I have discussed in another article the challenges associated with the disposal of the blades when a wind farm is decommissioned or repowered.
But what happen to the foundations?
The destiny of a foundation will depends on local regulations, on the environmental requirements that are normally given with building permits and on the wish of the owner of the wind farm and of the land.
As a general rule, foundations are at least partially dismantled. The first centimetres (20, 50 or even one meter) are removed and the rest of the foundation is left in place and buried below a layer of organic soil.
Sometime the entire foundation is removed. This is a complex activity, and blasting or at least many hours of hydraulic hammer are needed.
The third option is to bury the foundation below a small hillock.
In case a repowering is planned there is also a fourth and more interesting possibility: giving a second life to the old foundation integrating it in the bigger, new foundation. There is a group of company that is studying this possibility under the name “FEDRE” (Fondations d’Eoliennes Durables et Repowering – French for “Long lasting wind turbine foundations”).
The concept that is being developed is how to reuse part of the existing footing for the new foundation - adaptation the existing one on the short term and working with reusable foundations designed ad hoc on the long term.
In case the foundation has to be dismantled some difficulties may be experienced.
They are very “dense” in steel (on average a foundation can easily have more than 100 Kg of steel for each cubic meter of concrete). Due to the concentration of rebars in some areas of the foundation (above all, in the centre) it can be more difficult and time consuming to separate the steel from the concrete.
Usually steel is separated from concrete and melted again. In some countries the reinforcement bar are even used “as they are” without being melted and reformed (i.e. they are straightened and used again in another structure).
The presence of steel makes more complicate grinding the foundation in smaller elements to use it again as a construction material, for instance to build roads (in the nucleus of the embankment) or for earthworks as a filling material.
It is worth mentioning that some with turbine have concrete tower or hybrid (concrete + steel) solution. They could be equally difficult to recycle.
Repowering and decommissioning will probably gain momentum in the near future.
2018 and 2019 saw only a few hundreds of MW decommissioned (unsurprisingly mostly in Germany, where the installed capacity is huge). However the numbers should increase steeply in the next years when more and more wind farms will end their 20 years of supported tariff.
Unless they are able to close some king of PPA (power purchase agreement with a counterpart willing to buy the electricity at a certain price) it could prove to be not economically viable to sell the power at spot prices.