Self-installing offshore turbine to be tested in Canary Islands
A number of gravity base turbine foundations are being developed in Europe, as are concepts for combined foundation and tower units that can be manufactured ashore and towed into place. However, few seem as advanced or as promising as a Spanish concept for a self-buoyant precast concrete foundation that can be installed without the use of cranes, which is due to be tested next year.
The Elisa self-installing turbine concept was developed by a consortium led by Esteyco Energia. The Elisa consortium plans to install a prototype of the foundation and tower off the island of Gran Canaria. Manufacturing of the foundation was carried out in a drydock at the Port of Arinaga. Once it is completed, the entire assembly will be transported to its final location at the Oceanic Platform of the Canary Islands (PLOCAN), where it will be installed, early in 2017. Esteyco Energia says the prototype is due to be operational in the summer of 2017. The project is being part-financed by European funds from the Horizon 2020 programme and partly by the consortium itself. The prototype has been dimensioned to take a 5 megawatt (MW) offshore wind turbine, thought to be supplied by Adwen. The consortium describes it as the first bottom-fixed offshore wind turbine installed without the need for heavy-lift vessels, although other similar concepts are under development elsewhere.
“Elisa is pioneering the development of a completely self-installing offshore turbine,” said project engineer José Serna. “The entire system is completely pre-assembled and pre-commissioned in controlled harbour conditions, enhancing the possibilities for industrialisation and minimising risks related to offshore assembly work.”
The Elisa prototype uses a gravity-based foundation and an innovative telescoping tower. Each unit – including the platform, tower and turbine – is pre-assembled onshore and then the entire unit is towed to its open-water site using tugs, where the platform is secured to the seabed and the tower raised. One important advantage of the telescopic tower is that, when lowered, it lowers the overall unit’s centre of gravity, which enhances the platform’s stability. Being able to build the structure ashore reduces the risks inherent in assembly at sea. Once tugged into position, the platform is ballasted to the seabed. When secure, the tower is raised to its final position, with each new level of the tower lifted sequentially until it is fully built.
“It is important to note that, currently, there are only three or four heavy-lift vessels in Europe capable of installing an 8MW turbine in waters deeper than 40m, and Europe leads the way in comparison to other developed markets,” said Mr Serna, noting that the Elisa concept could therefore be applicable to export markets such as those in the US and Japan.
“Vessel-free installation not only reduces costs,” said Mr Serna, “it also provides a way to support the clear trend towards larger offshore wind turbines, which is an important part of reducing the cost of offshore wind energy.”
“Elisa will allow for drastic cost reductions in the substructure supply and in the installation costs of offshore wind energy,” Mr Serna claimed. He said the cost per MW of the prototype being developed by the Elisa consortium is “already below” current market prices, despite all of the investment required to build the prototype.
Mr Serna believes the Elisa concept can reduce costs by as much as 30–40 per cent compared to conventional solutions based on jackets or extra-large monopiles.
The consortium says the robust, durable, fatigue-resistant and maintenance-free concrete substructure (shown here at Arinaga Port, in Gran Canaria, where it was built) will enhance the integrity of the structure and reduce operating costs. An added bonus is the fact that, unlike monopiles, which need to be driven into the seabed, installation of the Elisa self-installing foundation is almost noiseless and much more environmentally friendly.
Esteyco’s partners in the project are ALE (which is responsible for heavy lift operations), Adwen (turbine manufacturer) and DEWI (who are responsible for instrumentation and monitoring).