An interesting video on the use of concrete towers in Chile. Among the benefits of this solution the creation of local jobs (several hundred for factory) and the increase of local content (the amount of goods and services provided locally, an important parameter in some tenders).

Concrete towers are especially cost effective when the hub height is over 100 meters. Additionally they are less prone to price variation - steel prices, at least in Europe, dropped in 2016 to rebound in 2018.

Finally transport cost are usually lower, at least if the factory is located near the wind farm as it is usual.

A reader of the blog shared the link of this video, showing the controlled demolition of a wind turbine in the UK.

The turbine looks like an old Acciona Windpower model. As you will see, the turbine is connected using a rope to a back hoe and the base of the tower is slowly cut using a blowtorch.

Then the backhoe start pulling, and the turbine fell to the ground pretty much like a tree.

I am aware that this solution has been used in several wind farms in different countries. However, I believe that this method is questionable. I have two concerns:

• Environmental impact. Not only the turbine destroy a bunch of trees but above all after the impact with the ground the debris flight everywhere. I assume that the area can be cleaned afterwards – however filling the area with fragments of different materials looks like a suboptimal solution to me.
• Safety risks. You will notice that at the minute 3:00 one of the blades hit the ground and detach itself from the rest of the turbine, moving in the direction of the backhoe. An objection can be that the rope can be long enough – however giving the geometry of the turbine and its different materials, I still see the residual risk of flying fragment hitting the operators.

I would recommend the “component by component” dismantling. We used this solution in a wind farm in Portugal and I believe it is much safer.

To see an intermediate solution (partial dismantling and partial demolition), have a look at this other video.

It is the repowering of El Cabrito, a very old wind farm near Tarifa (south of Spain). By coincidence, that area is also one of my preferred holyday destination, so I have several pictures of the old turbines.

You will see how the crane dismantle the blades and the nacelle. Subsequently, a different tool is used to crash the tower.

In a previous post I mentioned my experience with a repowering (a wind farm where the old turbines are exchanged with new models to increase the production and lower the maintenance costs).

But what happen with the old turbines when they are dismantled?

For some of them there might be a new life. There is a market for second hand turbines – some years ago I met one guy who purchased a bunch of old WTGs (I believe they were in the 200 KW range) and made his own wind farm with a very reasonable investment.

However the majority of decommissioned turbines are scrapped. This bring some challenges because not all components are so easy to recycle.

In order of complexity I would say that the least problematic element is the tower – it’s usually made of steel and it can be easily sold at the current market price.

The foundation is another element that can be left untouched below ground or demolished. The resulting material can be used again in construction, for instance in a road embankment, sub base or even as aggregate in new concrete elements.

I’ve also seen a very interesting technical solution where the old foundation becomes part of the new one – in this case you will need to have both the new and existing turbine at the same coordinates.

The nacelle has several different elements, including some that are potentially contaminating (e.g. the oil of the gear box). More complex to recycle but still doable.

By far the most challenging components are the blades. Usually they are made of composite materials – steel and glass or carbon fibers reinforcement in a polymer matrix. Usually this matrix is thermoset, meaning that the polymers are cross linked (that is, it will be very difficult to separate the elements).

The difficulty start from the logistic. Blades are very long elements: the old are around 20 meters, but recent models are already above 50 meters and they need special trucks to be moved. Theoretically you could chop them into pieces before transportation but the tools could not be easily available, and I also see some safety risk in cutting blades on site.

The following problem is what to do with them: as mentioned there separating the components is not simple, so today many blades ends in a landfill. Alternative solutions are currently being investigated but it’s still challenging to find a cost effective solution.

There are also alternatives uses: in northern Europe (Netherlands, Denmark, France) there are several architectural projects made using old blades, such as kids playground, bus stops, seats and even bridges.

At the beginning of the year I’ve had the pleasure to work at my first repowering EPC – Vergao, in Portugal, together with Generg (a big local player).

This is supposed to be one of the many projects that should materialize during the next years. My former manager Luis Miguel thinks that repowering is “the next big thing” in wind energy.

I agree with him that sooner or later it will kick off. In theory, wind turbines are designed for a life of 20-25 years. Through heavy maintenance and substitution of the main components (e.g. gearbox) it can be probably extended a bit more. This practice is called life extension or retrofitting.

However, at the end of the day the question is: does it make sense to keep running old turbines? Or it’s more cost effective to install new WTGs?

Older wind farms are usually in incredibly windy site (class I, according to the IEC classification) and are probably using turbines of less than 1 MW.

Therefore it will be possible to reduce the number of installed turbines (a ratio of 3 old for 1 new would not surprise me) and even so increase the total production.

What can sometime hinder the repowering is not the availability of a better technical solution – and it’s often not even a problem of financing. What can complicate the picture are difficult legal frameworks, low social acceptance, environmental constraints , etc.

In theory, there are scenarios where the best solution will be to dismantle the wind turbines and scrap them (or sell them to third world countries).

Coming back to my personal experience, working at a repowering has been a very interesting professional experience.

There are quite a lot of unusual challenges, as the existing WTGs have to be dismantled while in parallel new ones are erected. This makes the time schedule more complicate than usual, and bring new health and safety challenges due to the many teams working at the same time.

I’ve also had the opportunity to look into new topics, like the possibility to “recycle” the existing foundation incorporating it in the new one (yes, you can do it), the market price of used turbines or the environmental requirements linked to the dismantling and scrapping of wind turbines.