Having the pleasure of studying dozens of subcontractors offers each month I’ve already seen a huge number of disclaimers.

Some of them are reasonable, some of them can be removed (basically, giving a price tag to the subcontractor risk excluded by the disclaimer) but some are “deal breakers”.

Which are the disclaimers that I warmly suggest not to include in your turnkey contract?

Here you have my personal “top 3” list.

Disclaimers on the quantities when a project is available

Basically, the message here is “Give me the contract. Later we’ll discuss.”

It unloads a huge risk on your side (be sure that the quantities will increase, or when they decrease you want get savings).

Also, it’s against the philosophy of a real turnkey.

Finally, it means that they haven’t studied the project, otherwise they would know with a reasonable approximation the quantities.

Disclaimers on the percentage of rock when a geotechnical survey is available

What we’ve got here is a subcontractor that wants to win easily. Even in cases when there is geotechnical information (trial pits, boreholes, etc.) they want to reserve the right to increase the price if the percentage of rock that they have estimated is wrong.

Don’t accept this one if you’re providing enough information.

Disclaimers on the presence of quarry & landfills

I hate this too. Not only for the possible discussions about alleged extra costs: the problem here is that this disclaimers means that the subcontractor hasn’t studied enough the project and has no idea about where he may buy the material, or unload the earth he don’t need.

This post is a follow up of my other post on the blade lifter.

When I’ve been discussing about this solution with the other guy in the business 3 or 4 years ago, they told me it was something utopic, a “nice to have, but still a dream”.

Well, apparently now the blade lifter arrived, and it’s here to stay - and with a more aggressive configuration.

We’ve used it in a project in central America together with GES, a company specialized in wind and solar project, who bought one.

I’ve also discovered that another transport company in Italy (SIA – they are specialized in WTGs components transport) bought one in August 2014.

Clearly, this unlock the power of the blade lifter in Europe: I’m sure that in some complicated situations, it will make sense to move it from a country to the other.

There is a very good post on the company web describing this solution – have a look.

They’ve also done a very professional video (embedded in this post).

Resuming the key features:

 

  • Produced by Scheuerle
  • Maximum angle 60°
  • Maximum capacity is 25 tons
  • Maximum slope: 23% (paved road) / 18% (dirt road)
  • Wireless wheel remote control

 

Enjoy the video!

Having the opportunity of working at several project worldwide I already discovered that the idea of what is “cheap” or “expensive” may vary a lot depending on the country.

Also, huge countries like Brazil or Chile may show a relevant price dispersion depending on the area (Patagonia or Atacama desert?).

A third consideration is that, due to inflation, market situation, other project being constructed at the same time, etc. the prices may move a lot (downwards, but normally upwards) from one year to the following.

However, here you have my favorite top 5 of the most expensive price I’ve ever seen. They are totally crazy, even with all the above considerations.

 

Concrete: Mozambico (900€/m3)

Steel: Morocco (15€/Kg)

Embankment: Mexico (241€/m3)

Crushed stones base layer: Mozambique (450€/m3)

Overheads: Chile (50% of the project cost)

 

On the cheap side I'd like to mention Portugal: a country with a lot of skilled civil works companies, used to the renewable business - and with great food as well! ;-)

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Among the numerous fenomenous that follow a Pareto distribution (i.e., 80% of the effects come from 20% of the causes) there is the price of civil works in wind farms.

Through the years we’ve developed a really completed, exhaustive documentation for tenders. Our beautiful Bill of Quantities includes hundreds of items.

However, how many of them have a real impact on price?

Well, just 5.

Basically, around 70%-80% of the total price is driven by the following items:

  • Concrete
  • Steel
  • Cut
  • Fill
  • Crushed stones for base layer

I’m not saying that it would be a good idea to ask only these 5 prices to the subcontractors.

There are many reasons to produce a complete and accurate Bill of Quantities – for instance, to be sure that you are on the same page with the subcontractor.

Being a niche sector, often smaller local companies have an idea somehow distorted of what is included in a wind farm.

They might ignore the existence of something (“You need 50.000 kg of grout? For what?”) or overprice one or more items (20.000€ to assembly an anchor cage is a good example).

However, at the end of the day what will move the total price will be the 5 items listed above.

Concrete is usually the heaviest item. I’m including in it all types of concrete that might be found in a wind farm (lean concrete, foundation concrete, concrete used in roads, etc.).

Although obviously the numbers will vary depending on the project (a mountainous area with a lot of rock will have expensive earthworks, while a project with dozen of piled foundations will rise steeply steel and concrete price) I’ve seen that they can be used as a rule of thumb and are a useful guideline when I skim through the offers.

As I don’t know if it’s better to present a graphical example with a pie chart or bar diagram (and I’m trying to improve my Excel skill) I attach both.

It’s a 50 MW wind farm quoted by a subcontractor who charges a lot Overhead Costs (which is perfectly fine for me: I don’t want to have them “scattered” where they don’t belong).

71% of the total comes from the 5 key cost drivers.

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I’m currently having the pleasure of working at a wind farm project in Senegal.

One of the challenges I’m facing is the use of unconventional materials, at least based on my European background.

For instance, the internal roads and crane pads will be probably made of laterite, a solution very common in tropical climates successfully used in several countries for the subbase and base layers.

These days I’ve been investigating on the peculiarity and the technical requirements of this material.

As a starting point, I’ve selected the useful “Guide pratique de dimensionnement de chaussée pour les pais tropicaux”.

On page 36 you will find a catalogue of low traffic roads suggested cross sections. Considering the subgrade CBR of the wind farm site, I’ve selected 2 layers of 35 cm (foundation) + 15 cm (base), both made of laterite.

The granulometry can be found at page 60 (foundation) and page 73 (base).

There is also a requirement about the maximum increment of fine particle percentage (less than 8%), while the PI is greater than normal (<15).

Finally, you’ll also find that maximum CBR swelling is 1%.

The document “Characterisation of laterite for road construction”, from where I’ve stolen the graphs above, explains that compaction can greatly change the granulometric distribution of this material. Therefore, it is wise (although unusual) to ask for a granulometry check after compaction.

Another useful research is this “Review of Specifications for the Use of Laterite in Road Pavements”. The authors suggest using the Brazilian standards. You’ll also find an extended bibliography, a detailed analysis  of the criteria followed in several countries and “real world” results on existing roads in numerous countries.

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I’ve recently had the pleasure to be exposed recently to the FIDIC contracts structure. Therefore I want to share with you my impression regarding the possibility of using this type of contract in wind farm EPC tenders.

The first FIDIC contract was released in the fifties. After half a century, the FIDIC contract family is expanding over the years to match the necessity of the market.

As you probably are aware, the different types of contracts are commonly referred to with different colors (red, green, yellow, etc.) from their cover. For instance “red” is for construction (of projects designed by the Employer), and “green” is for small work (maybe less than 500.000 USD).

The three types more appropriate to my particular sector would be the red, yellow or silver book.

Although there is obviously much more, I will resume the main characteristics of each of these 3 contracts type in the following table. I’ve not included the other books because they are not applicable to the wind farm sector.

Parameter RED YELLOW SILVER
Design Employer Contractor Contractor carries the risks
Design Approval Engineer may approve changes or ask for variations Engineer approves or rejects before executions N.A.
Proposal Unit Prices Lump-sum Price Lump-sum Price
Payment Schedules Measured quantities Payment percentages Payment Calendar / Payment percentages
Engineer Yes Yes "Employer's representative"
Risk Distribution Employer carries design risks More Distributed Contractor carries the risks

So, which contract type makes sense in a wind farm EPC?

Let’s start to the easiest contract to discard: the silver book.

This typology of contract would be a full EPC where almost the full risk is suffered by the contractor. There is no engineering available, therefore quantities are estimated and risk such as subsoil quality must be included in the contractor price.

Obviously, this made the contract not operative for projects such as tunneling, wind farms or other “high geotechnical risk” activity.

Theoretically, it is possible to include in foundation price this risk. We even have done it in the past, for clients not willing (or not able) to pay even for a preliminary geotechnical survey. But the price of a piled foundation can be 2 times the price of a standard, shallow foundation. Therefore numbers become huge quickly, and this approach kills the majority of the projects.

Also, the client is not really willing to pay for something that it might never get (that is, major civil works). This basically eliminates the possibility to use the silver book, a contract that makes sense in situation where both party knows that little deviations are to be expected (maybe some type of plant).

These leave us with the yellow and red books.

In the red, engineering is made by Employer and payments are made on the basis of the real quantities executed. Employer carries the risk for contract amount increases: as you might guess, this point is not particularly welcome by banks or by companies such as Vestas.

In the yellow, Employer prepares only the «Employer’s Requirements», including Draft layout, Operational Parameters, Technical Specifications and Financial Proposal.

Tenderers submit their technical proposals together with their financial proposals, including at least methodology, basic design and drawings, bill of and similar supporting documents.

So maybe you think that finally we’ve found of dream contract, the FIDIC yellow book.

Well, no. The problem is that contractors are unwilling to give a real closed price: basically, construction companies don’t have an engineer department big enough to properly follow each tender and give a good price. Being a really specialized business, often you ask price to good local companies with no wind experience.

This lead to misunderstandings, unreasonably low or high prices and (even worst) discussion during execution, when you already have a closed price with your client and accept a reclamation of the subcontractor would go against contract margin.

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After a long search I’ve finally found a direct correlation between CBR and gravel thickness for unpaved gravel roads.

I’ve discovered that often wind farms are built in areas with a low (<5%) to very low CBR.

Somehow empirically, we’ve started with a standard 20 cm layer of gravel. We’ve learned the hard way that often this is not enough.

I’ve also seen that several competitors in their EPC projects opt for a double layer subbase+base with values such as 20 +20 cm, or even 30+20. Even if it may look expensive, this solution is probably cheaper on the long run, above all in wind farms in rainy areas and poor drainage where the road can be easily washed away.

I’ve also commented in another post why I think that national norm methods such as AASHTO are not applicable for wind farms (basically, because traffic is very low).

Therefore, I’ve been searching for a direct relationship between CBR, axle load and gravel thickness and I’ve found this:

According to the nomogram for instance with an axle load of 10 Tonnes and a CBR of 2%, you would need about 35 cm.

If you are based in Europe, you will probably want to use a more common value of 12 Tonnes axle loads.

The picture has been taken from a document made by Terram (a geotextile producer).

Please note that I don't know the source, but the numbers that it generates appears reasonable.

You can download it here.

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I’ve been recently asked to justify the roadbed thickness for a wind farm I’ve designed.

For several reasons (mainly because the majority of documents are redacted by non-civil engineers) the engineering companies supporting our customer ask for a written demonstration that the road design comply with the requirement of the famous AASTHO 1993 green book.

Unfortunately, it is not possible to use it for wind farms, and I’ll explain you why in this post.

As you will probably know, AASHTO defined an empirical equation  after a series of full scale test done about 50 years ago in the USA, the famous “Road test”.

This equation, very large and complicated indeed, gives as a result the “structural number” (SN) – a number that can be used to define the required roadbed thickness.

The formula looks very complicated, but the idea behind it it’s pretty easy: given the expected number of vehicle using the roads (defined as standard “equivalent single axis loads”) and other physical and project related variables you can define the correct thickness of the various materials selected for the road bed.

This is how the equation looks like:

Where

W18 = Predicted number of 80 kN (18,000 lb.) ESALs (equivalent single axis loads). Basically different type of vehicles (car, trucks, bikes, etc.) will use the road. To simplify the calculation, all this different axes are concerted to “standard axes”.

ZR = Standard normal deviate.

So = Combined standard error of the traffic prediction and performance prediction. Both ZR and So choice depend on the type of the road (for a major highway you will need more confidence in the result, while for a local road you can assume some risk).

SN =Structural Number (an index that is indicative of the total pavement thickness required).

Basically, each layer has a thickness (D) and a “layer coefficient” (a) representing the quality of the material.

In wind farm construction normally only one or two gravel layers are used.

Therefore the equation SN=a1D1 + a2D2m2 + a3D3m3+… will simplify becoming SN=a1D1

a1 = Layer coefficient. Gravel would be around 0.14

D1 = Layer thickness (inches).

ΔPSI = Difference between the initial design serviceability index, p0, and the design terminal serviceability index, pt. This concept is needed to incorporate in the equation the quality of the road at the beginning of the considered timeframe, p0 and the quality of the road at the end of the life span (pt).

MR = sub-grade resilient modulus (in psi). This number indicates the quality of the sub-grade.

Said that, let’s see why this beautiful and highly effective equation is of little (if any) utility for wind farm design.

Basically, a highway or an urban road is damaged by the recurring transit of heavy loads – that is, bus, trucks, etc. This trucks use the road for several years, causing accumulated damage.

What happens in a wind farm is that, when the WTGs are installed and producing, no one will use the internal roads – only a few service cars every now a then. The ESAL number will be almost zero.

What normally damage wind farms internal roads without heavy traffic is poor drainage, incorrect roadbed material selection or poor construction (e.g. incorrect compaction), not cyclical mechanical loads above the elastic limits.

Therefore we normally design the roadbed based on the CBR value: we know that with a very good CBR in dry climates 20 cm are normally enough, while for low to very low CBR (>5) we use 40 to 50 cm.

Below CBR=3% special solutions are normally needed.

Here you have some interesting pictures that we’ve received trying to define the meteorological tower (also known as “met mast”) foundation for one of our wind farms.

Strangely, our customer is going to use a wired met mast for both towers (the permanent mast of the wind farm and the temporary mast used to calibrate the power curve).

As you can see from the pictures the mast has an interesting hinged base joined to the foundation of the WTG with 4 screws - looks like an effective technique.

The mast is tower model is KT470 from Kintech engineering.

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