By Rikki Stancich

In the UK’s bid to install 33GW of offshore wind power by 2020, some 6,000 turbines will need to be installed in UK waters within the decade. With the average size of wind farm expected to rise from 30-100 turbines to as many as 2,500 per site by the end of the decade. At a distance of between 65km – 285km from the coast, the operating environment of these wind farms will be very different from today’s offshore wind farms, which are less than 25km from shore. 

The increased distance from shore automatically implies a rougher sea state and higher safety risks for engineers carrying out routine maintenance. With Round 3 construction dates fast approaching, offshore service providers must quickly develop innovative solutions to transfer personnel and equipment safely in increasingly harsh conditions.

The UK’s Carbon Trust, via its Offshore Wind Accelerator programme, is encouraging companies to tackle the challenge head-on by offering several million in funding for the best solutions for transfer systems, vessel design and launch and recovery systems. The objective is to dramatically improve the availability of turbines and the safety of people during the transfer to turbines.

Wind Energy Update's Rikki Stancich speaks to Phil de Villiers, Offshore Wind Accelerator manager about the challenges faced by offshore service providers and possible solutions to resolve these issues.

Wind Energy Update: Far shore wind farms imply more complicated logistics and costs. What main cost drivers have been identified by the Carbon Trust?

Phil de Villiers: The Offshore Wind Accelerator programme includes eight developers who have options to develop 30 GW in UK waters. Their view is that the largest Round 3 site, Dogger Bank will be larger than the other nine projects.

We are focusing on four key areas, including the foundations and structures (which account for up to 45% of capital expenditure), on electrical systems (how to minimize losses and build redundancy into layouts; wake effects (maximizing yield through layout); and access systems through operations and maintenance. We are not looking at the turbines themselves, as we believe the original equipment manufacturers are best positioned to deliver cost benefits. 

Wind Energy Update: The Carbon Trust estimates that by 2020, the average offshore wind farm will comprise 2,500 turbines. This will require new thinking for O&M strategies and access systems in order to service this number of turbines.  What are the limitations of existing solutions and what are the potential future solutions?

Phil de Villiers: Today’s wind farms are less than 20 kilometres from shore. Often they are 100MW developments with 30 turbines. So we are talking about small, near-shore developments with kind met ocean conditions, which require relatively simple access systems.

Currently the most common access method is for the vessel to go from port to turbine, where the crew clips onto a rope and steps onto the turbine. The risk is that the boat is not secured to the turbine, so if there was a large wave, the boat could lose contact with the turbine. Also, the ladders could be slippery. Another possible hazard is that if the engineer is close to the boat and the boat moves up, it could injure the engineer.

Today these risks are manageable, however, the next-generation wind farms could be as far as 65 kilometres from shore. The far edge of Dogger bank is almost 300 kilometres from shore. In these instances, the Met Ocean conditions are more severe and the average wave height is much higher. Crew transfer therefore becomes more risky and the challenge of getting to the turbine is greater.

As such, we need a new O&M strategy. We need a manned platform or mother ship on which a crew is positioned on a permanent basis, with turbine access vessels.

With regard to transfer systems, we need to move away from friction-based systems to avoid operations being restricted by the sea state.

Another challenge is not so much the monopile, but the jackets, which will require different transport systems. A boat using friction to fix against a monopile has a larger area to fix against than a jacket structure – and you can’t approach the jacket from all sides.

One way to resolve this is to have sea bridges – a gangway that locks into place on the turbine, with hydraulics that could heat-compensate the bridge. The engineer could then walk across the sea-bridge, which could have a handrail or fence. So the crew wouldn’t be stepping form the vessel using a ladder.

To complement this we are looking for two other technologies. A likely future strategy is to have a mother ship with smaller vessels launched from the mother ship for operations and maintenance.

Wind Energy Update: In terms of O&M costs and turbine availability, what kind of cost savings could be achieved via such solutions?

Phil de Villiers: The capacity of the launch and recovery system is dictated by the kind of vessel being used. The bigger the vessel, the more stable and easier it is to transfer, but larger vessels cost more to run, they are slower, and they are more difficult to life onto the mother ship. On the flip side, the smaller vessel compromises on transfer capacity.

More than likely, we’ll need to build new service vessels.

Using today’s solutions, you would be limited in accessing the turbines. The weather window for servicing far shore turbines is increased substantially - over 4% for a power generation increase and 3% improvement for Round 3 sites.

By increasing the availability by 3-4% the ecomomic advantage is the same yield for less assets; another way of looking at it, is the increase in revenues in terms of the hours that turbines generate power, i.e. an increase of 3-4%.

Wind Energy Update: What investment is required (into vessels, transfer systems and launch and recovery systems) to realise the vision of mega far-shore wind farms?

Phil de Villiers: We estimate over the next ten years a global send of around £2 billion on commissioning and building mother ships, service vessels and transfer ships. Around 50% of that will be spent in UK waters.

Wind Energy Update: Is there a risk that legislation could hold back technological advances in transfer and access systems?

Phil de Villiers:  As the regulation evolves, it should consider improvements in access systems. This will probably be the case if regulation lags behind technological developments – if regulations are tailored to out-of-date equipment.

This is why we need the certification companies and industry groups to continue to inform the regulators.

The Offshore Wind Accelerator (OWA), is a collaborative R&D project between the Carbon Trust and eight leading international offshore wind farm developers. Its goal is to develop technologies to drive down the cost of offshore wind, focusing on four research areas: Foundations, Wake Effects, Electrical Systems, and Access. The closing date for entries is November 26.

To respond to this article, please write to the editor: Rikki Stancich