Concrete is the Future for Offshore Foundations

Abstract

This paper compares the costs of using concrete foundations against steel monopile foundations for offshore wind turbines, and argues that concrete foundations will be cheaper. Most offshore windfarms have steel monopile foundations, but in Denmark concrete gravity foundations have been used with success. Two projects have tendered for steel monopiles and for concrete foundations and have implemented the concrete foundations that proved cheaper. No project has tendered for both foundation concepts and chosen steel monopiles. Nysted Offshore Windfarm with concrete foundations has the cheapest foundations of any offshore windfarm so far. A conceptual foundation study carried out for the London Array West Offshore Windfarm indicates that the same method and very low-cost foundations as for Nysted can be used. Optimised design of light-weight concrete constructions is the key to low-cost installation. Cheap manufacture can be carried out near the site or at even lower cost in Eastern Europa from where it can be shipped at little extra cost. The main construction of steel monopile foundations will become twice as costly as of concrete gravity foundations, and though installation is more costly for the gravity foundations it seems most likely that tendering between steel monopile and concrete gravity for London Array West will prove concrete considerably cheaper. It is argued that these considerations are to a wide extent generally valid, and also for very large turbines in deeper water. Concrete foundations will in 2006 be installed at Lillegrunden Offshore Windfarm in Sweden, and at Belgian Thornton Bank in 2006–7. So indications are strong that concrete is the future for offshore foundations.

A floating platform of concrete for offshore wind turbine

“…In Europe, the building price for reinforced concrete construction is about 200e/ton. 16 So, the building cost will be 1.5 Â 10 6 e for the present platform. In addition, the building cost for the mooring system is estimated to be 1.0 Â 10 6 e for water depth less than 100 m. 8 This corresponds to 0.5 Â 10 6 e/MW for the complete design-and-construct foundation supply, which is comparable to the present cost of bottom-fixed offshore wind foundations.…”

Design Optimization of Conical Concrete Support Structure for Offshore Wind Turbine

“…The wave force f per unit length of a fixed vertical cylinder that has a diameter D is expressed by Equation (1).…”

“…Concrete is more cost-efficient than steel because it has a low material cost. Referring to tender results of two projects named Middelgrunden and Nysted [1], market response in both cases very clearly showed that a concrete solution could be manufactured and installed at a lower price.…”

Energy From Offshore Wind

“…Gravity Base Suction Bucket water depth as well, although the use of concrete may provide some advantage in extending favorable economics [13]. Gravity base foundations require significant preparation of the seabed to assure a level substrate within 20 mm, however, installation effort is reduced once this preparation is complete [14].…”