IN DEPTH: How Vestas' 7MW giant became an 8MW monster

Eighteen months after Vestas unveiled its 7MW V164 wind turbine as “the new ruler at sea”, the Danish manufacturing giant has raised the bar again — by upping the unit’s capacity to 8MW.

The two versions of the turbine are to all appearances the same. At the heart of the design, the drivetrain remains a three-stage medium-speed geared system that steps up the ten to 12 revolutions per minute (rpm) of the rotor to 400rpm inside the liquid-cooled permanent-magnet generator.

But fine-tuning, according to chief technology officer Anders Vedel, has led to a higher-output version of the machine “that will offer lower cost of energy without sacrificing the reliability or structural integrity” of the original design. Plans remain on track to have the first model up and turning by 2014.

“There have been no structural changes, no changes to the layout of the turbine — the turbine was in the beginning laid out for 8MW — but by further scrutinising the energy reserves in the turbine it became clear we could take it to the 8MW level rather than to 7MW first and then later to 8MW,” Vedel tells Recharge.

Vestas’ fingertip search for areas in the design that could be upgraded led to discovering aspects of the gearbox and generator “where validation could ensure that the turbine can produce all that it is capable of producing”.

“[Since the launch of the V164], we have been communicating that it is 7MW until we were absolutely certain of its top output,” adds Vedel, who took up his post in February.

The V164 is purpose-built for 25-years’ service in hostile offshore environments and extreme temperatures, with a rotor swept area of more than 21,000 square metres.

The 8MW turbine’s slimline 80-metre blades derive their modelling from that of the 54.6-metre “Risø B” design for the V112-3.0MW. However, the 35-tonne blade will depart from Vestas’ box-shell-and-spar design, employing “structural shell” technology that allows the wind loads to be borne by the outer shell of the blade itself.

“We have the moulding tool in place and are working with the layout to double-check our processes, so that before we start laying out the first blade, we will have conducted quite a number of test runs, both with respect to laying out of materials as well as the curing processes and so on,” says Vedel.

The V164-8.0MW converter and transformer will be housed in the tower base to ease service access and boost reliability by not exposing them to the higher vibration levels and variable temperatures inside the nacelle.

Vedel acknowledges that there have been snags in the development timeline for the V164 since its launch in London in March 2011, but he points out that the company has gone to great lengths to make up for lost time by pressing ahead with the ordering and incorporating of long-lead-time items, including the hub, gearbox and generator, so as not fall further behind schedule.

“We have been working hard both within Vestas and with our sub-suppliers to make sure that these components will be ready when we need them,” he states. “Because these long-lead items, if they are not en route, could prevent us from getting the [prototype] up in good time.”

Plans to scale down “pure” research and development (R&D) in favour of product development, as announced by the company last week, will free up “a substantial engineering resource” to be devoted to the V164 and other models.

“We are scaling down, it is true, but we are also narrowing the focus on the turbines that will give us actual delivery of the technologies that will be game-changers,” says Vedel.

The V164 prototype’s hub has been cast at the group’s R&D centre on the Isle of Wight, southern England, and is now ready for testing. The mould for the machine’s blades is waiting for first fabrication and load testing later this year.

The turbine’s complete drive-train is expected to be installed on a purpose-built test bench at the company’s Aarhus facility in the first quarter of 2013.

“All required parts are in delivery,” says Vedel. “The test bench will finally be commissioned in January and then we can begin testing the drivetrain in earnest.

“Our capability to do in-house testing of the V164 gives us a competitive advantage. It improves the reliability of the turbine and thereby the business-case certainty for our customers.”

The V164’s 24-metre-long, 12-metre-wide, 7.5-metre-high nacelle and transformer will together weigh 290 tonnes, while the rotor hub and blades come in at 210 tonnes.

Although foreseen in the first instance to be mated with jacket foundations offshore, Vedel reckons the turbine would be an ideal fit for future floating concepts.

“[The V164] could be a good turbine for that. Whether it will prove to be a viable solution will ultimately depend on the sites chosen by our customers — if they are deep-water sites then the floating concept is an obvious one.”

Installation of the flagship onshore V164-8.0MW turbine at the Danish national wind testing centre at Østerild is slated for 2014.