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The demand for offshore wind is growing as Europe transitions towards using more green energy supplies. Wind farms situated further out to sea generate electricity more reliably than those on land or nearer the coast. They are also less visible and do not lead to land-use conflicts. However, placing turbines in deeper waters is costly and difficult. Using existing technologies, around half of the project cost goes towards installation.
The EU-funded ELISA project has come up with a solution to this by developing a new type of substructure to support wind turbines. Project engineers have designed, built and demonstrated a self-buoyant pre-cast concrete foundation which – with a telescopic tower – can be easily towed out to sea.
‘Everything is manufactured and assembled in harbour, including the telescopic tower and turbine which sit on the ELISA base,’ explains chief technology officer José Serna from Esteyco SA, Spain. ‘The structure can be towed by conventional tugboats to its final position and then, with the aid of an auxiliary system, ballasted to the seabed.’
Solid foundations
Installation is therefore completed without the need for heavy lifting vessels, which are in great demand and costly to hire. Using the ELISA concept could help reduce the cost of offshore turbine installation to around 15 % of the project cost.
The foundation can be used in waters up to a depth of 60 metres and is designed to last about 50 years, which is well above the 25-year lifespan of current wind farms. Because it is made of prefabricated concrete rather than steel, maintenance costs will be lower – steel foundations need replacing every five years.
The base is suitable for most soil conditions, including soft and rocky seabeds. ELISA is also more environmentally friendly than current alternatives. According to the project team, using concrete and constructing locally could potentially reduce the carbon footprint of their solution by up to 75 % compared to equivalent steel alternatives. In addition, placing turbines further out to sea reduces their impact on marine life.
Working prototype
ELISA is closely linked to the EU-funded ELICAN project, which has gone on to develop the top section of the structure, the self-installing telescopic tower that can support a 5-megawatt prototype turbine. Both the ELISA and ELICAN concepts have been successfully tested together in waters off the Canary Islands.
The complete package of ELISA technology – which includes the ELICAN innovations – is already attracting commercial interest. ‘Since final installation of the prototype in June 2018, we have been approached by several players, including developers, procurement and construction companies,’ says Serna. ‘The likely next step is to develop a series of towers and turbines in a limited number of positions so as to consolidate the solution and fully open the gates to commercial development.’