New conceptual design for offshore wind power substations

The new offshore wind power substation project, Marin-el, was presented on 17 December at an event held at the Higher School of Naval Engineering (ETSIN) at the Universidad Politécnica de Madrid (UPM). The project is headed up by Iberdrola and backed by the Government of the Basque Country with a project consortium featuring the participation of the Tecnalia technological centre and the Construcciones Navales del Norte (La Naval) shipyard among other firms from the naval and renewable energies sectors.

The event was attended by Cristina Heredero, director of Renewables Technology and Sustainability at Iberdrola; Ignacio Pantojo, project coordinator; Luis Pedrosa, director of the Energy and Environment Division at Tecnalia; Elías Hidalgo, head of the Marin-el Project at La Naval; and ETSIN professors Luis Pérez Rojas and Ricardo Zamora.

The Marin-el project focuses on creating a new type of substation based on the needs of offshore wind farms of the future, optimised to operate in the North Sea, with reduced installation and transport costs and adapted to different depths and types of sea beds. It is designed for wind farms generating around 500 MW, situated some 50 km offshore and at depths of 50 metres.

Given the trend for locating wind farms at greater distances from the coast, larger capacity wind turbines at greater depths, this project aims to standardise and innovate technology to meet today’s challenges in offshore wind power. The main aims of this project are to strengthen Basque industry at the same time as creating a self-installable unmanned installation, in other words, a substation that can be remotely operated and installed thereby minimising the use of special vessels that have major repercussions on both the budget and installation schedules.

The design concept encompasses:

• The topside which houses the substation containing all the electrical equipment needed to transform the energy produced before it is transported to land.
• The self-hoisting system comprising 6 feet integrated into the topside that slot into each other and is positioned over the jacket, raising the topside above sea level through its vertical movement.
• The barge to transport the topside from the mainland to its location at sea where it is positioned over the jacket.
• The jacket: a lattice structure that rests on the sea bed and provides the base for the topside. It forms part of the foundations and its type will depend on the depth of the water.

This is a flexible design created to be able to replace the jacket with a gravity platform or other system or even anchor it directly to the sea bed.

Unlike other substations, this concept replaces the substation buoyancy module with a reusable barge thereby reducing the overall weight of the structure.

The topside concept where the substation will be installed comprises four housings: the cables housing; the housing that contains all the electrical equipment; the housing with all the auxiliary services and additional services needed in the event of employing operators; and the helipad housing.

The presentation of Marin-el at the ETSIN included two simulations of the testing that has been undertaken these past months at the School’s hydrodynamic experiences canal to study its behaviour at sea.

The first simulation was a tugging test. As the barge is not self-propelled, this test is carried out to ascertain resistance to forward motion to then determine the characteristics of the tug that will be required to tow it out to its location. The test was performed by towing a 1:48 scale model in calm waters and at varying speeds.

The second simulation is the installation test that evaluates the movements of the model by the waves generated in the canal in order to study limitation vs. accelerations. In other words, to identity the maximum structure accelerations that allow the team to perform the substation installation activities on the jacket. To do this, a scale model of a jacket was built and placed on the bed of the canal above which the barge transporting the substation is positioned, mooring it with lines to simulate the bollard pull of tugs at sea.

In addition to these tests, whose simulation formed part of the presentation, tugging tests in waves and installation tests under extreme conditions during the months of November and December were performed at the ETSIN canal. These tests will continue during January 2016 in the tank at UPM’s School of Civil Engineering.

During the tugging test in calm waters, a significant wave height of up to 3 m was taken into account, with wave periods of between 6 and 12 seconds and speeds of between 3 and 8 knots. During the installation test, the significant height was 1.5 m; and in the extreme conditions test, the wave height was up to 14 m with wave periods of between 12 and 16 seconds.

The consortium, headed up by Iberdrola, includes Ingeteam, Ormazábal, Arteche and OASA, companies that offer innovative solutions for substations. La Naval is responsible for carrying out works to improve the manufacturing process, designing the barge and the manufacturing process for both the topside and the jacket. Tecnalia is providing support to the design of the substation, the transport barge and the jacket.

The project encompasses several important aspects. On one hand it addresses the transport and installation design of the substation, barge and jacket, and on the other, the updating of electrical designs to achieve a reduction of 15% in the size of the substation with the aim of creating a smaller, simpler and more economical substation.

The project also includes an assessment of the environmental impact of the proposed substation through a life cycle analysis carried out via a tool to study the life cycle of each of its components.

All this is combined with the goal of making savings in energy costs, by means of an eco-design that uses less critical and lower energy consumption raw materials.

The next phase of the project takes into account costs reduction (manufacturing optimisation, improved equipment) and risks reduction (reducing the number of feet of the self-hoisting system from 6 to 4 and increasing the significant wave height at the installation). Lastly a business analysis will be carried out.

The final results will be presented in May 2016.