IN DEPTH: Wind to calm the storm

Mark Jacobson says about 78,000 turbines would be needed in waters along the US East Coast to mitigate hurricane damage

Mark Jacobson says about 78,000 turbines would be needed in waters along the US East Coast to mitigate hurricane damage

Mega-storms that cause billions of dollars’ damage as they tear into the US East Coast and Gulf of Mexico every year could be foiled by vast arrays of offshore wind farms.

A study headed by engineering professor Mark Jacobson of California’s Stanford University used advanced weather modelling to work out that erecting 300GW of turbines would do the trick.

Strategically placed in the waters along the eastern seaboard (battered in 2012 by Hurricane Sandy) and the Gulf coast (hit by Isaac in 2012 and devastated by Katrina in 2005) these huge developments could slow down winds by 40 metres per second (more than 145km/h) and curb storm surge by 80%.

This would have made a huge difference with Hurricane Katrina, which hit landfall at 225km/h, and would lessen the impact of the weaker 120-180km/h hurricanes that are more common on the East Coast, reducing them to the force of a tropical depression or storm.

“Turbines extract energy from the wind and so reduce its speed, but whether they would do so efficiently I couldn’t know until I ran some simulations,” says Jacobson, who had been working on separate pieces of research in the areas of hurricane modelling and global wind potential before he thought to combine the two for the current study.

“So we looked at three of the most famous hurricanes and modelled them against the theoretical impact of having turbines offshore in certain areas. We found you not only reduce the wind speed, you also dissipate the central pressure of hurricane, because when you reduce the wind speed, you reduce the size of the waves, which give hurricanes the friction to turn.”

In one computer simulation, Hurricane Sandy was let loose on offshore wind farms lining most of the East Coast; not only were winds greatly diminished, but up to 26.5 terawatt hours of power flowed on to the grid in the process.

tech_quote.jpgBut why wouldn’t the turbines shut down or be wrecked in such extreme winds? First, ideally, they should be “typhoon class” machines. And Jacobson calculates that the sheer number of turbines would spread the loads sufficiently that they would not be damaged.

The on-paper economics — which crunched data from REpower’s geared 5MW model and Enercon’s direct-drive 7.5MW E-126 — are eye-catching. Factoring in hurricane damage avoidance, reduced pollution, and health and climate costs, the net cost of offshore wind comes down to $0.04-0.085 per kWh, says Jacobson, well below the average $0.10/kWh for new fossil-fuel generation.

Even comparing life-cycle costs with sea walls — which soak up storm surge but do nothing to slow winds — his numbers look promising. Building a $210bn array of turbines arranged along 32km of coastline upwind of New York City would cost ten times more than a sea wall. But as well as curbing storm surge by 34%, it would repay the investment several times over during its lifetime with electricity output, while stopping mega-storms taking a bite out of the Big Apple.

By Jacobson’s reckoning, wind farms in the water off New Orleans would have absorbed 79% of the storm surge while muffling winds by up to 35% during Katrina.

“You pay the turbines off just by selling the electricity, and there are social benefits,” he says. “The additional hurricane protection benefit, risk reduction, in a way comes free. You just need enough wind turbines. Which would be around 78,000.”

Here’s the rub. For a country with a dozen offshore wind farms in the planning stage but no steel in the water — and a supply chain only beginning to take shape — the idea of installing that many machines has its doubters, ranging from those who regard it as “borderline feasible” to others who call it “an insane number”.

Jacobson sees this as either “denial or ignorance”, pointing to the growth of renewables’ contribution to energy supply. “The whole of the world’s power infrastructure will eventually be converted to carry renewable energy, starting with wind and solar,” he adds.

“Look at the growth of onshore wind — or solar, the largest new source of electricity in the US last year. Things are changing so rapidly.

“There is no economic or technological reason that this cannot be done. I anticipate by 2050 we will have hundreds of thousands of offshore wind turbines. Costs are coming down and the winds are so reliable offshore that intermittency is not the issue it is onshore.”

There is no question that these are highly ambitious targets. Building so many machines would require a “wartime” manufacturing campaign, and the logistics of installation are mind-boggling, considering that the fastest installation vessels afloat, Fred Olsen’s Brave Tern and Bold Tern, set a record last month with the placement of eight turbines in one week — just over 400 a year working non-stop.

But, argues Jacobson, “It is only a question of will. We went from virtually nothing to building 330,000 aircraft in five years during World War Two. It is only a matter of deciding what can be done if we choose to do it.”

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