Researchers involved in the EU-funded ELISA Project have developed an offshore wind turbine system that can be completely pre-assembled and pre-commissioned in controlled harbor conditions. A fully operational 5 MW prototype located in the Canary Islands is the first bottom-fixed offshore wind turbine completely installed without the need for heavy-lift vessels.

A gravity-based foundation is combined with a telescoping tower. Image source: ELISAA gravity-based foundation is combined with a telescoping tower. Image source: ELISAA gravity-based foundation serves as a floating platform from which an automatically telescoping tower, complete with wind turbine, is anchored. Platform, tower and turbine components are assembled onshore, after which the unit is towed to its open-water site using conventional tugboats, where the platform is secured and the tower raised.

Once the platform is ballasted to rest on the seabed, the tower is lifted to its final position via cables and conventional heavy-lift strand jacks. These jacks start by lifting one level of the tower at a time and are reused to lift successive levels. The jacks are supported by the one below, which also guides the hoisted tube as it rises in a self-installing procedure where the tower itself is the only supporting structure required.

The telescopic configuration of the tower was designed to lower the structure’s center of gravity, so that the platform serves as a self-stable floating barge from which the crew can preassemble the entire system onshore. This process reduces worker risks that often accompany the assembly of open-water wind turbines, while heavy vessel-free installation results in large cost reductions. Project engineers indicate the ELISA system can significantly reduce costs by as much as 30-40% compared to traditional solutions based on jackets or XL Monopiles.

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