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.
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.
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.
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.
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.
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.
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.
One of the key deliverables in project risk management is the risk register.
The idea is that after risk identification, qualitative and quantitative analysis, and planning of risk response the tender manger (or project manager) should end having a list with all the risk identified at that point in time.
I assume that the content and format of the list will vary depending on the type of project and organization. However I believe that it should include at least:
Impact on objective
Risk response strategy
The Project Management Institute add to this list other concepts like category (the taxonomy of risks always looked somehow arbitrary to me), probability (even more difficult to define with accuracy in many situations) and cause.
If you are familiar with the topic you will remember that, if a risk materialize, it will be moved from the risk register to the issues (or problems) register.
And here the interesting parts – I have been reviewing some risk registers that I have done in the past noticing that the description of risk was mixing three different concepts – cause, risk and effect.
“Presence of strong Workers Unions in the area”, for instance, it is not a risk: it is a fact, a reality in several projects I have been involved.
The risk is to have many strikes in the construction site – the effect would be delays (impacting the “to be on time” objective) and payment of damages (impacting the “to be on budget” objective).
There is a proper way to fill the risk register: the use of risk metalanguage.
Risk should be expressed in sentences with this structure:
“Because of <cause>, <risk> might occur, which would lead to <effect>.”
This language construction help bringing clarity and logic to the risk register. The previous example would become for instance:
“Because of <the presence of strong Workers Unions in the area>, <many strikes> might occur, which would lead to <delays and payment of damages>.”
There are some interesting implications. For instance this structure should be used in different languages – I would be curious to see if it can be replicated easily in all of them.
Additionally, it force you to think at the logical correlation between the causes of risks.
For instance, you can think at different situations were the same risk can have 2 different, independent causes:
“Because of <cause #1 AND cause #2>, <risk> might occur, which would lead to <effect>.”
I understand that in this case it should be split in 2 different entries of the Risk Register.
However in some situations two or more different causes need to be there at the same time for the risk to materialize:
“Because of <cause #1 PLUS cause #2>, <risk> might occur, which would lead to <effect>.”
Obviously you can increase the complexity ad libitum, as the same risk can have more than one effect:
“Because of <cause>, <risk> might occur, which would lead to <effect #1 AND effect #2>.”
I guess that also in this case the good practice is to split the sentence in two different entries for the Risk Register.
Basically it is an Australian company using “rock slingers” (that is, conveyors belts connected to a dumper) to backfill trenches mounted on small vehicles (2.5 meters wide). The equipment is made by CAS, an American company specialized in this kind of equipment.
It is a remotely controlled machine that can create the sandbed inside the trench accurately and at a great speed. According to the figures provided in the website the slinger can create 16 Km of bedding in a day, using up to 1000 tonnes of material.
I guess that they call it "slinger" because it can throw material at a quite remarkable distance (over 40 meters). Used in combination with one or two trencher it looks like it can lead to relevant savings, less labor and a more homogeneous distribution of the material.
I have received an email from Penelope Smith from Rockslinger on the topic. As I beleive it can be interesting for several readers I'm including it in the post below.
Hi Francesco, We are involved in many civil projects involving backfilling trenches and 'Rockslinger' is our trademarked brand of high speed conveyor equipment in Australia. It's super to see the machinery becoming noticed in the renewable energy sector, such as the other operator you mentioned in your blog.
Our site is www.rockslinger.com.au and we are the largest slinger fleet operating in the country. This type of machine actually speeds up the process of installation at the trench and material spreading stage incredibly using this equipment.
It has a movable arm and is externally operated if needed with advanced drive ability. The application rate is a tonne a minute accurately laid at the contractor's required depth.
We have found that the renewable infrastructure sector in Australia, including wind farms and solar farms, are beginning to realise the saving in construction when using more efficient machinery. I've had a read through your blogs and really appreciate you sharing your experience.
Now I've found your site, I'll keep an eye out for the next blog. Thanks again.