Winding up the gigawatts

Offshore wind is blowing past the barriers for renewable energy–the technical barriers, anyway.

The U.S. aims to gather 30 gigawatts of power from offshore wind fields by 2030, one enormously ambitious goal. On the technology side, the biggest challenge is bringing the power ashore and integrating it into our not terribly robust existing power grids, while our demands for electricity soar.

But for the wind turbine technology itself, the U.S. can tap into the rapid advances in largescale wind farms globally. That’s what we heard from Danielle Merfeld, chief technology officer for GE Renewable Energy, at a forum on offshore wind sponsored by the National Academy of Engineering’s Gulf Research Program.

Largescale, yes. In fact, today’s turbines are “the largest moving machines humanity has ever built,” Merfeld remarked. “A 15-megawatt offshore wind turbine is on the scale of the Eiffel Tower.”

Manufacturing these monsters is obviously more than tricky. GE’s latest turbines have 107-meter blades, as long as a football field with endzones. “We have to think in a completely different way to be able to efficiently manufacture these blades,” she said. The nacelles, which draw energy off those spinning blades, are correspondingly huge (top right).

Installing the gargantuan machines at sea will be no easy task. There are very few of the required jackup boats (below left) and none under the U.S. flag. Offshore field developers will need many jackups to get anywhere close to the 30GW goal. “And by the end of the decade, some of those vessels will be obsolete because we’ll move to even bigger systems,” Merfeld commented.

Additionally, offshore wind fields more than 30 miles from shore shore will want to run DC power cables. That calls for an AC-to-DC conversion platforms, perhaps as tall as a 15-story building and as wide as a football field, built onshore and towed out to sea. “These are, again, big engineering challenges,” Merfeld said.

Turbines also typically require five or more maintenance visits a year, she said. GE’s new Jules Verne (below right) is a high-tech “service operation vehicle” designed to hang out on a wind farm for days to handle everything from lubricating moving parts to replacing blades.

These giant structures bring significant environmental worries above and below the sea. Early experience with the five GE turbines installed off Block Island suggest that turbines do act as artificial reefs. “There was a tremendous amount of increase in sea life activity, so the fishermen were happier than they thought they were going to be,” Merfeld claimed.

The humongous blades remain big threats to migrating birds, but operators are learning ways to reduce the killing. “Some of it is in the siting,” she said. “You don’t put a wind farm in the middle of a migratory lane for birds, or you turn [the turbines] off during certain migratory periods where you need a week, or even days or hours of the night or day when you expect [birds] to go through.” New mitigation approaches may help. A study last year found that painting one blade black can reduce bird strikes by more than 70%, she added.

All these engineering and environmental demands will be topped by offshore wind’s tough economic, regulatory and political barriers. But in the U.S., as Barbara Kates-Garnick of Tufts University remarked at the forum, “offshore wind is critical to a successful energy transition.”

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