Offshore wind farms can tap into a bounty of wind that allows them to work twice as productively.
But that efficiency comes at a cost. Like any sea-based technology, wind farms are difficult to build and expensive to maintain, with workers fighting against the same weather that makes the farms work so well.
As a result, terrestrial turbines have been steadily gaining ground compared to turbines built at sea. But that may soon change.
Engineers at GE’s Power Conversion business in Nancy, France, designed an innovative 6-megawatt direct-drive generator — one of the largest ever built — equipped with a permanent magnet rotor.
The design allows them to eliminate the gearbox and reduce the number of moving parts that could potentially break down, and leads to easier maintenance. The team also split the electrical drive train into three independent electrical channels. Even if two go offline, the turbine can still operate on one channel and produce electricity.
Low maintenance and redundancy are hugely important, especially for offshore installations where treacherous waters and high winds can delay a repair trip for days or weeks.
Support vessels cost upwards of $10,000 a day, sourcing spare parts can take time and trained engineers have to be found in a hurry, says Frederic Maenhaut, a renewables executive at GE Power Conversion. “Our direct-drive technology mitigates the main risk to the reliability of a wind turbine — the gearbox,” Maenhaut says. “When it comes to maintenance costs, that makes a big difference. We developed it to be ideal for an offshore setting.”
The generator weighs 150 tons, measures 7.6 meters in diameter and sits hundreds of feet above the waves. It draws rotational energy from a giant GE wind turbine called the Haliade and converts it into electricity. The turbine must be large to move the big magnet. In fact, its 150-meter-diameter rotor covers an area that would fit two double-decker Airbus A380 planes.
The combo’s very first commercial application will be at America’s first offshore wind farm that’s currently being built near Block Island, Rhode Island. Together they will produce enough electricity to power 5,000 American homes.
GE makes the generators in St. Nazaire in France, at the same factory that also produces the Haliades. (GE Reports is visiting the place on Tuesday so make sure to tune in for our Periscopes.) The first GE nacelle with the permanent magnet generator left the plant last week. The plant can make 100 of them per year.
The manufacturing process is in several ways as innovative as the generators themselves. The machines float down the manufacturing line on an air-cushion system that reduces the need for cranes inside the factory. The site also has its own test bench. Workers test every generator before it leaves the factory, rather than shipping it elsewhere for testing.
Maenhaut says the offshore wind market is expected to grow at a rate of 20 percent globally each year through 2020 and he wants to be ready. “Offshore wind is gaining increasing competitiveness in the power mix, and GE is well-positioned to serve this industry,” he says.
