Response to government consultation

Professor emeritus Finn Gunnar Nielsen from the Bergen Offshore Wind Centre (BOW) is one of those who has worked on the consultation response. A key point in the response is the uncertainty of the cost estimates.

"To assume that costs for both bottom-fixed and floating turbines increase proportionally with water depth, is a crude and unrealistic assumption" says Finn Gunnar Nielsen.

He elaborates that for bottom-fixed turbines, the weight — and thus the cost — of the tower or monopile increases (at least) quadratically with water depth, because the strength and stiffness must be sufficient. Whereas the costs of other parts are determined by frequencies of the rotor and therefore independent of water depth. For floating turbines, the situation is different: the cost of the floater can be assumed to be independent of depth. Mooring in shallow areas is challenging, as the system tends to become too stiff. There is therefore little reason to believe that the cost of the mooring system is lower in the shallowest areas than in deeper ones. The areas that are assessed as most technically and economically suitable for bottom-fixed wind turbines are at a challenging depth, both for bottom-fixed and floating turbines (e.g. 65 meters for area called "Southwest B"). 

"If the depth dependency in the cost model is incorrect, the ranking of the areas could change significantly", says Finn Gunnar Nielsen.

It is unclear where the cost figures come from

The consultation describes calculations performed by AFRY, which uses references databases from their own projects, external data, and country-specific reports. However, the data collection is limited, especially for floating turbines, as it is based on pilot parks — not on future solutions. It is therefore difficult to verify the calculations to form an accurate picture of how the various factors have influenced the cost estimates.

Suggestion of two different rankings

In further evaluations of the areas, it may be useful to create two rankings; one based on natural conditions such as wind resources, seabed conditions, and distance to shore, while the other on available technology. This would make it easier to adjust the rankings as technology develops.