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

Concrete laminar wind turbine foundations: doing more with less

Concrete laminar foundation (or CLF) is a new type of wind turbine foundation developed by my friend José Carril and the team of MS-RDITECH.

The CLF foundation is a new wind turbine foundation concept based on laminar elements.

It is composed by 3 main elements: a lower slab, a central cylinder and a top shell.

The anchor cage is used to hold the 3 elements together with the prestressing required to attach the tower to the foundation.

The voids between the different laminar elements are filled with lightly compacted backfill.

Developed and patented by MS-RDITECH (a Spanish engineering firm, subsidiary of MS-ENERTECH) this solution face the current challenges in the on-shore wind turbine foundations industry.

Turbines in the 7 to 8MW are consuming over 1000m3 of concrete for each foundation.

That creates different issues: economical (costs are huge), logistical (not easy to produce and transport such quantities) and technical (it is very challenging to pour that amount of concrete without creating execution joints).

This foundation creates an effective alternative that reduce costs rationalizing the concrete volumes while trying not to increase the execution complexity.

The construction process is in-situ, with 3 different concreting phases:

1. Reinforcement and casting of lower slab

2. Reinforcement and casting of central cylinder

3. Reinforcement and casting of top shell

To avoid using internal formwork voids are backfilled. This backfill act as internal formwork and as a working platform for the subsequent reinforcement works.

This technical solution uses less material due to its geometry, reducing the concrete and steel amounts.

Other advantages of this solution it is the versatility. If needed, precast elements can be used. In some situation this could lead to savings or a quicker installation.

MS-RDITECH is currently working at a prototype of this foundation.

It is worth noticing that the concept of laminar foundation is not new in civil engineering and in the building industry. For instance, it has been used in the Stuttgart TV tower and in similar industrial structures.

How relevant are the savings?

A 7MW wind turbine can easily use more than 1000 m3 of concrete and  120 to 150 Tn of steel reinforcement. This solution use approximately 40% less concrete and 10% less steel, so the savings could be in the 50.000€ range for each foundation (the actual number will depend obviously on the specific with turbine model, the geotechnical situation and the cost of materials and manpower.

Road Design & Earthwork Optimization Software for Wind Farm Networks

I have been contacted by Erin Wasney, Business Development Manager at Softree Technical Systems.

She proposed to write a guest post on RoadEng, a software developed to design long roads and large networks of low volume roads faster and easier than other civil design software.

I am more than happy to share his post with you.

(Beginning of guest post)

Onshore wind farms often require a large network of roads to install and access turbines, and as previously shared by the team at www.windfarmbop.com there is often a need for quick planning and analysis. As followers of the blog, we were inspired to share some information on our software, RoadEng.

The video below shows an example of a wind farm project created in RoadEng Civil Engineer. As a software tool, RoadEng is a detailed geometric design software, but its focused functionality allows for it to be used for quick planning, analysis and visualization.

Created more than 30 years ago to support the design of forest road networks in complex terrain, RoadEng is now being widely used in renewable energy projects. There are many similarities between the requirements of forest road networks and those required to develop and maintain windfarm projects, mainly:

  • Projects are often time and cost sensitive, both from a planning and implementation standpoint,
  • Road networks are usually low volume resource roads that may include greenfield construction or upgrades to existing access infrastructure,
  • Pads and/or landings are usually required and built as part of the road portion of the project,
  • Location of the road is often influenced by other project factors and being able to quickly update a road design to account for other project parameters is important to help facilitate timely decisions and avoid expensive redesigns often encountered when using slower, less dynamic/interactive software, and
  • Often the personnel planning the access infrastructure have additional roles in the project.  Having a fast, easy-to-learn software that doesn’t require a drafting background to quickly become proficient makes adopting RoadEng as a design platform easy but more importantly reduces the need for more project personnel.  This often allows decision makers to have a more wholistic understanding of the project, do more design themselves, increasing productivity, and avoid some of the challenges associated with design review and communication.

In RoadEng, the horizontal and vertical alignments are connected, and a cross section geometry is attached to the 3D centerline automatically.  Pre-built customizable components make building smart cross section geometries easy, and in situations where more complicated cross sections are required (as in the video below), components can be combined and/or linked together:

As the user creates or adjusts their alignment, all aspects of the design update in real time; no need to manually prompt the software to recalculate and since the software is light, users can avoid having to deal with the frustration of click-wait, click-wait, click-wait as their computer struggles to keep up with the computation requirements. In other software, it is common for users to truncate their projects into short, workable segments to reduce computing requirements, in RoadEng it is not uncommon for users to do detailed designs for multiple alignments in a single file for roads over 50km long and based on large LiDAR data sets.

Aside from just considering site geometry, road costs are often significant and are worthy of careful consideration during the design process. RoadEng offers several tools that help designers quickly evaluate how much effort is required to build a project.  These tools include:

  • Traditional mass haul diagram, with cut and fill quantities
  • Opti Haul diagram, tracking excavation and fill volumes by material type; solving for optimal material movement by individual material types, definable quality requirements and movement direction constraints
  • Alignment Costing, including an ability to easily compare alignment options and get the associated sub-grade construction costs for each option (we call this “design time costing”).

Finally, construction costs and time spent designing can be further reduced by using Softree Optimal. It is a patented earthwork optimization add-on tool for RoadEng that can help reduce costs by generating a vertical alignment that minimizes earthwork costs (embankment, excavation, and movement costs for sub-grade materials).  According to a study completed by FP Innovations (2017) on low volume resource roads, vertical optimization reduced the estimated construction cost by 13% to 22%, on average, depending on road design standard.

Other notable functions included in RoadEng for wind farm design:

  • 3D symbols for turbines – allows for visualization of the turbines in the context of the roads and pads
  • Drainage tools – hydrology tools and watershed calculations, as well as a culvert editor tool for quick additions of culverts and cross-drains to projects
  • Graded pad object optimization – balances cut & fill for graded pad objects
  • Multi-Plot report builder – semi-automated creation of construction documentation
  • Field-focused tools – creation of Avenza georeferenced maps, GPS integration during design

Although not ideal for every civil engineering project, RoadEng performs well in rural infrastructure applications, particularly for quick planning and analysis, as is often the case for wind farm road networks.

From blades to cement - the experience of Veolia

A few days ago YouTube’s algorithm correctly has correctly suggested to me to have a link at this video.

Made by Business Insiders is an interesting addition to the theme of wind blade disposal – have a look at my previous post on the topic on how to use blades to make cement.

You will see that first GE has to pay Veolia to get the blades and that subsequently Veolia pays to send the final product to cement factories. This suggest that the technology is not cost effective yet.

I also notice that the video mention that the blades are between 8 and 12 years old. That’s very unusual – the typical life of a wind turbine is 20+ years (some are reaching 30 or even 35 years).

Self-erecting turbines: the Elisa / Elican project

Elisa floating offshore wind turbine

The Elisa / Elican Project is a multimillion, full-scale prototype of a self-erecting offshore concrete tower.

The tower is coupled with a buoyant foundation – it floats and can be transported to the installation site where it is ballasted and sunken to the final position.

Once in place the tower self-erection can start, saving money on one of the most expensive items in offshore installation: the specialized vessels with cranes usually used.

The wind turbine is installed in the harbour, and as the tower is still “folded” a smaller crane can be used.

After the installation of the WTG an auxiliary floating system is used to stabilize the structure and the foundation is towed with tugboats. The auxiliary element is the yellow structure that can be seen in the picture below.

Elisa floating offshore wind turbine towed in place

This solution is applicable for a water depth in the 20 to 50 meters range.
The prototype has been founded with 3.5 ML€ by the EU and it is developed by a consortium led by Esteyco, a Spanish engineering company from Spain that developed several others very interesting projects such as the braced foundation.

The development of the solution started in 2015 and went through several stages (numerical modelling, tank tests campaigns, working prototype).

The prototype is equipped with a 5MW WTG (from the pictures I would say a Siemens-Gamesa) and it is obviously equipped with numerous sensors (inclinometers, accelerometers, etc.).

According to Esteyco, he two main distinctive features of the project are:

A self-erecting telescopic tower, which brings down the center of gravity during the temporary installation stages, enabling ground breaking possibilities in the installation process and providing full independence of costly and scarce offshore heavy-lift vessels which have become a bottleneck for the sector both in terms of capacity and availability.

An economic foundation base which (…) can temporarily act as a self-stable floating barge over which the complete system can be pre-assembled in-shore at low drafts and low heights and effectively towed to the site, where it is ballasted to rest on the seabed.

As you can see in the following picture, the tower is a hybrid solution (concrete & steel).

Hybrid offshore tower

While this is the first time that I see a full scale buoyant foundation that is subsequently sunken there are other self-erecting concepts being developed in the market – see for instance the Nabrawind idea.

Do we really need towers and foundations? Airborne wind farms

Airborne wind power with air generated energy. Image copyright Philip Bechtle et al. - "Airborne wind energy resource analysis". Article on "Renewable Energy" 141 (2019)

Airborne wind energy is a generic name that describe various technologies that have different levels of development.

They have in common the idea of using unmanned vehicles such as planes, kites, balloons or similar solutions to produce energy from the wind. These vehicles are generally “tethered” (that is, connected to the ground).

Their main promise is to give you “more energy with less material” – because they have a lower initial cost and they consume less material. They also have several other potential advantages. For instance, they could be deployed relatively quickly in areas where there is urgent need for electricity (for instance after a disaster).

Researches on this technology started in the seventies but accelerated greatly in the last 10 to 20 years, with dozen of company developing different ideas and registering hundreds of patents.

There is still no consensus on which is the best technical solution. Therefore there are significant differences between the technologies currently being developed.

A first distinction can be made between systems that produce energy in air inside the flying unit (“on-board generation”) and those that have a generator inside a ground station.

This ground station can be fixed or move (for instance on a loop track or an horizontal track). There are different possibility to produce energy in the ground station: for instance, the tether can unroll a cable around a drum, and the rotation of the drum can be used to produce electric energy.

This mechanism remember somehow a yo-yo – you can see how it looks like in the following picture.

The system work with a two-phase cycle: a "generation phase" where energy is produced and a "recovery phase" where the rope is rolled up again changing the flight configuration (and possibly, consuming some energy using an electrical motor to rewind the rope).

Airborne wind power with ground generated energy. Image copyright Philip Bechtle et al. - "Airborne wind energy resource analysis". Article on "Renewable Energy" 141 (2019)

Several others possible categorizations are possible, for instance depending on the wing type used by the system (rigid wings vs. flexible wings), their weight (lighter vs. heavier than air) or considering the take-off mechanism used (vertical vs. horizontal).

Rigid wings have a better aerodynamic efficiency. Additionally, they usually also have a longer durability. Soft wings, on the other hand, are lighter and more effective with ground generating systems (decreasing the flying mass increase the tension on the cable).

How high will they fly?

The objective is to fly higher that the current wind turbines, to find stronger and more consistent winds (as a general rule the turbulence of the wind decrease with height).

Although it would be nice to extract energy from jet streams at 8000 meters (the strong winds blowing in the upper atmosphere that can make your airplane fly faster) there is evidence that at such altitute the cable that connect the vehicle with the ground would dissipate a significant amount of energy due to aerodynamic drag.

This could imply operating the system at a much lower altitude – probably in the 200m to 2000m range, with an optimum that will be location specific.

Investigations are also focusing on how to solve the take-off problem: as the vehicles are not propelled they will have a very low speed during take-off, and this imply less controllability of the vehicle.

The inverse problem (landing) is equally relevant: it should be possible to stop the system quickly in case of an emergency, as it is possible with a wind turbine.

To solve these problems and to maximize energy production the companies working in this niche are using algorithms to control the flight.

Another problem that the engineers are trying to solve is how to find a balance between low cost and reliability: these machines have moving parts and are supposed to have a long useful life (at least compared to the current lifespan of a wind turbine, which range from 20 to 30 years). The cost of maintenance should not offset the low initial investment cost.

Making a prediction on “social acceptancy” is much more complex (and not only because I am biased and I believe that wind turbines are beautiful).

There is some possibility that people will think that kites and balloons are more attractive than standard wind turbine. Can you imagine a wind farm made from giant helium-filled balloons? I'm sure my children would love it.

A floating wind turbine. Image copyright Altaeros Energies

However, the path towards the implementation of these solutions still seems long and complex.

A few months ago (February 2020) Google closed Makani, one of the companies more advanced in the research for airborne turbines.

Makani was a start-up founded in 2006 and acquired by Google X in 2013.

Makani made several working prototypes and was considered in pole position to find a working solution, also because their parent company has very deep pocket. Therefore their closure was a shock for the industry.

We will probably still need towers and foundations - at least for a while.

Modifications to wind farm access roads: a step-by-step guide

One of the problems that occurs frequently to engineers working on wind farms is how to modify existing access roads to allow the transit of special vehicles.

I was contacted by several readers of the blog who had this issue - the last one was Egil from Norway who led me to write this article.

In general, the problem is usually a curve that is too tight, a change of slope that is too fast (i.e., a road crest in the vertical alignment where the change of slope is too sudden and the truck “hits” underneath) or a combination of the two.

I am describing in this post the procedure I have followed in the past. If you have followed different steps please drop me a line.

The example is taken from a project where the blade truck was hitting below (there is usually very little space under the trailer – as little as 20 centimeters).

The first step is to send a topographer to create a cartography as detailed as possible of the area.

Both GPS and “traditional” topography will be fine while I would avoid LIDAR because you would have too many points to work with. It is sufficient to work with a simplified model.

You will usually receive the results in AutoCAD DXF or a similar format, ready to use.

The next step is to create a tridimensional model of the existing road. I usually work with AutoCAD Civil 3D – however there are several similar software in the market.

Then I use AutoTurn to calculate the path of the truck. I really like this software as it gives me a very reliable simulation of the wheel path and the swept path area.

AutoTurn simulation of the the path followed by the truck. The problem area is on the bottom.

The following step is to use Civil 3D (or your favourite software) to calculate longitudinal & cross sections (representing the ground "below the truck" and "as seen from the wheels")

This help me deciding if and were changes to the existing roads are needed. You can see in the image below where the trailer is "touching" the road. In this example I was already aware of the problem as I was contacted by the colleagues on site.

A section showing the blade trailer (hatched rectangle) and the elevation of the existing road below. As you can see the truck is hitting the ground below.

The next step is to modify the geometry of the road "manually".

This is done changing the elevation of the points in the topography one by one in the area of the problem recalculating the longitudinal profile and the transversal sections until I reached a shape that looked OK in terms of torsion, slope and free space below the truck.

The elevation of the problem area before and after (points marked in red)

You can see in the image above marked in red the points that I have changed. At two points the ground has been lowered, at one point it has been raised.

When you are satisfied with the solution you can export all relevant information (digital elevation model, cross section, longitudinal profiles, etc.) and send it to the topographer on site so that the changes can be implemented.

In the case of bends, if only minor modifications are needed, the same procedure can be followed changing points as needed.

Blade mover – a flexible dual transport system

The two elements of the blade mover

One of the many problems posed by the huge wind turbine blades currently in the market is how to move them quickly and safely.

In some situations (like in the factories, or when blades are temporarily stored before installation) space can be extremely limited and there is the risk of damages. Additionally manipulating and moving the blades can be a time consuming activity.

To solve this problem a Danish company (SH Group) has developed an interesting solution, currently used by a blades manufacturer.

The “Blade Mover” uses two elements, one at the root of the blade (a trailer pulled by a vehicle) and the other at the tip, where a self-propelled vehicle with a diesel engine is driven by a technician using a remote control.

The vehicle at the tip is extremely manoeuvrable, allowing full control on the steering wheels – you can basically orientate the wheels in every direction you may need.

The tip element - an independent vehicle

The system has been develop to carry blades with a weight up to 80 Ton.

I also see from the pictures and the YouTube videos that it use custom frames. The frames are connected to the blade mover using a flexible sliding mechanism with safety pins.

The tip frame. All components can be modified to fit a specific blade

One additional benefit of this system is that it can work on uneven terrains absorbing height differences with a hydraulic mechanism.

The blade mover in action. The technician is using a remote control system.

 

BoP vs. BoS - similarities and differences

Lately I have had the pleasure to spend a lot of time with my friend Alessandro.

Alessandro is an engineer specialized in the design and construction of photovoltaic plants – basically, a "solar energy" version of mine.

We spent some time discussing similarities and differences in the BoP (“Balance of Plant”) of wind farms and the BoS (“Balance of System”) of photovoltaic plants.

As you are reading this blog you will probably know that BoP and BoS basically mean “everything but the wind turbines (or the panels, in the case of BoS)”

Both can have quite an impact on the economics of the project. For wind farm is usually in the 20% to 30% range of the CAPEX while for solar plants it is typically much more – even above 50% of the investment total.

I have made a quick number with some projects currently under development in Southern Italy and I see that for medium size projects (10 to 20 MW) the cost of the modules is only 40%.

This could sound counterintuitive but is a consequence of the unstoppable reduction of the price of the solar modules. At the current rate the price is decreasing 75% every 10 years and this trend does not seem to change.

As a consequence, the BoS becomes every year more relevant (because it is not decreasing at the same rate, so its relative weight keep increasing).

Let's take a look at similarities and differences between BoP and BoS.

In both cases you will need internal roads and probably a substation to connect to the grid (unless the project is very small – for projects of few MW sometimes it is possible to connect directly to the grid in medium voltage).

Additionally, sometime the panels have a shallow foundation (“ballast”) that reminds somehow the shallow foundation of wind turbines on a much smaller scale.

Furthermore the engineering works to be done (geotechnical survey, topography, electrical and civil design, etc.) are very similar.

And this is more or less where the similarities end.

The differences are much more remarkable. For instance, a substantial amount of the BoS budget comes from the support structure of the panels, inverters and trackers.

Inverters are the elements that convert the electricity produced by the solar modules for DC to AC

Trackers are used to rotate the panels in order to have them always in the best position to maximize energy production. They are optional, but they are used frequently because they are generally a cost effective technology.

It is also very unlikely that you will see a solar plant on a steep terrain (with a strong inclination), while this situation is frequent in wind farms (many of them are placed on mountain ridges).

This happen because there is a limit to the height difference that can be absorbed changing the length of the elements that sustain the panels. Additionally, excessive height differences can make the work of the trackers more burdensome with an increased risk of failures.

For these reasons the usual maximum slope in a solar plant is usually around 5% or 6% - and therefore earthworks are limited and less expensive (at least compared to some projects that I have seen on top of mountains where a lot of blasting was needed).

For the foundations I mentioned before the shallow “ballasted” solution. This is basically a block of concrete holding the modules in place.

However the use of piles is usually more cost effective. Several alternatives are available depending on the geotechnical characteristics of the soil (helical piles where cohesion is low, driven piles when the soil is more dense, etc.) and in addition to the monetary advantage they are also usually faster to install and easier to decommission at the end of the life of the project.

Nabrawind Transition Foundation

Some days ago I have been contacted by Miguel, Sales And Marketing Manager at Nabrawind.

Nabrawind is a Spanish company working at several interesting breakthrough concepts – including a modular blade that I will try to describe in another article in the future, a self erecting tower and the innovative “Transition Foundation”.

Miguel asked me if I was interested in receiving material about the Transition Foundation solution they have developed.
I was obviously very happy to accept his offer and share with you what I have learned.

This alternative foundation use a 20 meters tall transition element in steel and cast iron in the lower section, at the bottom of the tower.

A detail of the transition element

The transition element is connected to the ground through three “feet” that allow different technical alternatives for the foundation: the standard solution (“shallow” or “gravitational”) plus two cheaper options – piled foundations (for standard soils) and rock anchors (when bedrock is very near to the surface).

The three alternatives solutions for the Nabrawind foundation - shallow, piled and with rock anchors

For a 4MW wind turbine the piles are expected to have a diameter of 1.5 meters with a depth in the 15 to 20 meters range.

A 15 meters pile would need approximately 80 m3 of concrete and 21 Ton of steel in total (that is, for the three piles).

This figure indicate very substantial potential savings in the amount of concrete and important reductions in the quantity of steel as well.

The piles are connected to the transition element via anchor cages (obviously smaller than the normal anchor cage used with standard solution).

In addition to the savings in the quantities the other main benefit of the solution is the speed. You will need only one or two days to drill the hole for the pile, and the installation of the reinforcement bars and concrete pouring is very quick as well (both operation should last between 2 and 4 hours in total).

The anchor cage variant promise to be even faster, needing only three concrete blocks (one for each “foot”) to level the surface and distribute the loads and 6 post-tensioned rock anchors with a length in the 15 meters range.

The Transition Foundation is more than a concept – the first foundations using this solution have been built in a wind farm in Morocco for a 3.6MW wind turbine on a 144m tower.

The have 24 meters long piles with a 1.2 meters diameter, for a total of only 81 m3 of concrete and 25 Ton of steel – a remarkable result.

How the foundation looks like (notice the 3 elements)

In the last picture you can see a detail of the completed works for the foundation.

How the completed foundation look like