A website about wind farm construction: not only turbine erection but also balance of plant – access roads, crane pads, turbine foundations, power collection network, substation, meteorological mast and the economics behind it.
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.
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.
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).
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.
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).
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.
I will try to answer this question: what is the better tool to manage the information obtained on site?
There are several very useful mobile apps that can help us finding the target locations and geolocate the position of all relevant elements of the project (wind turbines, substation, roads, crane pads, etc.).
They can also help us obtaining and storing information in an efficient and organized way.
Although none of these software has been specifically created for the wind business´s needs, they offer very useful features that could make our lives easier during a site visit.
As they are mobile apps, we should make sure we have enough battery and that is why I always recommend bringing a portable charger with you.
Google Earth / Google maps
These two apps are by far the most popular. Anybody who is familiar with the desktop software will rapidly recognize their strengths integrated in a very powerful GUI.
They allow the user to load kml files with very valuable information such WTG positions or road alignments or even connect to maps edited and stored in our personal Google account
I see three main drawbacks here:
The basemap loaded in the background is limited to the basic formats: Street, Terrain, Traffic, Satellite, etc. Unfortunately they do not offer the chance to insert our customized maps as a background.
The geolocation is based on the device´s built-in GPS, but the background map data is loaded only if network is available – and this could be a big risk in remote areas.
They are not really prepared to create and store points of interests with comments and link personal photos taken in the area of study – or at least, not as I would like.
This app uses the device´s built-in GPS so that the correct positioning does not depend on the availability of the network.
One of the main advantages compared to the traditional GPS mapping apps like “Gaia gps”, “Google Maps” or “Google Earth” is that Avenza maps allows the user to import our own customized maps in different file formats such as geopdf, geotiffs.
These maps can be any kind of project drawings created with GIS tools such as QGIS or ArcMap.
This app can be used for free. With the free version we can download up to a certain number of maps at a time (usually 3). There is also is also Pro version which includes more features and increases the possibilities.
It also includes the option to create a store account. It is not required but is recommended though.
For more information about this tool, I recommend you go directly to the official web.
This is a tracking map app used mainly by hiking lovers.
Initially, it looks like a very simple app without any special charm. However, it offers similar functionalities to “Avenza maps” and I personally consider it gives a good service to the actual needs in a site visit.
The main advantages are:
We track our routes and the elevation information (longitudinal profiles) is registered as well.
The photos taken along the routes are georeferenced and can be visualized over the route.
There is the option to add “Places of interest” with comments.
We can create our customized maps either by using the app or from the desktop tool called “Maprika map designer”. See below a link with a tutorial explaining how to do it.
As a drawback, we can considerate the lack of confidentiality: any map uploaded containing relevant wind farm information would be available to any user from the server.
Furthermore, it is quite easy to upload a map to the server but deleting is not as straightforward.
I leave to the end which, from my point of view, is the most promising from all the apps listed here and, surprisingly, maybe the less popular: Road AI
The first time I heard about this tool was in a Finish project I was involved in.
One of the contractors used to work with it and it ended up being a really nice discover.
Although addressed to cover infrastructure management, it can be “recycled” to work as an information management tool for site visiting. The mobile application provides a dynamic and flexible way to collect, manage and deploy data in a user friendly environment.
The main strengths are:
The user can record videos and make photos of the construction site which will directly be stored and available in a cloud service. E.g. We can make videos using a phone holder on the windscreen to record routes and the time and the GPS location will also be saved.
Make annotations associated to the audio-visual material recorded on site.
View all of the recorded routes and sites together with the annotations and metadata using the map interface available through a normal browser application.
We can share this information with anybody inside your organization or with a client.
It also allows to use filters and requests to visualize data following a certain criteria with a similar philosophy than in a GIS environment.
Surprisingly, it is difficult to find any reference to this application out from the local Finnish market. Only a few references are found in works at UK.
This is a link to the first of a series of video tutorials explaining the way to use and take most of the system (sorry it is in Finnish):
All in all, the proposals presented here are only a sample among a big offer presented in the market. Any tool with similar properties would work well enough used in a proper way. It is just a matter of personal preference as long as an ad hoc and convincing system is deployed and released into the market. Maybe one day…
Behind every wind farm project there is a technical feasibility study, made to assess the potential for electricity generation of the selected site.
At the beginning of the wind farms era wind speed and wind direction was estimated using data from existing weather stations.
Due to large differences between predicted energy production and actual generated energy (which was usually overestimated) meteorological met mast are now designed and installed to have better estimates.
Any estimate of the Annual Energy Production (AEP) contains several uncertainties and paramethers that can vary such as:
Duration, tower setup, anemometer quality.
Long term adjustments
Selection of a long term wind data source, correlation and long term prediction methodology.
Linear model, computational fluid dynamics models, mesoscale for estimation from met mast into none measured positions.
Horizontal and vertical extrapolation
Horizontal and vertical distance from the meteorological mast(s) to each Wind Turbine Generator (WTG) position and hub height.
Wind speed to energy
Use of a wind turbine calculated/measured power curve together with the site conditions wind speed to estimate energy (if within constrain inflow angle, wind shear, etc).
Calculated losses i.e. electrical, environmental, curtailment, wake model selection.
Uncertainties and paramethers affecting wind farm energy production estimates
Giving all these project uncertainties, an AEP can be calculated with different levels of confidence in the results.
For instance, what is called a "P50" is a production expected to materialize in 50% of the cases.
It is possible to estimate more conservative energy productions, such as for example P99 (a lower production value, that should materialize in the 99% of the situations).
The wind site resource assessment is a careful identification and evaluation of different risks and uncertainties sources that are unique for each site.
In this article we will focus on two uncertanties, arising from the horizontal and vertical extrapolation of data.
For the vertical extrapolation we can identify two sources of uncertanties:
The difference between measurement height and hub height.
When using a lower met mast compared to the selected WTG hub height different methods can be used to estimate the wind speed either by extrapolating for example with a power law/log law method.
The altitude difference (flow model)
It is possible to reduce the first vertical uncertainty by installing a met mast with a top anemometer at the same hub height.
Alternatively remote sensing devices such as a Sodar/Lidar can be used on site.
It is recommended to have a wind speed measurement of at least 2/3 of hub height to keep uncertainties at an acceptable value, as any methods for hub height wind speed estimation (i.e. power law or flow model) will add uncertanty to the calculation.
A typical range for this uncertainty is in the 1 to 4% range, varying depending on the type of terrain and the total vertical distance (for example, 0.5% per every 10 meters vertical difference).
The Horizontal Extrapolation is heavily influenced by the terrain and surrounding vegetation.
One of the reasons is that certain orographic traits (plain, rolling hills, mesas, mountain ridges) and roughness (native vegetation, agricultural, forest, lakes) at the measurement position should be “similar” to the WTGs position for the flow to behave in the same manner.
A typical range for this uncertainty is from 1 to 4%.
According to Measnet the data from a met mast are representative only for few km - up to 10km for a simple terrain and around 2km for a much more complex terrain.
After the assessment of 200 projects DNV-GL identifies the horizontal and vertical extrapolation to be responsible for approximately 35% of the total energy uncertainty.
For projects with a high spatial variation (i.e. with turbines very far away from each other) the value can be as high as 51%.
Depending on the wind farm total size, terrain characteristics and mesoscales effects this values can be even higher.
It interesting to note that even if two projects have the same P50 AEP, the one with lower uncertainties and therefore a higher P99 AEP will have better chances to be built being more "bankable".
Conclusion: very early in the project, after just a few months of measurements, the Horizontal and Vertical uncertainty should be calculated and simulated in cost to benefit financial model to find out the best quantity of measurement locations to have.
A factor to consider this important topic in the initial period is to be able to carry out correlation between measurement locations and assess flow model cross-prediction errors that will further reduce project uncertainties.
Today many resources can make the engineer life´s easier helping create a renewable energy project in any spot of the world.
Powerful GIS and CAD software and an incredible amount of data available from either public or private entities make possible designs with a sufficient level of accuracy to have good cost estimations, even at early stages of the project.
However no tool is good enough to give you the amount of information a site visit can provide. This is a step that can give a boost of extra quality to the design process.
Whenever possible, doing a visit to the project area is highly recommendable.
There are many circumstances which could make it impossible, such as aggressive delivery dates, excessive travel distances or lately pandemics.
Also priorities matters: we cannot compare the preliminary work needed for a tender phase in a very early stage with the final detailed execution design of a constructive wind farm project.
In this article I collected some tips to successfully plan a Site Visit:
Hiring a 4x4 car (4 Wheel Drive or similar) is a must. Take into account that we will usually find unpaved roads in uncertain conditions or even no roads at all.
Depending on the actual state, it would be wise sometimes pulling over, park the car and go to the targeted place walking.
Furthermore, companies are already offering already internally a 4x4 off road driver training. We can find a lot of difficulties and a skilled drive behind the wheel is a blessing. See below the state of a track in a recent site visit… Yes, we were able to arrive home safe.
Food and breaks
It could be the case that the site is in the middle of nowhere without direct access to any populated village. Even if that is not the case, we will have to assess the convenience of having lunch in a restaurant or canteen with the risk of losing valuable time in the travel. Anyway, we must prepare and take with us some food (e.g. sandwich and fruit would be a good combination) and enough bottled water for the whole journey. Short breaks every 3-4 hours to have some rest and eat some snacks is also highly recommendable. A well planned visit should have account for this moments and there should not be excuses for skipping them.
Clothing and HSE
For a good feet protection, construction security boots with reinforced toe will serve well enough. If construction has not started yet, hiking boots could be another option. Waterproof resistant trousers or, alternatively, with resistant fabric are also recommended. On the other hand, we should follow some common sense rules such as taking a hiking cagoule (raincoat) if we are expecting rain or a cap, sun glasses and sun protection for hot and sunny days.
A careful study of particular conditions at the project site shall be done to avoid any surprise.
Reflective vests were needed in a visit I made to Sweden because the wind farm was in an hunting ground. Anybody without proper clothes hiking in the mountains was in danger of being shot.
Another example was a visit I recently made to Australia. It was in December and the wave of forest fires was at its peak. Of course, temperatures raised easily to 35-40ºC and the initial temptation was to use short sleeved T-shirts. The fact is that the project area was full of ticks and a complete protection of the body was required to avoid any undesired surprise. I found myself shaking some of them out of my shoulders.
To make the most of our trip, we need to carefully plan our journeys beforehand.
Here goes a proposal with some key aspects. How to organize them will depend on the particular circumstances of the project:
If a route survey has already been done, follow the route sketched from the point of discharge (usually a maritime port) of the WTG components to the wind farm site and make sure that the report matches the reality. If there is not a route survey in place, try to find alternatives on site. If there is more than one option, we can use one route to go and other route to return.
Visit to the nearest towns or villages to assess the best place to stablish central headquarters and/or employee’s accommodations. A project execution phase will normally take, in the best scenario, several months. Finding a place within a one-hour radius to the construction site with leisure offer and good services will contribute to a keep the teams spirit up. As a rule of good practice, it is recommendable talking with the locals, as they will always be able to provide valuable information.
Go to commercial quarries close to the site. It is always good to know quality and properties of the available material, unit costs and availability. In general, no appointment is required but it would be a rule of good practice calling before to know whether anybody can receive us.
If not already defined, search for possible places to stablish the site compounds.
Inspection of suitable areas that may serve as storage points for the WTG components.
Check all the WTG positions one by one. As a rule of thumb, experience says that a realistic planning should contemplate a properly assessment of a range between 10 to 15 WTG locations. Of course, it will always depend on the site conditions, the state of the existing roads and how far the positions are from the nearest driveable path.
Visit to the substation area and the point of connection to the existing electrical network.
Of course, there will be always unexpected events that we will have to handle once on site. However, taking the good habit of following these rules before travelling reduces the odds of facing undesired surprises as well as gives the engineer the chance to work in a more efficient way and even enjoy the journey.
As wind turbine loads and foundations size keep increasing year after year sharpening the geotechnical calculations and modelling correctly the interaction between soil and foundation is becoming a priority.
The cost of foundations can represent a significant percentage of the investment in a new wind farm - even more in 2021, when steel and concrete are becoming every day more expensive.
An important topic that is becoming the focus of detailed studies is the soil bearing capacity degradation under cyclic loads.
This subject has been incorporated in the new version of the standard IEC61400-6 on Wind energy generation systems in Part 6: Tower and foundation design requirements.
Now, under certain conditions, a certain amount of "gap" below the foundation may be allowed.
“Gap” means that under certain situations the ground below part of the foundation might become uncompressed – as if the foundation was partially lifted, creating a "gap" (i.e., a separation between the structure and the soil).
This is something that previously was not allowed (unless the foundation was on rock).
The reason is that if the soil goes through several cycles of compression and decompression its bearing capacity might deteriorate. Basically the bearing capacity becomes lower and lower, putting at risk the stability of the structure.
This is a relevant change, as the IEC standard is one of the most important document (if not the most important) used in wind turbines foundation design.
The key idea behind the change is that if the soil below the turbine is not susceptible to the phenomenon of degradation under cyclic loads a certain amount of gap can be allowed.
Removing this “no gap” requirement means that a significant reduction in the diameter of the foundation can be achieved.
This happens because otherwise the foundation would have been bigger only to keep the soil below it always compressed.
The “no gap” requirement used to be one of the dimensioning constraints in wind turbines foundation design when the soil was good.
The key to allow some gap in the foundation design (and as a result, a smaller foundation and savings in concrete and steel) is to be able to justify that the soil characteristics will not will not degrade under cyclic loads.
This involves dynamic tests, which are time consuming, expensive, difficult to implement on site, unusual for most geotechnical companies and difficult to post process and interpret.
In some cases, even with a robust testing campaign, additional finite elements models have to be created to validate the design.
Will we see smaller foundations after this change in the IEC? We will need to wait several months to answer this question.