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

Wind turbine blade damage detection systems

Wind turbine blades damages. B.F. Sørensen, E. Jørgensen, C.P. Debel, H.M. Jensen, T.K. Jacobsen, K. Halling, et al., Improved design of large wind turbine blade of fibre composites based on studies of scale effects (phase 1). summary report.

Wind turbine blades are rarely subject to catastrophic failures, although you can find a bunch of videos on YouTube with blades flying away or falling into pieces.

They are however subject to several problems, such as cracks, debonding of the various layers, internal delamination, etc.

As an order of magnitude blade failures are accountable for approximately one fifth of the problems usually seen during the operational life of the wind farm.

Such problems have a direct impact on the profitability of the plant and can be extremely expensive to fix.

Some issues can be fixed leaving the blade attached to the rotor. However not all problems can be solved without dismantling the blade, and the fee associated with the cranes needed for the dismantling can be very high.

In the worst case scenario a blade substitution will be needed, and the transportation cost will add up.

A certain number of failure is attributable to design error (insufficient material strength under fatigue or extreme loads) or manufacturing problems.

However the overwhelming majority of issues seem to be attributable to extreme weather – basically strong winds, thunderstorm (including lightning strikes), ice, pollutants, etc.

The effect of ice accumulation is especially dangerous in case of asymmetrical accumulation, because it can create unbalanced loads in the rotor.

Pollutants, usually in the form of airborne particles (e.g. sand) can shorten the life of the blades accelerating the erosion of the superficial layer. A gel coat usually cover the outside of the blade to protect it from ultraviolet degradation, water, etc.

Therefore the erosion of the external layer may have two impacts: lower the efficiency of the blade (this will have a direct impact on energy production, and ultimately on money) and accelerating the degradation of the blade.

Some areas of the blades are more prone to damage: tip, root and joints accumulate the majority of reported damages. The distribution of failures has however a typical pattern: erosion is more frequent in the tip side (due to the higher local speed) while cracks are more frequent toward the root.

Blades crack and erosion regions. Zhang, H., 2016. Reducing Uncertainty in Wind Turbine Blade Health Inspection with Image Processing Techniques. Iowa State University, Ames, Iowa

A variety of methods has been developed to detect and monitor damage. There is a consensus on the fact that early detection of a problem mean usually lower maintenance costs.

The “perfect”, ideal method should be able to assess the full scale of the blade without contact, allowing for continuous remote monitoring.

Unfortunately such methods does not exist yet. Among the most promising techniques it is worth mentioning:

The use of strain sensors, either embedded in the blade or on the surface. It is the same type of fibre-optic called “fibre Bragg gratings” (FBGs) that I have described in another post. As each sensor measure only direct strain and shear strain only in one point of the blades many sensors will be needed to have the full picture. Another problem is that the sensor can give a "false positive" result if it fails due to creep, fatigue, etc.

Measuring the acoustic emissions of the blade is another extremely interesting method to find damages. Unfortunately it is a complex system that need many sensors and physical contact with the blade of many sensors – something that could be difficult to achieve in operational wind farms. Sensors operate on an extended frequency range (50 kHz to 1 MHz) and as in the case of the strain sensor are used not only for the blades but also for the other components (gearbox, bearings, etc.)

Ultrasound is an extremely common non-destructive technique, that basically analyse the ultrasound waves reflected by the different layers of materials and by discontinuities in the materials. The main problem of ultrasound detection is that usually physical surface contact is needed. On top of that, there is also usually time consuming (and it can be hard to process the signal). It can however be extremely useful for an in depth analysis of the situation of the blade.

Thermography is a technique that use infrared cameras to assess the temperature distribution. If there is a defect in the structure the flow of the heat will be disrupted, causing temperature gradients. Thermography comes in two types, passive (made from the ground using the “natural” temperature) and active (heating the surface).

The last method, and possibly one of the most promising giving the quick evolution of computer computational power, is Machine Vision. One or more cameras are used to capture images of the blades subsequently analysed with image processing algorithms.

There are several interesting studies on machine learning – basically using two set of image, one of blades with known failures and the other of blades without problems, to “train” the algorithm to detect issues.

 

 

How good is the wind farm you are working at? Some indicators

So, how good is the wind farm you are working at?

There are several parameters that can be used to assess a renewable energy project and to compare different projects.

Among the most used, it is worth mentioning the Capacity Factor, NPV, IRR and LCOE.

Capacity Factor is the ratio between the actual energy production of the wind farm (that is, GWh/year) compared with the theoretical production.

Expressed as a percentage it is usually a number somewhere between 20% and 50%. Wind farm with a capacity factor above 50% are usually regarded as quite exceptional.

It is basically function of two parameters, wind variability and wind turbine selected for the project. On top of that you will have several losses - for instance electrical losses, noise curtailment, wake losses, etc.

To calculate it you will simply divide the energy produced by the wind farm by the nameplate capacity by the number of hours. Due to the seasonal variability of the wind it makes sense to make an yearly calculation.

What is interesting is that Capacity Factor is fundamentally and economical decision. At the end of the day you want to improve your business case, so it could make sense to install wind turbines giving a lower capacity factor (but with an even lower total cost).

The Net Present Value (NPV) is today’s value of a future cash flow.

In the formula C is the cash flow (-C0 is the initial investment, C1 is the cash flow of the first year and so on until the last year, n) and r is the discount rate.

This metrics give priority to the absolute return of the investment. Basically it is useful if you have only one shot: if you put all your money in a single project you will prefer (ceteris paribus) the one bringing more money.

The discount rate reflect the fact that money in the future is worth less than money today – for inflation, cost of opportunity, etc.

Internal Rate of Return (IRR) is the discount rate that makes NPV = 0.

This metrics give priority to the percentage return. It could be useful for instance if you can pick several projects among many.

Levelized Cost of Energy (LCOE) is defined as (CAPEX + OPEX ) / AEP

CAPEX (Capital Expenditure) is the money that the wind farm developer will have to put in all the assets – not only the wind turbine itself but also the infrastructure (roads, foundations, substation, etc.), and the development costs (everything from land lease agreements to the engineering studies).

OPEX (Operational Expenditure) is what the wind farm owner will spend to have the wind farm up and running.

This include basically the maintenance of the wind turbines (they need new oil every now and then, pretty much like your car) and of the substation equipment. As the lifetime of such project is increasing from what used to be industry standard (20 years) to 25, 30 years and more.

Additionally the more the wind turbine gets older the more is likely that it would need major maintenance (for instance a new gear box).

LCOE makes a lot of sense when you are trying to compare energy produced by different technologies, for instance wind and solar photovoltaic.

Lazard (a huge private investment bank and financial advisory firm) distribute periodically a study on the evolution of LCOE. Currently available in version 13 it gives you some visibility on how much different forms of energy cost without subsidies.

I still remember when I started working in the renewables sectors about 10 years ago. Comparing the cost of solar and wind I believed that my colleagues who decided to work in solar were crazy as the cost per MWh of Solar PV was huge.

Well, it looks like I was wrong.

What do you call it? Basic terminology in wind farm construction

Lately I have found several high quality videos on YouTube with time lapses of wind farms constructions.

I have decided to take some screenshots and use them to create a very basic BoP visual dictionary. You can click on the pictures to make them bigger.

Enjoy!

Crane and auxiliary crane lifting a steel tower section:

A rotor fully assembled on the ground before erection. It start to be an outdated practice due to current rotors size and weight:

The different areas of a crane pad in a wind farm in Australia (Goldwind's Cattle Hill):

Main crawler crane and its elements:

A blade lifted by an auxiliary crane. One of the workers is under a suspended load - not a best practice:

Workers completing the anchor cage assembly:

Slingers & trenching machines in wind farms: a guest post by Christopher James

After posting this article on Slingers I have been contacted by Christopher James, an expert on the topic with an exceptional amount of real world experience.

He has been so kind to share is knowledge on the theme and I am thankful for that. I am sharing it with you in the very comprehensive post below with almost with no edits.

You can reach him via LinkedIn or following one of these links:

https://slingers.com

http://buckeyetrenchers.com

(Beginning of guest post)

This video link shows some of the applications of the Slingers working on wind farms.

Slingers are high speed material placing machines.  By introducing them to backfill cable trenches most companies can remove one piece of earthmoving equipment, one operator and two or more labourers.

While doing all of this they are able to increase production of over 10 times faster than some operations and while almost reducing waste of the imported material.  In the  video below these speeds of backfilling are real time speeds.  The machine was backfilling cable trenches on a wind farm in NSW, Australia.

 

Speed is obviously an advantage but it is the ancillary savings like reduced labour and equipment.  Also the waste of the imported material is huge with traditional methods.  In some cases on large scale wind farms we are able to off-set the cost of a Slinger to just the savings alone…all on one job.

These machines can move up to 3.5 cubic meters per minute.  This is in a perfect world and perfect conditions.  Generally speaking a good average to work on is 8 to 10 meters per minute on most 400mm wide trenches.  As you can probably tell this is huge production compared with some of the old methods.

This wind farm in NSW where we brought this TR-30 Slinger (rubber tracked with cab) they were using a 25 tonne articulated dump truck and a 20 tonne excavator.  The excavator would scoop material out of the truck and place into the trench.  We were around 15 times faster than this operation with the obvious one less machine and operator.

I have also added the below the link to a video by Buckeye Trenchers working on the cable trenches on wind farms in the USA.  We are agents for Buckeye Trenchers and these really are high speed trenching machines.  A Bucketwheel trencher is suited to soils or small stoney ground.  They are not suited to rock at all.  Once you hit rock you have 2 options, either a Chain Trencher or a Rock Wheel trencher.  Either way there are options.

A chain trencher is one of the most common trenchers around the world, as seen in the Vermeer video link below.  These units can range in trenching widths from 300mm up to over 2 meters wide.  Ranging in weight from 20 tonne up to over 200 tonne.

A rock wheel trencher as shown in the video below by Vermeer will generally only go up to 350mm wide trench.  Now I have seen up to 450mm wide but not a very common machine.

Next you step up into the “dig, lay, bury” machines.

Rivard make a unit in the attached video. These are great units for single pass operation.  From experience though if one link in the chain stops, like the trencher or the cable spooling and so on, everything stops.  This can be quite costly.

From my experience having crews working on multiple fronts at once limit your risk and usually allows for a more productive environment.  For example a bucketwheel trencher should get around 3 kilometres of trench done in a shift, the same goes for backfilling with a Slinger (depending on many factors).

If you were doing a single pass operation you would not achieve numbers like this.

It really comes down to how much production you really want, or you can achieve.

Each operation has its pluses and minuses, no doubt about it.  As I was always taught in pipelines, get the basics right.  Get the equipment right.  Lower your risk as much as possible and then find minutes to shave off each process.  Laying cables is as repetitive as it comes, just like pipelines and it is all about streamlining processes as much as possible to get as efficient as possible.

This is why we have always used trenching machines for pipeline works.  They replace many excavators (bucketwheel trencher can replace up to 10 x 25 tonne excavators).  Trenchers also make exceptional backfilling material, excavators just cannot do this.

As a general rule (very general as all ground conditions change dramatically) please see the below for trenching equipment production:

  • Bucketwheel in good, dry soil ground conditions: 3 kilometers up day digging 400mm wide trench at 1.5 meters deep
  • Chain trencher in firm, dry, small stone ground conditions: 800 meters to 1000 meters per day digging 460mm wide and 1.5 meters deep with a 45 tonne class machine

I cannot give production in rock as it is too much of an unknown with the hardness and so on.

I have had 45 tonne class chain trenchers take 3 days to cut 4.5 meters of pink quartz and then dig 600 meters of hard limestone. It is too much of a variant to give some solid figures.

Additional links that you might find useful:

https://www.linkedin.com/pulse/where-how-use-my-slinger-episode-10-wind-farm-christopher-james/

https://www.linkedin.com/pulse/7-reasons-why-bucketwheel-trenchers-bring-efficiency-your-james/

https://www.linkedin.com/pulse/where-how-use-my-slinger-episode-2-trench-backfill-imported-james/

https://www.linkedin.com/pulse/stop-wasting-money-when-backfilling-your-trenches-imported-james/

Can a rotor be smart? Passive optimization systems

The spectacular growth of the dimension of the wind turbine has led to the introduction of several interesting technical solutions. Different type of towers (concrete, hybrid, lattice, self-erecting, etc.) and new technical solutions for the foundations appeared in the last decade, trying to have the lowest possible cost of energy.

The rotor of the turbine has followed the same trend. With the impressive size of the blades currently in the market (today we are around 70 meters, the width of a football field) it is not surprising to see a variety of new concepts already in the market or under development.

One of the key issues of very long blades is that it is difficult to optimize them: finding the “sweet spot” for a component exposed to a variety of wind flow characteristics during its operational life is not easy, above all if such characteristics are not uniform along the blade.

The engineers designing the blades are trying to achieve several goals, such as:

  • Increase the energy production (maximizing the aerodynamic efficiency and the power extracted from the wind)
  • Reduce the loads on the structure
  • Create a solution that can easily be transported on public roads and installed with cranes already in the market
  • Extend the life of the blades (we are moving to the 25 or even 30 years mark)

All these objectives should be reached with the lowest possible cost.

The term “smart rotor” refer to a variety of technical solutions whose purpose is to increase the production or reduce the loads.

They belong to two categories, passive systems (not controlled by a software or an operator) and active systems.

Among the passive systems the most interesting are:

Vortex generators. Believe it or not, you can buy the elements generating the vortex from 3M (the same company that invented the Post It all around my desk). You can use them to retrofit pitch-regulated turbines sticking them near the root of the blade, where the air flow is separated by the blade (that is, it is “stalled”).

They basically work reducing the separation of the flow, increasing the production 1 or 2 percentage points (they can be a lot of money).

A second passive technology is the bend-twist coupling.

As you will guess from the name it creates a link between the bend and the twist of the blade, with the object to reduce fatigue loads created by sudden inflow changes during turbulent wind conditions.  

The wind blowing on the blade is creating 2 forces – “lift” (the one pulling up the blade and making the rotor turn) and “drag” (the one bending the blade backwards). As a general rule the engineers try to minimize the drag and maximize the lift, achieving a high “lift to drag” ratio.

With the bend-twist coupling the loads are reduced because the blades “adapt” its shape changing its shape and the angle of attach when deflected.

This coupling can be achieved changing the geometry of the blade (geometric coupling) or by changing the direction of the fibre inside the composite material (resin + fiber) that constitute the blade.

This interesting technology is currently being investigating by several entities, including a heavy weight such as the Fraunhofer Institute for Wind Energy Systems.

Image Copyright Mark Capellaro, 2012 Sandia Wind Turbine Blades Workshop

I also described some months ago the serrations. They have a different scope (reduce the noise) but I believe they can be consider a type of passive optimization system.

A mind map for BoP

Yesterday while I was traveling to meet my family in Italy I started thinking at how a mind map for the BoP would look like. Luckily the train had a free internet connection and I have found a bunch of website helping you to create a mind map online (for this particular exercise I have used Mindmup).

I was able to draw only the first nodes because I was travelling with the kids and they were unstoppable (and overwhelming noisy). I will try to expand it during the next weeks.

If you want to see the BoP mind map bigger click here.

Vortex bladeless wind turbines

I have always seen the wind induced vortexes as a problem – they create vibrations in the tower, that in some cases can start to resonate with the eigenfrequencies (the natural frequencies of the structure) and in the most extreme cases even collapse.

The existence of such vibrations is one of the reasons why it looks like that steel towers for wind turbine have reached their maximum height. At around 100 – 120 meters they start needing dampers and other anti-vortex solutions during installation and for the operational life.

What I was not aware of is that there is a Spanish start-up trying to develop a “bladeless turbine” which exploits this phenomenon to produce electricity.

I have some doubts on the idea of a “bladeless turbine” (I suspect that a wind turbine has, by definition, a rotating part). However the concept developed by the folks at Vortex is for sure very interesting.

The Vortex Tacoma (this is the name of the industrial version under development) is expected to have a height around 3 meters, a weight around 15 Kg and a rated power output of about100w.

Currently smaller scale prototypes are available and the target date for launch of the full scale production is end of 2020.

It looks like a big cylinder oscillating when the wind blow. I also see that they selected the same combination of materials as wind turbines blades (resins reinforced with carbon fiber and/or glass fiber), while for the bottom section anchored to the ground they have selected a carbon fiber reinforced polymer due to its resistance of cyclical loads.

If you wonder how does it generate energy it is with an alternator system with coils and magnets. The cool part is that, unlike wind turbines, you do not have gearboxes, shafts or any other rotating element. The benefit is not only less maintenance but also a noiseless operation.

An additional interesting characteristic of this technology is that many machines can be clustered together in a narrow space. Standard wind turbines have a distance of hundreds of meters from each other to avoid the wake effect (basically the turbulence in the wind caused by the turbine itself). The wake effect can have an impact not only in the energy production of the turbine but also on its lifespan, shortening it due to the demanding operational conditions.

On the other hand the bladeless solution thrive on turbulence so you can pack more Tacoma Vortex together in what would probably look like a forest of artificial trees.

Another very cool feature of this machine is its ability to change its rigidity to adapt it to the characteristics of the wind. Different environmental conditions will request a different setup from the vortex in terms of mass distribution and rigidity. According to the website of the developer the machine will be able to automatically “tune itself” in order to maximize the oscillations.

How many of us are there? Wind energy sector employees

Workers in Renewable Energy. Copyright Statista (one of my favorite website)

It is no secret that the wind business is going through a turbulent period, with several players in the sectors experiencing a tough time.

I was wondering how many people are currently employed in Wind and I have found this interesting report from IRENA (the International Renewable Energy Agency).

I have discovered several interesting things:

  • Only 11 million people are working in renewable energy job. Not that many, if you consider that we are 7.700.000.000.
  • Out of these 11 million, only 1.1 million people work in wind. The biggest share is Solar PV, with over 3.5 milions.
  • The majority of wind job are in China. With an incredible 44% of jobs in the People's Republic of China it looks like I will have to improve my Mandarin.
  • One out of three is a woman, above all (45%) in administrative jobs but also (around 30%) in technical function. This is more of what I thought.

 

Wind turbine tower as a water battery: the Gaildorf Wind-Water Project

Did you ever think at the amount of empty, unused space in the bottom of a wind turbine? Any idea how to use it?

Well, the folks at Max Bögl (a German conglomerate active in several sectors) have decided that it could be a good idea to fill it with water (about 40.000 m3 per turbine, up to a height of 40 meters) and use it as a temporary energy storage, in what they call a “water battery”.

Basically, the idea is to use a pumping system to fill the bottom of the tower when energy consumption is low and production is high (for instance, during a windy night).

When needed, the water can be released opening a valve and, thanks to a network of pipes with a diameter of over 1 meter, it can be used to produce energy through three Francis turbine, with a total nominal power of around 16 MW.

The hydro electrical plant is relatively near, at a distance of around 3 Km and with a height difference of 200 meters.

The turbines installed are 4× 3,4 MW GE 137 on an hybrid Max Bögl tower. What is remarkable is the hub height, varying from 155 to a record 178 m. They claim this to be the highest onshore turbine tower currently in operation, and as far as I know with a tip height of 246.5 metres, this could easily be true.

The switching time between energy storage and energy production is not exceptionally fast (30 seconds) but is not outrageously long either.

Partially founded by the German Environmental ministry with over 7 mln. € the pilot project is currently being built in Gaildorf (southern Germany).

Among the benefits of this solution is noteworthy the high efficiency of conversion of the potential energy of the water into electricity using well-known, proven technologies.

The main issue that I see is that this system, to be implemented, need a hydro electrical plant nearby with his own “long term water storage basin”. Essentially the wind turbines are providing only an additional (and somehow limited) storage capacity. However, in order to be cost effective, this technology will also need a “standard” basin.

Order out of chaos: Risk Breakdown Structure

There is a good number of techniques that can be used to identify risks.

Some are techniques focused looking at past (every Tender Manager should be able to create a list of issues he had experienced in past projects), other tools are focused on the present (spending a few hours reviewing your current assumptions should help you identify a good number of “what if the assumption is wrong” risks) and other help you to think forward (for instance, a good brainstorming session with stakeholders and experts from different departments).

The outcome of such techniques is a list of risk, usually very long and, above all, unstructured. A qualitative risk assessment can be done, attributing to each risk a “probability and impact score”. My impression is that such exercise is somehow arbitrary (although this is probably better than nothing). What is not provided by the qualitative risk assessment is some visibility on risk patterns, concentrations of risks and correlation between risk causes.

An interesting tool that can be used for such scope is the Risk Breakdown Structure (RBS). Inspired by its more famous counterpart, the Work Breakdown Structure (WBS), it is basically a hierarchical structure (a “taxonomy”) defining several categories and sub-categories for risks. For a wind farm, an example of RBS could for instance consider at the first level the project, the customer, the management (internal) risks and the environmental risk.

Here I’ve made a very rough, unfinished example of how a RBS for a wind farm could look like – as I think it is an interesting exercise I will try to expand it and complete it in the future:

Which are the benefits of such approach?

I believe that the most important one is the identification of high-risk areas: are the majority of your risks coming from the same area? This can help focus the efforts on the most critical aspects. "Majority of risks" should not be considered the absolute number of risks (you can have dozens of low severity risks in the same area). A better way to do it would be to assign a numerical value to each risk, the "Probability x Impact" score and sum the value of such risk scores in all the areas (level 1), subareas (level 2) or sub-subareas (level 3).

Once it has been properly developed the RBS itself can also be used as a checklist for risk identification in future tenders or projects (assuming that your organization is working at comparable projects, as it usually the case in wind farms).

Last but not least, the RBS can be used to compare the risk level and concentration of two or more different tenders or projects, possibly weighting the lowest level risks with their probability / impact score.