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Spotlight on VALID user cases: IDOM's Wave Energy Converter

2nd deployment of IDOM's MARMOK-A-5 device at BiMEP

The cornerstone of the Horizon 2020 VALID project is its three user cases, against which the methodology and associated hybrid testing infrastructure will be validated. In this three part series, we break down the different wave energy devices used and their role in the VALID project.

Electric generator failure, a crucial issue of wave energy devices, is the focus of VALID User Case II. Using IDOM’s floating device, the Mutriku fixed Oscillating Water Columns pilot plant and TECNALIA’s test rig facilities, the VALID project aims to further understand and evaluate failures in generators and power electronics that operate about 20% of the time over nominal power.

To obtain energy from the waves, it is necessary to achieve a relative movement between two elements. However, this relative movement is problematic because of the large structural loads that occur under extreme environmental conditions.

IDOM's solution is the Oscillating Water Column (OWC). In this technology we have a single structural body made up of a hollow cylinder, and the second element is the column of water inside it.

Diagram of the operation of a WEC based on OWC technology

Both elements are designed to resonate at the wave frequency and to do so in a push-pull motion. The relative movement of the structure and the water column produces an air chamber of variable volume. By means of a turbine, the energy of the air that enters and leaves the chamber is converted into electricity.

In this way, the only moving part is the turbine that is out of the water, which makes the system extremely robust, increasing availability and reducing maintenance costs.

Still, the generator turbine has to work with oscillating power and high peaks in the most energetic sea conditions. This way of working is not what generators are designed for and can cause an early failure.

As part of the VALID project, IDOM and WP4 partners will study the loads to which the generator is subjected, and the way this accelerates its degradation, with the aim to improve the way of selecting the generator and operating it during its useful life.

Transportation of MARMOK-A-5 from the shipyard to BiMEP

Article written by Patxi Etxaniz of IDOM's Advanced Design & Analysis Department.

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