PO056

World's first craneless bottom-fixed offshore turbine. 5 MW ‘ELISA’ prototype

JOSE SERNA 1, JAVIER NIETO1
1ACHE, MADRID, Spain, 2IABSE, ZURICH, Switzerland, 3SPANISH ASSOCIATION OF CIVIL ENGINEERS, MADRID, Spain

Abstract

The ELISA 5MW prototype, which is currently under construction in the Canary Islands and will be fully operative in May 2017, is set to become the first bottom-fixed offshore wind turbine completely installed with full independence of costly and scarce heavy-lift vessels.

The ELISA technology involves a novel self-floating GBS foundation system which integrates an autolift telescopic tower, and can be fully assembled on harbour. The telescopic configuration of the tower brings down the center of gravity during the towed self-floating transport, allowing the bottom foundation platform to temporarily act as a self-stable floating barge over which the complete system can be preassembled inshore.

Once ballasted to rest on the seabed, the tower can be lifted to its final position by means of cables and conventional out-of-the-shelf heavy-lift strand jacks which are reused to lift each tower level successively. All works are carried out from a single access platform.

Expected cost reduction capabilities -as due diligenced both by reference developers and offshore turbine manufacturers- exceed 35% when compared to Jackets or XXL Monopiles in deep (35m plus) water. It is a system which is also excellently suited for the next generation of offshore wind turbines thanks to its direct scalability, based only on conventional and readily available equipment and means. The 8MW substructure is based in the same principles and readily available means as the 5MW, and so will the 12MW when it arrives.

Method

The technology has been developed and certified following all the steps along the Technology Readiness Level (TRL) typical path. Apart from the different stages of design, extensive tank and lab experimental demonstration have been completed. These have included multiple tests of the installation process and means in different metocean conditions, extensive monitoring of temporary and operative performance and a full design and construction certification.

A significant step, worth highlighting among these, was the construction of a full scale testing prototype of the telescopic tower for the tuning and demonstration of the autolift system.

In short, the prototype culminates a 7-year development and demonstration process, which has been supported by reference R&D institutions such as CDTI and the Horizon 2020 program by the EU commission.

Results

All these experimental de-risking initiatives have proven very successful, and the result is the fully operative offshore prototype, which demonstrates both the feasibility of the construction and installation process and the cost reduction expected for the technology.

It is worth highlighting that in the offshore wind market there are not concrete towers. This 1:1 scale prototype will be the first one. Steel offshore towers require heavy-lift vessels for installation, since the complete tower is transported from the coast. These vessels are very expensive and scarce. This limitation (high risk/cost + low availability) is solved with the technology implemented in the ELISA project.

Conclusions

The presented ELISA technology will have a significant impact in the offshore wind industry as it provides:

Objectives

In the quest for a lower LCOE of offshore wind energy, which has reduced dramatically in the last years, the technology presented shows that there is room to continue reducing construction and O&M costs.

It also shows introduces: