MagnaDense keeps Hywind turbines floating upright

LKAB Minerals supplied high density MagnaDense for Hywind Scotland, the first commercial floating wind park.

A floating spar-type platform with anchors to the seabed is the design-base for this concept. However, the floating spar’s turbine is much taller than the hull. Also, it has a moving rotor that harnesses the strong offshore winds in the North Sea.

The waves, currents, and winds are strong external forces. Therefore, keeping the very heavy and tall floating wind turbines upright in the open sea is a big challenge. You need a lot of weight to achieve a low centre of gravity in the structure.

This solution involved the use of LKAB Minerals MagnaDense as a loose ballast. In addition, our customer used MagnaDense to produced high-density concrete with a density of 4t/m3. They use this concrete as a counterweight. This aids the installation process and adds to the overall weight of the structure.

Ballasting completed and Hywind now in operation

First, the high density concrete is produced and placed within the substructure at the Navantia wharf in Spain. Next, the construction is transported to the Hardangerfjord, offshore Stord, Norway. After uprighting and water ballasting of the foundations, a company installed the MagnaDense loose bulk ballast in the floating foundations.

Following this operation, the tower and turbine were mated to the substructure. Finally, they towed the structure out to its final destination in the Scottish waters. Each construction got a ballast of approximately 5,000 tons of the dense aggregate. And each foundation also got an additional 1,100 tons of concrete ballast.

The five turbines of this first commercial floating wind farm are now producing electricity on the Scottish coast.

To lower the centre of gravity our customer used the  >27,000 tonnes MagnaDense as loose ballast. This also keeps the wind turbine upright. It was of vital importance to stabilise the foundation. It ensured that sea waves and currents did not affect it.

Hywind design enabled by MagnaDense

Statoil’s Hywind pilot project offers a fresh and unique concept to the energy market; the first commercial floating wind farm of its kind in the world.

The Hywind tower rises 176 meters above the water surface and has blades with a span of 75 meters. It is awe-inspiring and much larger than conventional and typical wind turbines in use. The sheer size means that it will also be able to generate more power. The total energy production of up to 6 MW/each is enough to power 20,000 households in total. Key to producing energy and utilising as much of the capacity as possible is strong and constant winds. A placement further out from the coast makes this possible. Here the waters are deeper and to realise the ambitious goals of the project they needed the floating design.

More weight, less volume

In the case of Hywind Scotland, MagnaDense offered the best price/quality for the chosen design. Given its high specific density and excellent compaction properties, it results in more weight in less volume. MagnaDense complies with the EN-12620 standard for concrete aggregate. It produces high quality and high density concrete, making it ideal for the bottom ballast that functions as a counterweight.

Sustainable material for renewable energy projects

We manufacture MagnaDense aggregate from the natural iron oxide, magnetite. It is chemically inert in marine conditions and does not leach, supporting the sustainability aspects of the Hywind project. In fact and proving the point, we have even repurchased material. The magnetite had been in use for 22 years in Shell’s ‘Draugen’ Floating Loading Platform. The MagnaDense was commissioned at an oilfield 150 km offshore from the Norwegian coast. The reclaimed material was tested and compared with the original shipping analysis that proved the material chemically to be unchanged. With this assurance, the material was again offered to the market and reused as a concrete aggregate.

Returning over-supply

We offered a value-added service to support the financial sustainability of the project; allowing our customer the opportunity to return the over-supply of MagnaDense upon completion of the project. This ensured that costs were controlled and prevented any spoil of unused product.

Important considerations for choosing a ballast supplier

When looking at the cost of a wind project this will, of course, vary with project and circumstances. The cost of High Density Aggregates is often a smaller part of the total project. However, good quality high density material ensures negative buoyancy and prevent costly re-work, uncertainty, and project delays. This is due to the consistent density, particle sizes and no impurities.

On-time delivery will also be key, and should not be an overlooked factor. You should not only consider the aggregate costs. Any delay caused by product deficiencies or late deliveries might cause time delays and penalties for parts of the projects. These impacts might result in a very costly bill. In addition sustainability, pricing and service are important considerations.

Leading global supplier

Based on these criteria LKAB Minerals have positioned themselves well and are a global leading supplier to the industry. Our MagnaDense offers ideal properties; we produce this in sizes for industrial use and we characterize the product by high particle density and high submerged weight. On top of that LKAB Minerals can deliver large volumes and consistent quality.

Lastly, our company has a proven track record. And prides itself in being a reliable partner with the confidence to deliver what they promise for any project; all contributing factors in winning the supply contract for aggregates to the Hywind project.

For a detailed Case Study on the Hywind project please contact us. You can also watch a short (<1 min) movie about using MagnaDense in this project.