About Francesco Miceli

Hello! My name is Francesco and I'm a civil engineer specialized in EPC (that is, "turnkey") wind farms projects. I'm currently based in Hamburg, Germany and I'm developing several interesting project all around the world - southern Europe, LATAM and various other countries. If you want to contact me please don't leave a comment in the blog (I don't check them very often) - you can use the contact form. You can write me in English, Spanish and Italian. To find a (somewhat concise) description of my non-wind business activities you can visit my webpage - www.francescomiceli.com If you want to know more about my work, here you can download my CV - www.windfarmbop.com/CV_Francesco_Miceli.pdf Hope you like the blog! Francesco

Lightning protection of wind turbine blades

Image copyright of Elsevier & X.Bian. Published on “Numerical analysis of lightning attachment to wind turbine blade”

I have received a question from a reader regarding blades damaged by lightning.

Specifically, the blade has been damaged before commissioning.

At first sight the consequences could be less significant than usual, above all if the main crane is still on site and there is a set of spare blades available as happens frequently in big wind farms.

I would also guess that the turbine supplier will have to absorb the cost unless the risk was already transferred to the customer.

I would also like to elaborate a bit more on the topic as lightning is a frequent cause of damage to wind turbines (specifically to the blades, as they are hit in around 75% of the cases).

Lightning are created by the electric field between the bottom of the clouds (negative) and the ground (positive).

The potential difference is significant (some MV). However, due to the distance, the average electric field is weak.

As the electrical charges at the bottom of the clouds accumulate a “downward leader” (a channel permitting the flow of negative charges) start moving toward the ground.

If this stepped leader is somewhere nearby a wind turbine (or another similar structure) the second phase of the phenomenon may start: an “upward leader” from the blade connecting with the downward leader and closing the circuit.

This is the instant where the “return stroke” start and you usually see the majority of the light.

Coming back to the blades the standard technical solution consist in embedding a copper receptor connected to the ground at approximately 1 meter to the tip. This receptor has a diameter of at least 50 mm (pretty much like the copper cable used in the earthing of the foundations).

The problem is that this solution doesn't works always: sometimes the lightning hit another point of the blade. Even if the surface of the blade is supposedly non conductive it has been observed that, due to the presence of pollution and water, it can behave like a conductor.

RUTE precast modular wind turbine foundation

Some days ago I have been contacted by Doug Krause, founder of RUTE - a green start up proposing an interesting solution for the wind turbine foundation.

Taking inspiration from the technology used in bridge construction RUTE is proposing a system of post-tensioned beams connected to a central hub. Each beam has an anchor system connecting it to the soil, and the foundation is delivered to the wind farms in around 20 elements.

Among the benefit the fact that the system is modular, less prone to quality problems (it is manufactured in specialized plants) and, at least in principle, reusable after 20 to 30 years for a new foundation: the lifetime of the components is over 40 years.

Decommissioning is also probably easier with such structure, at least compared with a standard shallow foundation.

Installation times can be cut as well – as it is delivered hardened it is ready for installation in few days from the start of the works.

I had a look at the technical specifications and I have seen that the bottom of the excavation is at the same depth of the standard solution, so no savings here. I have also noticed that in some situation soil substitution could be needed.

I have seen in their website that there is already a full-scale prototype built, so it’s much more than a concept. It has been installed at the Palmers Creek Wind Farm (Minnesota) on a 2.5 MW GE turbine with a 90 meter hub height.

Addenda (10 June 2019): I've received an email from the founder of the company. I post it here for the benefit of all readers.

Thank you Francesco for noticing RUTE.
That's a picture of our rock anchor, bulb T girder, model TG. The one we built in Minnesota is a box girder style, BX Foundation. It behaves just like an inverted T, spread foundation.

RUTE's biggest value to the BOP contractor is time. So most of the foundation works can happen off the project books and schedule. So a project can close finance and be erecting towers the same month. We'll hope to prove that claim this year.

Apart from the main BOP driver, the facility owner can run a pro forma out 30 years, or 40 years, the normal term of the land lease. And in those cases a foundation with bridge design, like ours, lasts well past 40 years. That's just a function of the post-tensioning which keeps the concrete in permanent compression. So there's an order of magnitude less fatigue damage than conventional reinforced concrete.

I can share some pictures from inside the foundation. You can walk around inside it and inspect.

Best Regards,
Doug, RUTE

Wind farm optimization algorithms

I have always been amazed by the number of published papers, master thesis and documents focusing on the use of algorithms to optimize the layout of a wind farm. Some of them were proposed more than 25 years ago, showing a continuous, sustained interest in the topic.

I guess that the reason for such abundance is the stimulating difficulty of the problem and the fact that there are huge investments behind a wind farm.

From a mathematical perspective the problem is complex due to the type of variables involved, both discrete (you can have 30 or 31 turbine but not 30.5) and continuous (for instance, the length of cables). Additionally there are strong links between variables (for instance higher turbines = higher tower and foundation cost) so finding the “sweet spot” that maximize earnings is not a simple task.

Generally speaking, these algorithm try to maximize the profitability of the investment, usually expressed in terms of Net Present Value (NPV). Basically they compare the value of all expenditures during the life of the project “in today money” with all the earning “in today money” using a certain discount rate for cash flows in the future.

Expenses belong to two categories, capital expenses (CAPEX) and operational expenses (OPEX), while net earnings are function of the amount of power produced, the price of electricity and the electrical losses.

Therefore even a simplified model should try to minimize these expenses:

  • Wind turbine
    • Model (power curve)
    • Tower
    • Installation
  • Civil works
    • Foundations
    • Roads
  • Electrical works
    • MV cables
    • Substation
  • Operation & Maintenance

While maximizing the production, a mainly a function of:

  • Wind
  • Wind shear (of the speed of the wind increase with height)
  • Wake effect (how turbine interact with each other creating turbulences)

The interaction between all these variables is what makes the problem interesting.

To give a few examples,

  1. Packing the turbines densely in a small area will lower the cost of roads and cables but will create huge production losses due to the turbulences inducted by the turbines upwind.
  2. Using a higher tower should increase the production – unless the wind shear is low, in which case the additional tower and installation costs would off weight the benefits
  3. A certain position could be extremely productive – but it could be very far away from the substation (increasing the electrical losses ) or on the top of a steep hill (increasing the earthworks cost)

Additionally you have to decide the level of complexity of the model. For instance the foundation cost can be considered as:

  • A lump sum, equal for all turbine models. Under such assumption, you would see a benefit decreasing the number of turbines but not switching to a different WTG model.
  • A function if the wind turbine model (greater loads = greater foundation).
  • A function of wind turbine model, geotechnical parameters of the soil and unit cost of concrete of still. This latter option, although more precise, would probably make the model very difficult to handle.

I believe that a reasonable compromise between complexity of the model and quality of the result can be achieved using nested algorithms as proposed by these researchers.

In the first steps, only the variables related to the turbines (power curve, wind resource, availability and cost) are considered. Once the turbine model and the layout are fixed the civil and electrical works can be considered, defining the optimum position of the substation (to minimize cable length) and the shortest roads connecting the wind turbines.

How much does it cost a wind turbine?

Onshore wind turbines - price per MW (Millions Euro)

The easy answer to this question is “Today it costs less then yesterday. And probably tomorrow it will cost less than today”.

Today (April 2019) the average price is around 700.000€ per MW – that is, expect to pay around 3 ML€ for a 4 MW wind turbine. That’s a huge reduction when you consider that some years ago the easy to remember formula was 1MW = 1ML€

If you are working in the wind industry you are probably aware of the huge pressure on wind turbine prices, driven by several factors and resulting in turbines cheaper than ever.

It is interesting to observe that, in the current market condition where wind turbines are very cheap, the majority of the main wind turbine manufacturers are reporting very solid order intake figures. However, net profit is still elusive and EBIT margin are very low.

For instance, Vestas reported 9.5% for 2018 while Siemens/Gamesa 7.6% (pre PPA and I&R costs) for the same period, with a guiding range for 2019 between 7% and 8.5%.

It looks like manufacturers are having more luck in the maintenance side of the business: margins there are significantly better.

One of the consequences of this situation is that several players are leaving the market (Senvion declared bankruptcy some weeks ago) and the consolidation of the sector continue: there are rumours about a possible purchase of Suzlon (heavily indebted) by Vestas, while Enercon absorbed the Dutch manufacturer Lagerwey some time ago.

In case you are wondering about the origin of the figures in this post I’ve taken the numbers for this post from the official annual statements of Siemens/Gamesa and Vestas and not from my friends working there 😉

Wood towers for wind turbines

I always believed that wood towers for wind turbines were a solution possible only in small, domestic WTGs (somewhere around 10 kW to maybe maximum 100 kW). There are several example available, for instance this product of InnoVentum.

Well, I was wrong: I see that some years ago (2012) a Vensys 77 1,5 MW turbine has been installed on a 100 meters tower. That is quite a number: a 77 meters rotor is considered small for today standard, however it fully qualify as a “utility scale” solution.

This full scale prototype followed a 25 meters test tower built by the same companies some years before.

Developed by 2 German companies (TimberTower & TiComTec) it has been built near Hannover. The foundation is standard (concrete) and the connection between the tower and the foundation is made trough 4 meters long steel rods.

With a somehow unusual octagonal cross section the tower diameter is comparable to a standard concrete or steel solution. I see however that other geometries are possible (hexagonal or dodecagonal).

The life span of this solution looks similar to the steel alternative (20 years). Unfortunately I haven’t been able to find information regarding the cost. For the sake of clarity it is not 100% wood – few steel elements are used inside the tower.

 

Wind farm project management: PRICE2 vs PMP

In another post I have discussed my experience with the PMP certification and its (somehow weak) relationship with wind farm project management.

In a nutshell, several processes and concepts are not directly applicable given the peculiarity of our industry. Said that, I believe that the PMP has a value, because it explain in detail a lot of tools and ideas that are used daily – for instance dependency types in Gantt charts, how to handle risk management or the “stakeholder management” concept.

Some days ago I have made another PM certification, the British de facto standard PRINCE2. The main reason for that has been my curiosity to see another point of view on a very broad topic such as project management.

Both certifications are trying to live together and differentiate themselves:

  • PMP define itself as a “standard” and comes with a mountain of processes and techniques.
  • PRINCE2 define itself as a “methodology”, coming with models and templates but very few techniques.

My personal impression is that the role of the Project Manager in PRICE2 is less relevant compared to the PMP idea of the same role – basically he has some decision margins, but he’s somehow squeezed between the Project Board making the big decisions and the teams doing the actual job. As soon as one of the tolerance levels is exceeded, he need to escalate the problem to the Project Board (that in the wind industry, if it exist, is usually called “Steering Committee” or something similar).

This image is strikingly different from the one that my mentor Luis Miguel gave me when he told me that, in the infancy of the wind industry, the PM was basically “the God of construction site”. Possibly the image is a bit strong but it makes the concept crystal clear.

Said that I also had the feeling that PRINCE2 was much easier to follow in the definition of the workflow, with less processes (seven) clearly linked between them and few key concepts (“Themes” and “Principles”). Understanding the relationship between the 49 processes of PMP is not that easy: I had to print them in a huge A0 and spend a lot of time staring at it to make a sense of them.

An interesting argument that I want to mention against PRINCE2 is that it is “unfalsifiable”, in the scientific sense defined by Karl Popper. This basically means that PRINCE2 has to be tailored (that is, adapted) to the specific project to work properly. If something goes wrong, you cannot proof that the problem is PRINCE2 (because possibly the tailoring you have made was wrong).

In conclusion I would recommend both certification to people interested in knowing more about project management, even if some tools, techniques and processes are not used in wind farms construction.

Concrete tower assembly in Chile

 

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.

Long term instrumented monitoring of wind turbine foundations cracks evolution

Fiber Bragg grating sensors (Image copyright fbgs.com)

Some weeks ago I have discovered that, as I am currently enrolled as a university student (getting “slowly but steady” a second degree in Economics) I have full access to the Elsevier database.

This is an enormous amount of information, including all the best scientific papers and technical articles published by industry journals.

I am using this possibility to learn more and stay updated on several niche topics that I found interesting – from recycling of wind turbine to bird strikes to foundations pathologies.

Browsing the database, I recently stumbled upon an interesting article published by Jack McAlorum et al. from the University of Strathclyde (Glasgow).

The paper is called “Deterioration of cracks in onshore wind turbine foundation”.

The authors instrumented an octagonal slab foundation (sometimes called “star foundation” or “wall foundation”) to monitor the evolution of existing cracks.

I already wrote a couple of posts on foundation cracks: they can be due to a variety of root causes, such as:

  • Design mistakes
  • Errors in the composition of concrete mix
  • Extreme temperatures
  • Errors in the execution of the wind turbine (for instance, concrete poured in different batches creating construction joints)
  • Failures due to the use of an embedded can (this is a frequent failure reason for older wind turbines)

The paper does not specify the reason for the cracks. However, as typical, the most severe cracks were in the side of the wind turbine facing the wind (as the concrete is in tension there).

What it is interesting is the fact that the behaviour of the foundation has been monitored for a very long period (over 9 months) and under standard operating conditions. This is very unusual: while other key component of the turbine like the gearbox are constantly monitored and the data is collected trying to detect problems and predict failures, I have never heard of such monitoring for the foundation.

Additionally it is interesting the type of sensor used: instead of standard accelerometers or strain gauges the researchers used a strain sensor based on fibre-optic called “fibre Bragg gratings” (FBGs).

Basically it is a sort section of optical fiber treated in a way that some specific wavelengths are reflected and some are transmitted. They can be used as a strain sensor because when they are deformed the transmitted and reflected wavelengths shift, allowing a calculation of deformation.

Cracks can evolve with 3 different displacement type:

  1. Opening (the crack becomes wider)
  2. Sliding (one face of the crack slides on top of the other)
  3. Tearing

Through the monitoring period no significant evolution of cracks was observed. Basically, the wind turbine owner was lucky: cracks did not deteriorate and no intervention was needed.

Unfortunately, the cost associated with the monitoring are not shared, so it is difficult to make a business case (cost of immediately repairing the cracks with grouts or epoxy resins vs. cost of monitoring to see if the intervention is needed).

I also see that this solution only allow monitoring visible cracks. This is a strong limitation, as several failures originate in a non-visible area of the foundation.

Said that the idea is certainly interesting and useful, above all considering that some turbine are kept in operation for a very long time, even exceeding the design life of the foundation (usually 20 years).

 

Over and over and over again: serial defect clause

The serial defect clause is a warranty frequently requested by customers.

It belongs to a classic “tryptic” of warranties allocating risk on the turbine suppliers:

  • General warranty, for defect in design, manufacturing, installation, etc.
  • Power curve warranty
  • Serial defect warranty

Generally speaking, a serial defect is a component defective on a significant number of turbines. If there is a certain percentage of defective components, the warranty force the turbine seller to replace it on all the turbines.

As you will imagine, the tricky part is the specific definition of the clause.

Among the key point to be defined these are specially important:

  1. The definition of defect / defective.
  2. The time-frame for the defect to appear. How many years?
  3. The reason for the defect. Is the root cause the same? You can have for instance many blade failures caused by different problems.
  4. The percentage of failures needed to declare a serial defect. Is it 10%, 20%, more?
  5. The population of turbines used to calculate the percentage of failure. Only the wind turbine in the wind farm, all the turbines of the same model owned by the customer, all existing turbines of the same model?
  6. Who should confirm the existence of the defect. A reasonable compromise for this point can be an independent third party.

The reason behind this clause is that such serial defects happened in the past - not only in the infancy of the wind industry, but also in more recent years when components have been replaced on massive numbers of turbines, even of Tier 1 manufacturers.

Without this clause the buyer can be left in a very uncomfortable situation where maybe he is aware of the (latent) problem but only if the components that fail during the Warranty or Service period are replaced.

Transfer of title & transfer of risk

Transfer of title and transfer of risk are 2 key concepts in wind farms contracts (and, presumably, in many other comparable businesses). They appear in both EPC and Supply Only agreements.

This is what they usually means:

Transfer of title (ToT): the ownership (of the entire turbine or of one of the component of the wind farm, such as the foundation) is transferred to the buyer.

Transfer of risk (ToR): risk of damages and losses is transferred to the buyer.

Although it may look counterintuitive they do not have to happen at the same point in time: for instance, an EPC contract could have transfer of title when a certain percentage of the wind turbine is paid -for instance, 80%- and transfer of risk only after commissioning (that is, the turbine is installed, tested and ready for production).

When the relevant percentage is paid is defined in the projects cash flow. In general, it could happen that the transfer of title happen many months before wind turbine installation.

The percentage of the wind turbine price to be paid to have transfer of title is usually one of the key negotiation topics. For the sake of clarity, the wind turbine seller would retain some case of security (e.g. a bank bond) until the equipment is paid in full in case the buyer stop the payments after the transfer of title.

It is worth to notice that one party (or both) might be interested in an early ToT or ToR, for instance if they are linked to revenue recognition. For instance, in some Supply Only or Supply and Install contracts revenue recognition is at ToR, so the turbine seller want to have it as soon as possible.

For a variety of reasons, it could be the buyer interested in an early ToT or ToR, possibly even before the completion of the wind farm balance of plant (basically, when the wind farm is not ready for installation). In a similar scenario the turbines would be delivered to a temporary storage area where the ToT and ToR would happen.

One more interesting point is that, in some jurisdictions, a sales tax could become applicable when the ownership of the turbines is transferred. This could be a good reason for an early or late transfer of title in a different jurisdiction.