Though wind power is an important source of sustainable energy, the cost of installing turbines has always been an obstacle to more widespread adoption. This is particularly true for offshore wind farms, which require large, high-tech turbines to be constructed and maintained in oceans and lakes.
To address this challenge, an innovative offshore turbine construction process has been developed by the ELISA project. ELISA’s 5-MW operational prototype is the first bottom-fixed offshore wind turbine completely installed without the need for costly and scarce heavy-lift vessels.
‘The ELISA technology is a pioneer in the development of completely self-installing offshore turbines,” said Project Engineer, José Serna. ‘The entire system is completely pre-assembled and pre-commissioned in controlled harbor conditions, enhancing the possibilities for industrialization and minimizing risks related to offshore assembly work.’
The ELISA 5-MW prototype uses a gravity-based foundation, which serves as a floating platform from which an automatic telescoping tower is anchored, complete with a wind turbine. Each unit – platform, tower, and turbine – is assembled onshore. It is then towed to its open-water site, using conventional tugboats, and secured. Next, the tower is raised.
“It’s important to note that currently there are only three or four heavy-lift vessels in Europe capable of installing an 8-MW turbine in waters deeper than 40 meters, and Europe leads the way in comparison to other developed markets,” said Serna. “In other words, this system will also be a key European export to such markets as the U.S. and Japan.”
What’s particularly unique about the system is that the telescopic configuration of the tower was designed to bring down the unit’s centre of gravity, meaning the platform serves as a self-stable floating barge from which a work crew can preassemble the entire system inshore. Building the structure inshore reduces the costs and risks that often accompany the assembly of open water wind turbines.
‘This vessel-free installation capacity is not only a source of large cost reductions, but also a way to support the clear trend towards larger offshore wind turbines, a key step in improving a wind farm’s cost of energy,” explained Serna.
Once tugged into its out-at-sea position, the platform is ballasted to rest on the seabed. Once secure, 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, and then are reused to lift the next level, and the next, and so on until fully erected.
Furthermore, jacks are supported by ones below, which also guides the hoisted tube as it rises in a self-installing manner, where the tower itself is the only supporting structure required. And all of this is done from a single access platform.
“ELISA will allow for drastic cost reductions in the substructure supply and in the installation costs of offshore wind energy, which is set to play a strategic role in Europe’s evolution towards a low-carbon and locally sourced energy mix,” said Serna. “As a matter of fact, the cost per megawatt of the prototype being developed is already below current market prices, despite all the investment required in auxiliary infrastructure and means whose complete costs have been dedicated to a single unit.”
According to Serna, the ELISA system can significantly reduce costs by as much as 30 to 40 % compared to traditional technology based on jackets or XL Monopiles. It also saves users on maintenance and upkeep.
Thanks to ELISA’s robust, durable and fatigue-tolerant and maintenance-free concrete substructure, researchers claim the system will improve the integrity of the structure and reduce operational costs. As an added bonus, the system is noiseless and more environmentally friendly than steel alternatives with regards to its impact on sea life and carbon footprint.
Filed Under: Construction, News, Offshore wind, Towers, Turbines