Page 21: of Offshore Engineer Magazine (Sep/Oct 2022)

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ASSET LIFE EXTENSION

However, as well as building new wind farms to last longer, operators are looking at how to squeeze more life out of their existing farms as they near the end of their 20-year life. Scroby, for example, was recently the subject of a DNV study to assess how much longer RWE could continue to squeeze energy out of it, beyond its 20-year expected life.

Through an assessment, looking at the design assump- tions, such as soil stiffness, which impacts the frequency of the structure and fatigue cycles, and then actual data, actual frequency, to calculate loading from wind and waves, etc., as well as corrosion survey data, condition re- ports and SCADA data, an additional fve years of life was added to the farm. That’s 25% extra time to keeping earning cash.

DNV makes these assessments using its Bladed soft- ware, a simulation tool used to optimize turbines at every phase of its design, in this case using a time history analy- sis, with an aero-elastic model developed by DNV.

It’s worthwhile work, says Traylor. It’s harder to predict conditions offshore, compared with onshore, so designs can be conservative, which means they can have more life in them, he says. As-built conditions might be better than assumed; the operating conditions might be differ- ent. At Scroby, for example, the turbines had been well designed, the ground conditions were generally better than assumed, and it was found that updated ambient turbulence was found to be lower than the original de- sign calculations.

WHAT ABOUT REPOWERING

It can also a more realistic option than repowering, he suggests. But asset owners are still mulling their options, says Traylor. “We were recently asked to look at what the best options are for an asset; sweat it until the operating costs of enhanced maintenance exceed the cost of keep- ing it running or take a refurbishment strategy for the blades and certain other parts to extend the life time. It’s life was 20 years,” says Huw Traylor, Principal Consul- all about balancing the levelized cost of energy (LCOE).” tant and Business Manager, Offshore Technology De- Repowering does have challenges, he says. For one, to- partment, DNV. “More recently (for new wind farms), day’s turbines are much, much larger than they were 20 that’s changed to 25 and we’re seeing 30 years as a stan- years ago. dard now,” he says, refecting licensing regimes, such as Indeed, repowering hasn’t been tackled to any signif- the UK’s Round 4, which now offer 60-year licenses, up icant degree yet in offshore wind. Five 550 kW Wind- from 50, allowing for two full project life cycles (based on World turbines, installed in 1998, off the coast of the is- 30-year life span). land of Gotland, Sweden were re-commissioned in 2018,

SEPTEMBER/OCTOBER 2022 OFFSHORE ENGINEER 21