Controlling the cost of maintaining turbine availability up to 300km offshore will be crucial to operator returns from the UK’s £75bn Round 3 offshore wind projects.

By Toby Procter, UK correspondent

Offshore wind farm operators will be up against a host of new O&M challenges following the roll out of Round 3. What are the key issues and strategies being considered in the UK Carbon Trust’s £30m Offshore Wind Accelerator (OWA) research, which aims to cut overall offshore generation costs by 10 percent?

Colin Morgan, director of offshore wind at consulting engineers Garrad Hassan, expects the availability, or machine reliability, of next-generation offshore turbines to come out in the low 90s compared to the average 97-98 percent reliability achieved in onshore turbines.

Why the deficit? In part, this will be due to more frequent occurrence of turbine operation at full power.

But for the main part, it will be due to the huge challenge of repair access. When operating offshore, time is money, particularly when a crane vessel costing up to £50,000 per day is required. Operators will need bigger, better turbines, and optimum access systems. 

Morgan expects maintenance strategies to be determined by the size of arrays and their distance from port. Up to 60 turbines 10 miles offshore may deploy shore-based teams (typically two engineers for every 20-30 turbines) using fast boats, while the planned Dogger Bank array may keep a permanent offshore-based maintenance team of around 20, fully occupied.

The Carbon Trust’s senior technology acceleration manager, Benjamin Sykes, senior technology acceleration manager, expects to see offshore O&M teams housed either on fixed platforms alongside electricity substations, or on mother ships which would shepherd the smaller vessels needed to access turbines.

This is because transferring to turbines by boat from either will remain difficult or impossible in storm conditions that coincide with weather-induced turbine failures.  The North Sea offshore oil and gas operators have already demonstrated the risks of helicopter access to offshore platforms, and as Sykes points out, a chopper cannot be landed on a turbine nacelle made inaccessible by its own rotor.

Rapid response not enough

Anders Søe-Jensen, president of Vestas Offshore says his business has turned away from rapid response O&M teams.

He explains: “An on-site team ensures highly committed people that hold a sense of ownership in relation to their particular site. If you have to drag people away from one site to another when a problem occurs you are always in a situation where you have to prioritize one site over another – and this can never be the best solution for our customers as it can result in a conflict of interest.”

Sykes believes that the five OWA research co-funders (DONG Energy, Airtricity, RWE Innogy, Scottish Power Renewables and Statoil) have provided a solid understanding of what Round 3 offshore arrays will involve in terms of reliability factors, maintenance frequency and repair job times.

Garrad Hassan has used such data, in conjunction with maximum wave height data, to build an O&M model to define what access systems may best combine efficiency with safety. Three of a long-list of 15 access systems studied have been shortlisted for development work.

The J P Kenny Offshore Renewables Group has also been working with the Carbon Trust on the access, logistics and transport stream of the OWA.

J P Kenny has separately researched hydraulic wave and tidal power-to-shore transmission, which for wind arrays, could minimize offshore maintenance by locating generators on land.

Maintenance teams’ productivity will clearly be crucial, given offshore cost and access challenges. Vestas Offshore’s Anders Søe-Jensen says it’s essentially down to planning.

“Before our technicians sail out to a turbine they have beforehand analyzed the situation and have prepared a thorough plan to ensure that, once out there, they carry out all maintenance and repair relevant for that particular turbine. We also try to bundle turbine visits,” he explains.

Effective condition monitoring (CMS), supervisory control and data acquisition (SCADA) and asset integrity management (AIM) systems are required for optimum inspection and preventive maintenance scheduling.

“The Vestas Control Center gives us a complete overview of the status and performance of all wind turbines at a site. We know in advance exactly what we need to be aware of and fix,” says Søe-Jensen.

The area where the least experience is available is where the cost of failure will be highest. In this case, it is materials fatigue that will affect the biggest turbines -  to a largely unknown degree. J P Kenny Offshore Group has experience of replacing a gearbox bearing in situ on one of the 85m turbines on the Beatrice wind farm 25km off the East coast of Scotland. 

While turbine makers sell warranted equipment with maintenance contracts, Garrad Hassan’s Colin Morgan expects some of the UK Round 3 consortia to want to get actively involved alongside suppliers. Meanwhile, he expects turbine manufacturers will be busy designing-out as many breakdowns as possible by adding in redundancy in electrical components.

Windfall for Northeast economy

With around £75 billion committed, Round 3 offshore wind investment will resemble the North Sea oil and gas boom of the 1970s. Around 75% of this will be invested off the North East coast, where the oil and gas sector has already spawned the makings of a home-grown turbine manufacturing and support industry.

The regional development agency One North East’s energy and engineering manager Ray Thompson expects offshore maintenance crews to be drawn from the same regional workforce involved in deployment:  “Any equipment that needs to be brought ashore for repairs will stay as close to the sea as possible.”

Until the results of the OWA research are made public, it is anyone’s guess as to which will be the preferred O&M strategies for maximising next-generation offshore turbine availability. And only around 2011-12, when the first large-scale demonstration projects have deployed O&M strategies for at least a year, will the strongest of these strategies emerge.  

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