JUNE/JULY 2013 | £5.25 - Wind Energy Network

OFFSHORE ACCOMMODATIONOFFSHORE ACCOMMODATIONNearshore &farshore windfarmsa whole differentballgameApart from a few exceptions,most of the offshore wind farmsdeveloped in Europe so far havebeen located near to shore enablingroutine maintenance activities to besupported from onshore supportbases using either small craft orhelicopters for personnel access.UK Round 3With the planned developments nowmoving further out into deeper watersfar from shore, the routine maintenancelogistics become more complex and thisespecially the case for UK Round 3 windfarms which are all located beyond the 12mile territorial limit at distances of up to100 miles.ConsiderationsThere are many different influencingfactors to consider when planning themaintenance logistics of these far fromshore wind farms. In deeper waters, thefoundations will be different to the typicalmonopole or gravity based types thathave dominated the shallow near to shoredevelopments and most likely these willbe jackets or even floating structures.Boarding jacket foundations requires asimilar type of access device currentlyused for monopiles. The round trip timesfor these vessels means that only close toshore developments can be served fromshore based vessels.Additional specialistmaintenanceFarshore wind farms also bring withthem additional specialist maintenancerequirements. Due to their distance andlengths of cables, there will be a largenumber of Transformer Substationsand HVDC Convertor Platforms eachwith its own requirement to cater for thepermanent maintenance personnel.UK regulatory regimeIn UK waters, the regulatory approach tooffshore maintenance activities will mostlikely follow a similar framework used forthe oil & gas industry as laid down andmonitored by the UK’s Health and SafetyExecutive (HSE).All offshore oil and gas activities aremanaged the use of a CombinedOperations Safety Case as requiredunder the Offshore Installations (SafetyCase) Regulations 2005 (SCR05). SafetyCases are risk based with the Duty Holder(Operator) being required to set outPerformance Standards which then formsthe basis of how all activities are thenimplemented. A similar approach is alsoused in the Norwegian sector.It is expected that the HSE will require thesame Safety Case risk based approach tothe operations and maintenance activitiesrequired by the far from shore wind farmdevelopments.Oil and gas experienceOil and gas platforms vary but areessentially either fixed steel jackets orgravity base structures or floating unitssuch as FPSOs, FPUs or Drilling Rigs.Routine access to all of these is byhelicopter.Over the years the use of boat or cranebasket transfer of personnel has becomevirtually outlawed due to the inherent risksand the accidents that have occurred.Through the Safety Case risk studies, thehelicopter travel to and from the platformshas been shown to be the largestcontributing factor to fatalities offshoreso these helicopter movements areminimised by careful planning of rotas androutines of the personnel working offshore.With the large number of farshore turbinesplanned, the maintenance routines cannotbe supported directly by small craftoperating directly from onshore due tothe strict safety requirements of Maritimeand Coastguard Agency (MCA). Similarlyfor safety reasons, routine access byhelicopter is neither practical nor desirable.Lessons learnedLessons can be learned from the oil andgas industry, unfortunately it is seen as anexpensive industry and has been largelyignored by some sectors of the offshorewind industry leading to costly mistakessuch as the grouted connections used onsome of the monopile foundations.Whereas mistakes like these have beenvery expensive to fix, when it comes topersonnel safety, short cuts are not anoption.Possible ways forwardThere are a variety of proposed schemesbeing developed for safely housing andferrying personnel to, from and within theoffshore wind farms. Mother and daughtercraft are proposed similar to the navy’sapproach to deploying their amphibiouslanding craft. The Seawind concept belowis an example of such an arrangement.Permanently moored vessels similar to aflat barge are another. The concept shownbelow developed by SEATEL would bedesigned to be moored indefinitely up to70 miles offshore, secured using a singlepoint mooring system and a fixed anchorspread specifically designed for eachlocation.Oil and Gas experience however wouldsuggest that spread moored vesselsare not the way to go for the UK waters.Spread moored Floating ProductionUnits (FPUs) are only used in very benignwaters such as offshore West Africa. Forthe UKCS, weather vaning FPSOs arenow deployed throughout although thereare two examples of spread mooredcylindrical hulled FPSOs but these are notflat barge based designs.Flotels have been used in the oil and gasindustry for many years and these arenormally based on a semi-submersible hullmoored to the seabed similar to a drillingrig.Operational experience of FPSOs showsthat helicopter movements are regularlyhampered by the motions of the vessels ineven moderate sea conditions, thereforebarge based concepts would most likelynot provide the operational conditionsrequired for all year round maintenanceactivities.Fixed offshore accommodationplatformsThe most obvious and well proven solutionis a permanent accommodation modulelocated within the wind farm. Separateaccommodation platforms do provide allof the requirements for personnel safetyand comfort.Accommodation areas can also beincorporated into the very large HVDCplatforms being proposed providedthat safe barriers can be incorporatedpersonnel protection.A concept for a HVDC platformDONG Energy is experienced in oil andgas and are now well established in theoffshore wind industry. For their Horns RevII wind farm located 19 miles offshore inthe Danish sector, DONG have installeda permanent Accommodation platformlocated alongside the TransformerSubstation.This is the first permanent accommodationmodule to be installed in an offshore windfarm and sets the scene for others tofollow. The maintenance crew are housedinside a standard 24 man accommodationmodule is designed and built to offshoreoil and gas standards. The crew fly to andfrom onshore by helicopter allowing safemaintenance conducted 365 days a year.104www.windenergynetwork.co.ukwww.windenergynetwork.co.uk 105