GE originally started looking at offshore in the 2000s, and in 2003 the company supplied 7 of its 3.6 MW wind turbines for the Irish offshore wind farm Arklow Bank. The wind turbine design is largely a scale-up of GE’s 1.5 MW turbine, Product Manager Offshore at GE, Vincent Schellings, tells Renewable Energy Focus.

GE’s offshore focus was relatively short-lived, however. “We recognised that the offshore wind market was relatively small, so we withdrew from the offshore sector. But in the meantime we still owned that wind farm and we kept gathering information, data and operation experience.

“Then in 2009, it became clear that the offshore market was really starting to kick off, and therefore we were looking at opportunities to get back into the sector.”

Schellings adds: “With the experience that we gained on Arklow, there was one element that became clear to us, and that was that in our view, for offshore wind farms, we need to use direct drive technology.”

GE looked at various options, including in-house R&D, but decided in the end to buy ScanWind in 2009. ScanWind already had a 3.5 MW direct drive wind turbine with a 90 m rotor. A fleet of 14 units have been operational at Hundhammerfjellet wind farm in Nord-Trøndelag county, Norway, since 2005 in a high wind area (~9.2 m/s average wind speed), on a cliff, near the sea. Schellings says the conditions are almost like offshore, with difficult servicing and high turbulence.

He explains that GE has made use of the ScanWind design for its GE 4.1-113, but upped its ratings: “We took the generator rating from 3.5 MW to 4.1 MW, we took the rotor diameter up from 90 m to 113 m, and with that, the annual energy production goes up 43% – with virtually the same machine.”

GE also built on the design of its 2.5 MW machine to for example mitigate the load increases with the larger turbine size with, amongst other things, single blade pitch control.

Asked what the difference is between GE’s direct drive wind turbine, and other recently announced offshore wind turbines with similar technology, Schellings explains: “The difference with our turbine compare to the competition is: We have the only built for purpose offshore direct drive turbine. […] And with this design we have five years of operating experience. Through operating experience you learn a lot about the reliability of the design, you get the opportunity to improve it. So we got a couple of years head start on the competition for offshore direct drive applications.

“The other element of our turbine that is unique is that basically all the equipment is based inside the nacelle, which enables us to do full commissioning and quality checks in the shop and then after installation at sea, we basically only need to drop down the cable and plug it in – and theoretically, we can push the start button.”

GE announced last July it is planning an onshore installation of its direct drive wind turbines in 2011. The offshore wind turbine will be erected in Gothenburg Harbour in Sweden in cooperation with Gothenburg Energy. “That version will mainly be used to validate the performance characteristics. […] And then next year, the goal is to put a unit in the water to demonstrate our installation procedures and commissioning procedures, as well as that the services concept works the way we plan it to work,” Schellings says.

Permanent magnet drives

Permanent magnet drives are said to offer many benefits offshore over their geared counterparts in terms of maintenance requirements, but it is also known that the materials used for permanent magnet drives can be expensive.

“They are more expensive, but they also lead to higher efficiency,” Schellings explains. “I used to be involved in the development of our 2.5 MW unit for onshore applications, and there we found that a generator with permanent magnets actually provides 2-3% more annual energy production than a more conventional generator.”

Despite the praise for direct drive, Schellings does not believe we have come to the end of geared solutions. “At an offshore application direct drive leads to the lowest cost of electricity, but for onshore applications we still believe in gear designs. That’s why we’re so successful with the 1.5 and the 2.5 MW. It works, but it’s a different environment.”

The foundations

Looking to foundations, Schellings explains that GE will use whatever foundation is the most cost competitive, and at the moment, that is monopile. He does not exclude other foundations, but says that in the long term, GE will look into jacket foundations, gravity-based foundations, etc. “In the first couple of years the projects that will be built, will be built on the sites where you can install the units most effectively, which definitely is shallow water where you can use monopiles.”

When it comes to access systems offshore, Schellings says GE does not have a preference – it is up to the customer, and what makes economic sense for each project. “Obviously vessels are available, but some projects also use helicopters. It is all about economics. A helicopter is more expensive, but you get quicker to the site, so you have less down-time, which improves the economics – it’s always a trade-off you need to make.”

Markets for the 4.1 MW

Asked what markets GE will promote its 4.1 MW offshore wind turbine to, Schellings says both the UK’s Round 3 and the expected French tender are of interest. “We go where our customers go, but obviously, the UK today is where most of the action is.” As GE has its offshore headquarters in Germany, Germany is also an attractive market.

Although the US has not yet got offshore wind farms in operation, GE believes North America to have potential. In May 2010, GE announced a partnership with Lake Erie Energy Development Corporation (LEEDCo) to install five direct drive offshore turbines at a demonstration site in Lake Eerie. However, for the US to become an attractive market for offshore wind, Schellings says politicians must back development; “US policy still has to firm up a little bit to really get started offshore, but no doubt that we will see offshore win din the US as well. But our main focus for now is obviously Europe. This is where most of the action is happening.”

Cost reduction through innovation

Looking towards the future, Schellings says: “We’re always looking for new technology, we are a technology company, but our focus is: What technology can we use to lower the cost of electricity? And the move to direct drive for offshore was because we think that if you look at the entire lifecycle of the wind farm, you will achieve lower cost of electricity offshore with a direct drive turbine.” Schelling ads that there might be better solutions out there that will become cost effective once built in larger quantities.

For example, “we always look at opportunities to make the rotor larger. It might sound very simple to make it a little larger, but larger also means higher loads and therefore also higher cost. So how do we do it in a way that will reduce the cost of electricity? That’s always the challenge.”

Although technology may change with time, Schellings says GE’s approach to design stays the same: “We take a proven platform and then we build upon it.” For wind the opportunities for development usually lie around the rotor and the generator rating.

“We’ve done that with the 1.5 MW for 15 years now. The original 1.5 only had a 65 m rotor, today we have a 1.6 MW with a 100 m rotor – there were about 10 steps in between, and that’s how we do product development – in incremental steps. The beauty of that is that every time you have a new piece of technology available you infuse it and make another incremental step, but with that you retain the track record of the existing fleet – you only change one thing at a time, and the other thing is, you also maintain your cost position.”

Asked about the possibility of developing 20 MW wind turbines in the future, alluded to at EWEA 2011, Schellings says that it could be possible in theory, but that it would not be cost effective. GE is not considering developing such machines in the foreseeable future, but as Schellings points out: “If you look back 20 years, a couple of the first turbines that were installed were very large – 4.5 MW type turbines – but at that time they did not have the technology to do it cost competitively. They only built one and that was it.”