Sunday, 31 August 2014
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Competition looks at access to wind farms in stormy weather

Technology to help engineers reach offshore wind farms in stormy conditions is the subject of a design competition by the UK Carbon Trust and eight industrial sponsors.

The ultimate aim is to improve the economics of offshore wind and several potential solutions have now been shortlisted by the Offshore Wind Accelerator programme, which oversees the project.

Each turbine in an offshore wind farm requires an average of four visits a year for routine maintenance, as well as unexpected downtime to replace components.

‘That might not sound like very much, but if you consider a wind farm with 400 turbines out there, then you are busy all year round,’ said Jan Matthiesen, manager of the Accelerator programme.

During downtime, the turbines are in an idle state, where the blades are turned out of the wind and the brakes are applied. ‘It essentially just sits there and waits to be fixed, which is costing you money,’ Matthiesen said.

Maintenance vessels are then launched from shore, that is, provided waves don’t exceed around 1.5m in height. This rarely happens with current farms, which are typically less than 25km offshore, but the next generation could be as far as 300km out with thousands of turbines, presenting greater challenges.

The aim of the project is to come up with a technology that can allow maintenance missions in wave heights of around 3m, which Matthiesen estimates would increase availability of the wind farms for maintenance by four per cent, in turn increasing revenues by £3bn.

He added that there have been various designs put forward, but the chosen solution will most likely incorporate permanent bases or motherships from which daughterships will launch then dock with turbine bases.

‘One particular aspect we looked at was how vessels are behaving when they are not moving — you need to find the right compromise,’ Matthiesen said. ’So they need to be fast enough to move around the wind farm, but they also need to be stable if they are not moving at all.’

Indeed, one shortlisted daughtercraft uses suspension inspired by Paris Dakar-winning rally cars. The prototype boat has six ‘legs’, which are in contact with the surface of the water and move independently to keep the body of the craft still during flight and while docked.

Another shortlisted design uses a giant robotic arm to transfer engineers and equipment from a daughtership to the turbine base.

‘Flexibility is obviously key, so it might be that your mothership has a range of different daughtercrafts, so you can deploy some that are relatively cheap to run, but can only operate if the weather is quite good and then you may have others that are more expensive, with more high technology, but can bring you to the wind turbines in more severe weather,’ Matthiesen said

The shortlisted designs, which are at various stages, will now be developed further with financial help from the Accelerator, which will eventually select technologies for commercialisation.


Readers' comments (6)

  • i cannot believe that they are only now wondering how to get on to a wind turbine platform from the sea in bad weather. Also have they considered provisioning for not being able to get the guys off if the weather deteriorates? Perhaps the powers that be should read up on lighthouse keeping !

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  • May I suggest: "mobilize" the platforms, develop autonomous operation using a Supervisory Control and Data Acquisition System which accounts for platform Velocity Performance Prediction through Computational Fluid Dynamics (VPP/CFD)and path cost/Path yield analysis factors with maintentance performed at a central location in an assembly line manner.

    See video: http://youtu.be/dZCL9ZKdn0M

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  • Will the turbines generate more energy than is used in building, running and scrapping the support vessels?

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  • They tried to tell us that this form of power generation is green - with up to four visits per turbine per year how can that be truely green. From a power generation point of view surely this also drops the over all efficiency of each unit to an unacceptable level.

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  • One way of doing this would be to use a small submarine. There is no swell much below one wave length deep. Create an opening in the base of the tower, seal at TWL with a downward opening hatch. Pressurise to expel the water. The tower would need a broad base like a short legged tuning fork so the sub could pass right through. The tower would have an opening the same shape as the conning tower of the sub.

    "Surface" the sub into the base of the tower

    Make a seal around the edge / side of the conning tower and depressurise the shaft or dispense with pressurisation and simply pump the water out.

    Once shaft is empty and sub is firmly attached to the base, open the hatch and access the tower.

    Opening would have to align with the tide so that sub would only experience tide fore and aft (for stability)

    Sub exterior would have to be free of clutter (snagging)

    Seal design would have avoid jamming as the boat gets more buoyant as the shaft is brought to atmospheric pressure.

    Could navigate along line of cables or guide wire by magnetic induction (expect zero visibility in bad weather)

    Could use mother ship or be shore based.

    Use generator set propulsion as in "Oberon Class" Submarine (but smaller scale) for long rang operation. Use Snorkel for bad weather and run as a submersible

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  • Subs are an idea but there are problems with pile-driving large tubes with holes in them, and it leads to fatigue issues during operation. Even with all the visits, very high turbine operating availability is in the nineties percent these days - do you know what fossil fuel stations availability is !?! if you've even been up close and see the size discrepancy between the 700kW work boat and each single turbine generating nearly 10 times the power, with tens of these turbines being serviced by one vessel, I don't think we need fear that more energy will go into maintenance vessels than is generated !!! They've not just started thinking about the problem... look at SWATHs, Ampelman, FROG, helicopters, hovercrafts for ice and the amazing innovation in the Offshore Wind Accelerator programme - it's a fascinating area of development. The UK could be tomorrow's Energy Sheiks is we wake up and embrace the opportunity !

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