OFFSHORE WIND
NEW POWER GENERATION: NEXT-GEN WTIV SOLUTIONS Closed bus solutions and ring connections are among the power solutions being introduced aboard the latest generation of wind turbine installation vessels, Stevie Knight hears
8 Shimizu’s supersized jackup can carry and install three, 12MW turbines - or seven 8MW units - in a single voyage
Turbine sizes have already reached the 14MW mark, their growth triggering a blossoming of super-sized installation vessel designs with kit to match, capable of taking all the components to site and installing them from foundations to blades. But taking OIM’s BT-220IU and Knud E Hansen’s Atlas C jackup with their respective 2,600t and 3,000t capacity cranes as an example, what are the implications for onboard power? “The cranes are getting taller, the sizes larger,” says John Lindtjorn of ABB, pointing to Shimizu’s latest 142m, 28,000gt jack-up. This can carry and complete the installation of three 12 MW wind turbines in five days using a 2,500t capacity crane with a lifting height of 158m. The WITV’s legs will also extend far enough to enable operations in 65m deep waters. To do all this, it relies on six gensets, four 4.63MW engines, with a pair giving 1.425MW: these power three, 3.8MW main propulsion drives, a couple of 3.2MW tunnel thrusters and a single retractable unit of the same output. Despite the scaling up, “it’s all well within what’s possible”, Lindtjorn adds, but when you add costs and environmental concerns to the mix, things become a little more complicated. “Typically, ships divide up the power plant so that a failure will be limited to one bus section,” he comments: “That makes fault handling fairly simple - every block takes care of itself.” But, he points out, “this has an impact on efficiency, you tend toward low partial loading on each engine, more black smoke and soot, higher running hours and shorter
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maintenance intervals”. Plus there’s no load sharing, so each section has to be sized for the potential peaks. All this impacts cost and environmental performance. Alternatively, “you could have a closed bus, or further, a ring connection”, a strategy chosen by a number of these new generation WITVs, including the Shimizu jackup. This results in higher efficiency, a lower carbon footprint - and potentially smaller engines. With ships of this scale, that can make a big difference. Further, it yields flexibility “as you can configure your power in whatever way you want, to suit a given operation”, says Lindtjorn. A similar argument has also driven the power configuration onboard Jan De Nul’s new 236.8m Les Alizés. The ship has a deadweight of 61,000t and can load foundations weighing up to 5,000t. But it is very different from more traditional jackup designs because installation takes place while floating. Therefore, apart from the four, 3MW Schottel azimuthing thrusters at the stern - giving a maximum speed of 13kn - there are a sizeable pair of 3.25MW retractable units plus two 2.6MW bow thrusters offering DP support. “A floating installation vessel utilising DP mode means that you don’t have to consider payload limitations due to the jacking operation... so you can carry more cargo, further out to site,” says Gunter Servaes of Jan De Nul - so it saves jacking and sailing time. However, he adds “on a DP vessel like Les Alizés; everything needs to work together continuously, so the harsher the conditions, the more power you need to minimise movement”.
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