By Sam Phipps in Edinburgh

Over the next ten years and beyond, Round 3 projects built in deeper waters, further from shore, face installation, and operation and maintenance challenges in harsh North Sea conditions. Unless engineers can access turbines safely and with relative ease in order to limit downtime, the viability of offshore these wind projects could be seriously compromised.

Fully aware of what is at stake, developers and operators have bent to the task of devising novel solutions. Many of these have been prompted by a Carbon Trust competition that has drawn entries from the oil and gas, shipbuilding, marine engineering and aerospace sectors, as well as several universities.

“We’ve seen some very credible and innovative ideas submitted and the breadth of interest has been staggering,” said Phil de Villiers, head of the offshore wind accelerator (OWA) scheme at Carbon Trust. “We’ve even had an entry from Nepal, a land-locked country not well-known for its maritime engineering industry.”

Innovation pays

More than 300 organisations have entered from the UK, 120 from North America and 110 from continental Europe, including 35 from Norway. The deadline was November 26.

Successful applicants will win up to £100,000 per concept for design and development; the chance to work with eight leading offshore wind developers with licences to develop 30GW of offshore capacity in UK waters (representing 60% of today’s licensed UK capacity) and potentially several million pounds to take the concepts to full-scale demonstration.

There are likely to be several winners but Carbon Trust has not yet specified how many.

OWA is a collaboration of eight leading energy companies – DONG Energy, E.ON, Mainstream Renewable Power, RWE Innogy, ScottishPower Renewables, SSE Renewables, Statkraft and Statoil – whose aim is to drive down offshore wind energy costs by 10%.

Safety first

Carbon Trust predicts the global market for access solutions for deeper water offshore wind environments will be more than £2bn by 2020, with the UK alone accounting for up to 50%.

The key is to enable safe transfer of personnel and equipment to a turbine in three metre waves. This will allow wider maintenance opportunities, with increased turbine operating hours and thus better economics.

Turbines typically generate electricity for 90% of the time and the competition aims to raise this by at least four percentage points, which equates to saving £3bn in lost revenue and 1.3 million tonnes of CO2 emissions each year.

Among the entrants is UK marine engineering firm Houlder, which has teamed up with naval architects BMT Nigel Gee to develop a turbine access system that minimises vessel motions and provides a stable gangway to the tower via a motion-compensated ramp.

The design submitted is a mark two version of a system already developed by Houlder and BMT that is due to be delivered to field developers in spring 2011 with a patent pending.

“Wave height is the main safety concern with turbine access,” said Mike Carter, marketing manager of Houlder Ltd. “The higher the wave height the more dangerous the process. At the moment most access systems can operate up to 1.5m significant wave height. TAS mark one achieves 2.0m. Mark two could reach up to 3.0m,” i.e. it can handle rougher seas.

“Although it provides sophisticated motion control, you don’t need a new vessel design or to invest in significant modifications such as dynamic positioning for existing vessels. You can take an 18m to 25m workboat and retrofit the TAS relatively easily.”

Houlder's Renewable Energy business has also contributed to Carbon Trust OWA entries for the infield launch and recovery of workboats and new mothership and floating accommodation concepts. This reflects the company's belief that far offshore operations will suit fully integrated access solutions most.

“Our purpose marketing TAS is primarily safety but the system impacts positively on the bottom line,” Carter said. “We have calculated that an uplift in the significant wave height at which maintenance is possible could improve turbine availability from 80% to 90%. This means a potential saving of £245,000 per 5MW turbine, so if you take the proposed 9GW Dogger Bank field this equates to possible extra revenue of £441m a year.”

Bridging the gap

Earlier this year, Aberdeen-based Sea Energy PLC signed an exclusivity agreement with Ampelmann to incorporate the Ampelmann self-stabilising access system, which absorbs the movement of the ship and keeps the platform and bridge hovering in the air, motionless relative to a fixed object such as a turbine tower.

“The advantage of this system is that it does not require fixtures or fittings to the individual turbine structure, which can be very costly to install and maintain in large wind farm arrays,” said Robert Trahan, CEO, Marine Division of Sea Energy PLC.

Meanwhile, the OWA consortium is also building a new docking system for maintenance boats. Led by Statoil, the Sea Bridge will provide a stable 15-metre bridge between turbine and vessel. “It works using cables that hang off the turbine,” said De Villiers. You grab the cables and then the bridge is activated and moves along the cables to the boat, providing a secure fixed link.”

Others have been focusing on reducing the need for maintenance.

The novel vertical axis (NOVA) turbine, a 120 metre Y-shaped structure, is under development. All major maintenance would be carried out at the base of the tower. NOVA has won a £20m grant from the Energy Technologies Institute (ETI), and the goal is to have a working 1GW turbine installed by 2020, with a smaller prototype running within less than five years.

Operators including GE have switched to gearless technology, which they say will improve reliability and cut downtime.

Such progress will ensure developers and operators are not out of their depth as wind farms are constructed at increasinlgy greater distances from shore.

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Image credit: The Ampelmann turbine access system undergoes its first operational test. Image courtesy of Ampelmann.