Floating wind turbines, you might recall, are proposed as a way to access the superior wind available in deep ocean waters. But a Cambridge University engineer believes that closer to shore there might be stunningly simple new approaches to turbine construction that could improve the return on offshore wind power investment.
Jim Platts from the university’s Institute for Manufacturing, a veteran of the offshore wind industry, says the harvesting ratio of offshore turbines – that is, the amount of the energy produced vs. the energy used to make the turbine – could be vastly increased if manufacturers used guy wires to hold turbines in place while also building with composite materials instead of conventional steel.
To hear Platts tell it, making this change is something of a no-brainer.
“The development of the wind turbine industry, and the way in which it works with the civil engineers who make the heavy supporting towers and foundations, which are not visible out at sea once the turbines are installed, mean that we have ignored something which is almost embarrassingly obvious in our race to meet the targets set for renewable energy production,” Platts said in a statement.
You might be surprised at how much material it takes to do the standard offshore wind turbine installation. The towers look nice and slender rising out of the sea, but like an iceberg, there’s a lot more going on under the surface. “What you don’t see are the far heavier supporting structures below the surface that they slot into,” said Platts. Those foundations use up to four times more steel and concrete then onshore turbines.
To close that gap, Platts recommends guy wires – aka, stay cables – anchored to the sea bed. (He doesn’t say if they would attach to the tower above or below the water’s surface.) According to Platts, early studies show that guy wires would allow for slimmer towers and “substantially less weighty” foundations.
It isn’t clear if Platts is proposing compliant towers, which are flexible and absorb much of force of the wind and the sea and are not uncommon in deep-sea oil and gas drilling and exploration. This sort of design for offshore wind turbines was looked at closely in a 2009 European Commission-funded study [PDF], and one of the six concepts presented included the use of guy wires, as pictured below. In any case, he says that using the guy wires and, in turn, much less steel and concrete, the turbines could boost their harvesting ratio from 15:1 to 25:1.
Then there’s the matter of the composite materials, which Platts says are less energy intensive to make than steel, less prone to corrosion and stand up better to fatigue. “Using these new materials could increase the harvesting ratio still further to 32:1 and extend the lifetime of a turbine installation from the present 20 years to up to 60 years,” Platts said.
The Cambridge engineer pointed to Mervento, a Finnish company, that is using guy wires in new turbine designs. On their website, we were only able to find such uses for onshore turbines, but the rationale is as Platts describes – “enabling a relatively small foundation,” the company says.