Monthly Archives: September 2018

Wind farm construction steps: generic timeline infographic

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One of the pleasures of fatherhood is the fact that you have quite a lot of extra times during the night – if your kids do not sleep.

Yesterday night has been exceptionally short due to a son diving out of the bed and hitting his head and another who decided that at 6 AM the night was ended.

Therefore I’ve used this extra time to create a timeline with a very generic overview of a small wind farm construction steps.

They can (and do) vary a lot between a project and another. However it should give you a rough order of magnitude of the key steps and the time needed for each of them.

The editable PPT file is available on demand. It’s based on a free template made available by Hubspot (thank you guys!).

Enjoy!

Target Price for BoP: a basic introduction to a complex topic

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There is an old joke that say something like “What happens when you put 10 economists in a room? You'll get 11 opinions.”

My experience with Target Price is similar: I’ve heard many opinions in favour and against it and probably in general it’s not “right” or “wrong", but it's a strategy that, depending on the context, can be more or less appropriate.

Basically, the idea is to share with the subcontractors the price level that they are supposed to reach – or if you want to see it the other way around how much you can afford to pay to build the wind farm.

On a smaller scale the idea is not new. It is what happen when you ask someone if they can meet a certain budget, for instance asking to an artist “Can you do me a portrait for 100$?”. The answer could be for instance something like “Yes, but the dimensions will be 20x20 cm”

There are indeed some arguments I can see in favour of it:

  • BoP is (partially) a custom service with certain technical specifications that in some cases can be changed.

The implication is that the input of the subcontractor can be requested to hit the target, or some initial requirements can be changed. A classic example is the level of redundancy of the substation: fail proof solutions are not cheap.

  • Material costs can be clearly identified (in some cases).

This is for instance the case when items like medium voltage cables are purchased - a key driver in the cost of cables is the spot price of the raw materials (copper, steel, aluminium) so it’s relatively easy to calculate how much you should pay.

However, it’s also easy to find arguments against it:

  • To give a target price, the buyer should understands the cost structure.

This is not so easy as sit might seem: people dealing with BoP are usually operating in different markets, interacting with companies of different sizes and with different business models. Therefore having a clear view of the seller costs structure can be a daunting task.

  • Price volatility should be low.

This is true in certain markets where it’s easy to find a steady supply of bidders. However, overheated markets with several competing projects executed at the same time can create price volatility: basically, the resources that you need to build the wind farm (for instance the crane, or the mobile batching plant) will go to another project – another wind farm nearby, or possibly something totally different.

 Wind turbine foundations cracks – an update

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I already discussed in another post a frequent problem of with turbines foundation, the appearance of cracks.

In general, my impression is that the new foundations with anchor cages are much more reliable that the previous technical solution (the “embedded ring” – the industry standard some years ago).

However, every now and then I still hear story of foundations that need some kind of  intervention due to mistakes during design and/or execution.

Unfortunately there is a lot of secrecy on this issues. Unlike other civil engineering products (e.g. roads, dams, etc.) problems with wind turbines foundations are generally hidden, probably due to the fact that they are mainly private investments and probably the companies experiencing an expensive problem prefer to have as little publicity as possible.

From several studies I’ve been able to found on the topic it seems that towers and foundations are accountable for less than 5% of WTG failures – being blades, gearbox and generator much more frequent sources of problems.

However,  while replacing a blade or a gearbox is “business as usual”, replacing a foundation is not  really an option – and any intervention will probably be quite expensive.

Problems in the foundations usually materialize as cracks in the concrete.

In many cases they are caused by the cyclical nature of foundation loads – with a lifespan of 20 to 25 years the foundation can be exposed to millions of loads cycles.

These cracks can be radial or circumferential, and appear both in the pedestal (the visible part of the foundation, where the tower connect to the foundation) and in the buried part of the foundation.

Usually these cracks tend to appear soon (1 or 2 years) and they doesn’t pose a danger to the stability of the wind turbine. However, water could infiltrate them damaging the reinforcement bars.

The position of cracks can be defined with ultrasonic devices.

These technology use the echo of sonic waves to create tridimensional images of the foundation. In practice a crack will appear as a discontinuity, reflecting the wave to  the receiver.

Should cracks on a foundation worry you?

It depends.

It’s important to note that not all cracks are created the same: shrinkage cracks or cracks in the grouting due to an excess of material are usually less critical than the appearance of voids (for instance below the load spreading plate or the bottom flange of the anchor cage).