor to build wind turbines off the Long Island coast, one critical element of the award was its planned use of giant concrete foundations.

That choice would lead to hundreds of mostly Albany-area jobs and provide “tremendous environmental advantage, minimizing risks to fish and wildlife,” according to the state that year.

But Equinor has yet to fully commit to using those “gravity-base structures” for the project, or for another larger wind farm to be constructed adjacent to it. Its recently filed construction and operation plan provides a detailed review of an alternative option: using giant monopiles that are driven into the seabed from a pile-driving barge.

In the same report, Equinor noted that a gravity-base structure “under environmental forces is more sensitive to weak horizontal layers across the foundation footings.” And it says that the concrete foundations have already been “removed from consideration” for use in an offshore substation that’s part of the project because of “design challenges.”

Asked this week whether the concrete foundations, which act much like heavy backyard umbrella stands to keep the turbines upright in stressful offshore conditions, were still in the cards, an Equinor spokeswoman hedged.

“We aim to use the best foundations for our project possible – from an environmental, operational, construction and long-term commercial standpoint,” spokeswoman Lauren Shane said in a statement. She noted the construction plan “contemplates both gravity-base structure (GBS) and monopile foundation types. We continue to assess the viability of both types, along with a number of other significant elements, as we move toward finalizing the project design.”

Using pile-driven monopiles has one significant advantage over gravity-based concrete foundations: cost. That could have some bearing after Equinor’s Norwegian parent recently reported that its U.S. oil and gas operations sustained losses of $21.5 billion between 2007 and 2019. But it would also mean the 600 to 800 promised jobs making the giant concrete structures in the Albany region could be significantly reduced or eliminated.

The New York State Energy Research and Development Authority, which formally awarded the contract to Equinor over some 18 other projects, in a statement last week also left open the prospect that multiple options were available for Equinor to complete the project.

“NYSERDA expects Equinor will make the best choices to execute a Construction and Operations Plan that is the most efficient, cost-effective and safe for marine life,” NYSERDA marketing vice president Kate Muller said in written responses.

She added that “It has always been understood that specific foundation positions might not be feasible for use of gravity-base foundations, depending on the geophysical, geotechnical findings and other technical seafloor and technology characteristics, which could result in alternatives being considered.”

And Muller noted that Equinor’s “pre-engineering work is ongoing and their current public permitting approach with the Bureau of Ocean Energy Management reflects a design envelope framework that encapsulates a range of diverse alternatives in consideration of such factors.”

Were Equinor to move to all pile-driven turbine structures, Muller said it would not reduce other financial commitments made by the company. “Equinor has made contractual economic commitments to the state for its offshore wind projects, including obligations for the delivery of approximately $792 million in in-state spending and economic development for the Empire Wind 1 project,” she said.

Asked if the state would consider the impact of pile driving on whales and other sea life, Muller said the agency is “committed to working with the offshore industry, industry experts, and stakeholders to ensure New York’s offshore wind projects are cost-effectively and responsibly built for the benefit of New Yorkers and the environment, while utilizing strong mitigation planning throughout.”

Equinor had been considerably more certain about its foundation plans at conferences and presentations since winning the award in a ceremony with former Gov. Andrew M. Cuomo and former U.S. Vice President Al Gore in 2018. At an offshore wind-power conference at the SUNY Maritime College in September, 2019, gravity-base foundations were the only option discussed.

Under the headline, “Let’s power New York’s future together,” the presentation listed only the concrete foundations “manufactured in the Capital Region,” and presented artists’ conceptional drawings of ships towing them down the Hudson. The presentation promised “thousands of jobs,” in bold, while creating a “manufacturing hub for concrete foundations.”

In its recent construction and operation plan filed with the federal Bureau of Ocean Energy Management, Equinor has excluded gravity-base concrete foundations for use with an offshore substation that sits among the turbines, noting the “operational challenges” associated with boat landing and “accommodation of the crew transfer vessel.”

As for the turbines themselves, the report notes that a concrete foundation “requires the upper soil layers to have the strength to sustain the heavier load. The surface may require improvements to support distributing such a load and stabilizing installation.” That could mean installing a separate gravel pad under each concrete foundation, dredging “loose sand to be replaced by rock fill or the use of skirts,” according to the report.

Pile-driving a monopile for the turbines avoids those issues, the report noted, and Empire has already studied the “drivability” of the seabed. It found that driving a 246-foot monopile into the ground would require as many as 3,506 “blows” of a pile-driving hammer, and as few as 626.

The document concluded that monopiles and piled “jackets,” which are also driven into the ground, are “in general robust structures, where bearing capacity and structure integrity may be designed safely with adjusted pile penetration depth, pile diameter and pile wall thickness.”

Survey work is continuing on the two primary options, monopile and concrete base, as well as pile-jacket foundations, Equinor said.

In a 2019 study of gravity-base foundations in the Journal of Marine Science and Engineering, the structures were found to have “good behavior” when used in the offshore oil and gas industry, with “high-load-bearing capacity.”

The downsides?

“It has not had great acceptance in the wind industry up to now,” it needs to be placed in soil with “specific geotechnical properties,” with soil preparation needed; and it has a large footprint on the seabed. Monopiles, by comparison, boast “simplicity of structure,” as well as lower cost, the authors found.