Piled foundation for wind turbines

I’ve noticed last week that the blog has no post on piled foundation and decided to write a couple of words on the topic on a flight back to Hamburg.

Piled foundations is a broad term that include several technical solution aimed at increasing the bearing capacity of the soil when design requirements such as bearing capacity, limited differential settlement and/or necessary rotational stiffness can’t be met designing a standard shallow foundation.

Piled foundation are a type of “deep foundation”, a concept opposed to the standard “shallow foundation” solution - other type of deep foundation solutions are for instance soil substitution and soil injections.

They are relatively frequent. The number of piled foundation that you will see are very dependent on the countries you are working in – probably almost 100% of the new WTGs in the Nederland are piled, while turbines installed in Portugal on the top of a mountain ridge are usually on a shallow foundation.

Piled foundation are usually expensive – as a rule of thumb, they can cost between 1.5 and 2.5 times the cost of a standard shallow foundation for the same turbine type.

The selection of a solution will  usually depend on 2 main criteria:

  1. Cost: unsurprisingly, the main concern is usually to limit the impact of special foundations on the project budget.
  2. Constructability: sometimes the “best” solution can’t be selected due for instance to a shortage of machinery (a problem more frequent that you might think, above all in good times of strong economic growth), environmental constraints or other potential impacts (for instance, some piles are hammered and they can induce vibration on other building and structures nearby).

The main categories of piles are

Precast piles: this solution use concrete (or more infrequently, steel) piles fabricated somewhere else. Piles are driven into the ground by a hammering machine that measure the resistance of the soil to each blow. They say that “a driven pile is a tested pile” – and if you are not reaching the needed capacity you can keep hammering the pile to a greater depth as they are modular. Precast piles are usually more expensive and as mentioned they generate noise and vibrations.

In situ piles: this type of piles are fabricated on the spot. Augercast piles, also known as continuous flight auger piles, are drilled by a machinery that first drill the hole to the requested depth and after, while retracting the auger, inject cement ground in the ground. After concrete reinforcement bars are inserted in the pile. Drilled piles are similar – first the hole is drilled, after the walls of the excavation are kept into place using a fluid like bentonite or a steel casing. After, as in the previous case, concrete is pumped and concrete bars are inserted in the hole. The last type are rammed aggregate piles (also called impact piers), where instead of concrete gravel is inserted in the hole and after hammered by the machine. By doing so a higher density is achieved for the  gravel and for the soil around it. This solution is specially effective in seismic areas, were concrete piles can be broken by earthquake.

The pictures above are coming from a wind farm I’ve worked at many, many years ago (I think it was called Zarzuela, with 22x V90 2MW… now the WTGs in the market are over 4 MW!).

The piles shown were done by a company called Rodio Kronsa.

If I remember correctly they were built pumping directly the concrete, without bentonite. The concrete was pumped from a central pipe, while in parallel the earth was extract by the rotatory driller (basically, a huge Archimedes' screw).

After, the reinforcement bars were inserted.

Where do I go from here? Careers path in the renewable industry.

This post is about my personal experience with possible careers path in the onshore wind industry - what are the easy and the not so easy movements. I believe that the main concepts would be applicable to similar industries, such as Solar or Offshore.

It’s applicable to medium and big size companies organized in a classic way (Engineering design the product - in my case a wind turbine, Sales & Tender Management sell it, Project Management build it).

I focused on the departments that are near to my professional experience – therefore I’m not keeping into consideration Service and all auxiliary departments (e.g. HHRR).

The most “natural” career path is upward: you start for instance as a (Junior) Project Manager, you become a Project Manager, Senior Project manager, maybe a Project Director (if this position exist in your company) and finally you land in a Head of Project management position.

What makes fun (and broaden your view of the company) is to have also “lateral” movements.

I believe that some are easier than other. For instance I know many Project Managers that become Tender Manager and vice versa, or engineers becoming Tender Manager. Somehow more rare is to see a Sales Manager becoming a Project Manager, or a Tender Manager becoming a Sales Manager.

It’s not impossible, I know a bunch of cases. However, Sales guy are usually a different class.

For instance I’ve never met an Engineer with a Sales background: I’m not saying that it’s impossible, but for sure is a less frequent (and more complicate) career move.

I tried to summarize visually the idea in the picture.

I also beleive that  moving “lateral and up” would make the change even more complicate.

For instance it would be complicate for Tender Manager to become a Senior Project Manager (or Project Director), but it would be much more complicate for a Project Manager to step into a Senior Sales Manager (or Sales Director) position.

Google: powered by wind

One interesting fact that you might not know is that the Big G (that is, Google) decided several years ago to power 100% of its activities using renewable energy.

They reached their objective in 2017: what is surprising is that they started only in 2010, with a wind farm in the USA. Basically the strategy is to close Power Purchase Agreements with developers, aiming at investing in “additional” production.

“Additional” means that they don’t want only to buy renewable energy: they want to add this MW to the grid, building new plants and lowering the carbon footprint.

Another interesting fact is that they buy renewable plants connected to the same grid were the data centres are.

For instance their very first PPA was for a 114 MW windfarm in Iowa, one of the states with a data centre, while their 72 MW wind project in Sweden (2013) was intended to  “feed” the data centre in Finland.

The next step is to sell power to the grid at the spot price. Here is where the magic happen: Google is willing to sell it at a loss in case the spot price is lower than the price indicated in the PPA. The idea is that they wanted to use their financial power to give developers a steady cash flow, assuming the risk of fluctuations in prices.

They also get the famous “renewable energy credits”, and they use them to offset  the carbon footprints of the data centres.

A legitimate question would be “Why don’t you buy directly the renewable energy credits?”. The position of Google, as mentioned before, is that they want to help developers to create more and more renewable energy plants. They believe that the best way to do it is to  use their deep pockets to make more projects reality - "bankability", the possibility to get the money to finance a project from a panel of bank, is usually one of the critical point that kills many developments.

The good news, at least for people like me in the wind business, is that the vast majority of the investments (>95%) are in wind farms. The same apply to other business giants following Google on the renewable path, such as Amazon, Microsoft and Facebook.