A tube with a length of between 15 and 20 metres is placed into the ground (with a vibrating tool), which is then filled with liquid concrete and reinforcement bars. Then the tube is removed, also by means of vibration. This creates in-situ formed piles. A combination of alternate vertical and raking piles is created, which is better able to absorb the enormous forces exerted on the foot of the turbine.
The foundation (squirrel-cage rotor) and formwork are attached to the vibrated piles; this is made up of around 100 tonnes of iron, which is then filled with around 800 cubic metres of concrete. To seal the concrete, i.e. to remove all the air from it, we use pokers. After several days, the formwork can be removed and, after around a month, when the concrete is fully cured, the superstructure, in other words the wind turbine itself, can be erected.
A project of national importance
Generating green energy forms part of the climate goals for the Netherlands. In the Regional Wind Energy Plan, the authorities in Flevoland have opted to cluster wind turbines in large-scale projects. Windplan Groen is the framework for this in the eastern part of Flevoland. Windkoepel Groen is the driving force behind this plan. Windplan Groen was developed by the combined efforts of the instigators, government agencies and other important partners. The starting situation was benchmarked in the Regional Wind Energy Plan that was agreed in 2016 by the regional authorities. As the plan envisages energy yields in excess of 100 MW, it qualifies an RCR project under the auspices of the Ministry of Economic Affairs (together with the Ministry of Infrastructure and the Environment).
Research has shown that the energy that is needed to produce a wind turbine, erect it and maintain it can be recouped in three - six months of operation. After that, the wind turbine goes on to produce clean, CO2-free energy for at least 20 years.
During construction of the wind turbines a small amount of nitrogen is emitted, but the wind turbines will subsequently make a significant contribution to reducing nitrogen emissions in the Netherlands. During the two-year construction period for the new wind turbines in Windplan Groen, construction traffic and building work will emit around 3400 kg of nitrogen per year. During the service life of at least 25 years, use of the turbines will save more than 740,000 kg of nitrogen each year. That means that over a period of 25 years, many times more nitrogen emissions will be prevented than emissions caused during construction.
In order to neutralise nitrogen emissions during construction, agreement has been reached in negotiations between the authorities and two commercial parties on withdrawal of permits and amendment of the local development plan in relation to intensive livestock raising. The nitrogen emissions thus removed more than compensate for the emissions that are generated during construction of the wind farm. This is enshrined in law, and is a robust solution to the challenge that had been created when the PAS (nitrogen action programme) was declared to be invalid by the Council of State.