Keeping the hope for more offshore power afloat with wind turbines

The evolution of floating wind turbines mirrors almost exactly that of offshore oil exploration and production structures. Norwegian oil company Statoil’s decision to build the first floating wind farm represents a carbon risk hedge in an area in which it can deploy its considerable offshore expertise. If costs can be reduced, floating wind farms would hugely expand the exploitable wind resource. Ross McCracken, managing editor of Platts' Energy Economist, explains.

Wind energy is developing a new avenue of expansion, one which should hugely increase the technically, and possibly economically, exploitable wind resource. Wind is going further offshore.

The problem to date has been that further offshore means deeper water and bigger foundations, raising costs, but the industry needs to move in precisely the opposite direction and reduce costs. However, the oil and gas industry has already confronted and resolved this dilemma, moved from fixed platforms to semi-submersibles and then, particularly in the Gulf of Mexico, to spars.

These are huge structures, which use a central, floating, ballasted cylinder to provide stability. The Gulf of Mexico now hosts some 52 permanent deepwater structures in water depths of between 300 to 2,500 meters.

This technology is being applied to offshore wind. Norwegian oil company Statoil is to build a 30 MW floating wind farm off Scotland, using a spar structure, while the WindFloat consortium plans a 25 MW farm off Portugal using a semi-submersible design. Both are based on successful demonstration projects, which used ‘off the shelf’ turbines of 2.3 MW and 2.0 MW respectively. The larger planned farms will use 5-6 MW turbines and will be the first floating wind farms in the world. Completion is expected in 2017/18.

Scaling up turbine size reduces costs, but floating wind turbines have additional potential for cost reduction. Production and installation of the substructure of a conventional offshore wind turbine represents up to 20% of the total cost. Floating wind turbines can be fully constructed onshore and in sheltered conditions, which should facilitate factory line production and assembly. Towing out to site fully assembled reduces offshore operations and allows for the turbine to be brought back to shore for maintenance if required.

Given the expectation that wind turbine size will continue rising to at least 10 MW, offshore wind has considerable cost reduction potential on top of the gains already made. Moreover, floating turbine technology would allow wind farms to be sited in water depths of between 50 and 226 meters, compared to the current limitation of grounded substructures of 40-50 meters. So – potentially at least – lower costs and more sites, suggesting wind energy has a lot more to give.

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