Wind turbine controlled demolition

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.

Multirotor wind turbine: an update

Some time ago I wrote a post about the interesting concept of multirotor wind turbines, including the full scale prototype built by Vestas with 4 refurbished V29-225kW (that is, with a 29 meters rotor diameter).

It has been installed in a test site of the Technical University near Roskilde, in Denmark - I believe I’ve been there many years ago for the famous rock festival.

After running for approximately 3 years the prototype has been dismantled. The result of the test are still not public, but some information leaked.

For instance, an increase in annual energy production (AEP) of approximately 1.5% has been reported. It is due to an improved power curve, allowing the turbine to reach faster the nameplate capacity.

I’m not sure this result can be scaled to the current turbines in the market – however for a modern WTG a 1.5% increase is a lot of money.

Another counter intuitive fact is that the wake effect (the turbulence generated downstream by the WTG when the wind cross the blades) is minor in a multirotor. Don’t ask me why because I’m not an expert in fluid dynamics.

Additionally the load increase is not significant. That is good, because it has a direct impact on life expectancy of the turbine and on tower and foundation cost.

Moreover noise emission is not significantly higher. This point is especially relevant in Europe or other area with strong constraints in term of noise.

What happen to decommissioned wind turbines?

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.