The pilot installation of the SWT-6.0s, which will stand in 15 metres of water next to developer Dong Energy’s Gunfleet Sands wind farm, 8.5km off the southeast coast of England, will see construction work start next month on the landfall section of the project, where the turbines’ export cable will be linked to the grid.
Offshore activity for Gunfleet is expected to kick off in July, with power flowing from the demonstration site by the end of the year down a dedicated line supplied by JDR Cable Systems.
Dong has yet to choose the construction and installation vessels to be used on the project.
“We see the Gunfleet Sands 3 project as a great opportunity to advance a technology that we believe will bring the cost of energy down — both the capital and operations spends,” says Dong Energy UK operations director Benj Sykes.
“Moving from the 3.6MW machines [installed at the 172MW Gunfleet Sands 1 and 2] to the 6.0s is a very large step towards getting more out of the balance of plant in the coming rounds of offshore developments off Britain.”
This is the first offshore outing for Siemens’ 6MW concept, its first turbine “dedicated” to hostile marine environments. All external surfaces and systems feature “offshore-grade” corrosion protection, and the climate-controlled nacelle is a self-contained medium-voltage power plant, designed to be pre-commissioned onshore for plug-in at site, with a built-in workshop, crane and coffee machine.
“We have a significant testing programme ahead,” says Siemens head of offshore Michael Hannibal, “including a full battery of measurement tests along with certain reliability and power-curve tests that we have agreed with Dong.
“We only ever take proven technologies offshore — from our 2.0 model to, now, our 6.0. The testing at Gunfleet Sands is really vital to us to get our next generation of machines ready.”
The exhaustive testing programme is “open-ended”, notes Sykes. “This is about building confidence over time.”
A prototype of the SWT-6.0 has been turning onshore at Høvsøre, Denmark, for almost a year, with “surprisingly no surprises”, says Hannibal.
The SWT-6.0 is Siemens’ third direct-drive machine. By swapping out the main shaft, gearbox and high-speed generator for a low-speed, synchronous permanent-magnet generator, it claims two thirds of the conventional drivetrain assembly is removed — meaning the turbine has 50% fewer parts “than a comparable geared machine” and is lighter, with a top-head mass of less than 350 tonnes.
Siemens and Dong have gone to great lengths to rule out variables in testing the new machine. The first SWT-6.0 at Gunfleet Sands will be kitted out with a 120-metre rotor — the standard set of blades used on Siemens’ 3.6MW offshore machine — that will be mounted on a conventional steel tower with monopile foundation.
The 6MW concept was first designed with a 154-metre rotor, which would have a swept area of 18,600 square metres for maximum energy capture in locations “from inland waters with moderate wind resources to the most exposed offshore site”.
Wind speeds at Gunfleet Sands average 9.5 metres per second.
But Hannibal says: “We know everything about the 120-metre rotor — its aerodynamics, its wind loads — so when you match it up with the 6MW nacelle the results we get will tell us more because we know what part of the overall machine we are testing.
“Once the new nacelle’s performance is known, then we can fit it with the larger rotor. We are taking it step by step, controlling as many variables as we can.”
Sykes adds: “Likewise, the choice of monopile. We know how they behave offshore, we know the dynamics that come with this sort of foundation. To have put the 6.0 on a new type of foundation would have introduced unknowns that could have muddied the water.”
Plans are fast taking shape to erect a pair of Siemens’ 6MW direct-drive wind turbines at the first of four sites marked out by the UK Crown Estate for demonstration testing of the next generation of offshore machines.
The SWT-6.0 will be marketed with the 120-metre-rotor option for locations where air-traffic regulations restrict turbine tip-heights to 150 metres.
Both the 120-metre and 154-metre rotors use blades manufactured using Siemens’ IntegralBlade technology, which casts each unit in a single process rather than gluing it together from spars and shells. This method produces lightweight, high-strength blades that do not have the issue of joins that could crack in high winds or prove a weak point in a lightning strike.
Siemens has re-engineered the aerodynamic and structural design of the blades for the 154-metre rotor using its Quantum Blade technology, with a particular focus on a “lift-enhancing” tip and a root section reworked with “flatback” profiles to stanch root leakage and boost lift.
The SWT-6.0 model being installed by Gunfleet Sands has been dubbed “turbina sapiens” by the company for its advanced diagnostics system, which helps the turbine “think for itself” to manage operating loads and feed back real-time performance data and servicing needs of all componentry based on “lifetime use”.
Dong is testing the Siemens turbines at Gunfleet Sands with an eye on its “small” UK Round 3 sites — the 1GW Njord and 2GW Heron projects.
The Gunfleet Sands 3 demonstration has been “fast-tracked”, with its project timeline going from consent to completed construction offshore in under a year. Serial production of the SWT-6.0 is planned for 2014.
