Wood is Good for Wind

louis · 2021-09-26 09:19:03

I am sure this will be good news for those here who are concerned about materials usage in wind turbines...

https://www.youtube.com/watch?v=lJsznA1ug1w

Looks like wood might be the way forward for towers.

tahanson43206 · 2021-09-26 10:38:59

For Louis re #1 and new topic

Best wishes for success with this new topic!

I am NOT surprised that such a break from traditional hidebound thinking would occur in NewMars forum. I AM surprised that such an interesting idea should take this long to appear.

Since I know you like to create orphan topics, I understand you will not nurture it's development, but perhaps someone else will decide to adopt it.

If there ** is ** such a person in the existing membership, I would like to see occasional posts about the progress of this idea in the real world.

If (by chance) there is someone not already a member who would like to follow progress of this specific idea, please read Post #2 of Recruiting.

(th)

SpaceNut · 2021-09-26 14:42:58

Windmill of the past were made of wood from centuries long past. Many of these are still working to this day.

GW Johnson · 2021-09-26 15:04:14

I rather doubt the same wood lasts all those centuries, certainly not in the blade hardware exposed to the weather. Maybe some of the wheel-and-gear machinery that is kept inside.

I also rather doubt that wood-and-fabric structures can produce the high lift/drag ratio you can get with a more controlled shape-and-finish with plastics and metals. I also doubt the strength/weight is there to make 150-200 ft long blades. Very few spruce trees are that tall, anyway. Joints are heavy.

Now, the tower might be another matter. Although current practice for tall buildings is concrete and steel, with some aluminum sheathing, there is a movement advocating wood frame tall structures. It's small movement, but vocal. For all I know, it might actually work. But that use of wood does make the fire hazard much worse!

Just food for thought.

GW

Last edited by GW Johnson (2021-09-26 15:05:18)

tahanson43206 · 2021-09-26 15:17:13

For all who've posted so far .... has anyone actually watched the video Louis showed?

I haven't yet, but definitely plan to do so.

My hope was that the towers were to be built of wood, rather than the blades.

A tower made of wood can be enclosed in fire resistant material.

However, a fire in the gear box could be a risk for any tower. Iron burns after all, but I admit ignition point is quite a bit higher than wood.

It seems to me an obvious solution is to design the gear boxes so that they stop automatically when temperature exceeds some reasonable limit.

I've never understood why the fires that occur occasionally in wind generators are allowed to happen.

Is someone trying to save a couple bucks? (or Euros?)....

Or is this just another example of sloppy engineering, to which every organization is prey?

(th)

GW Johnson · 2021-09-26 15:42:30

I looked at it. That guy is quite interesting. Not far off the mark, actually. But, I stand by what I posted.

The fire risk has to do with the electrical hardware and the actual generating machinery. That stuff, if not detected in time, can blaze up. There is also the issue of lightning strikes (which ignite fires in combustible materials). If you build a wooden tower, you still must add something to ground it like a lightning rod. Otherwise, you increase the lightning strikes and the fires they cause.

Once you light off the wooden tower, you need a sprinkler system to put it out. Not just hold the line till the fire department can get there, literally put it out. Most fire departments would have no way to put out a fire in a combustible tower that tall. Same would be true of high-rise wooden buildings. (How inconvenient that I once worked in fire protection engineering, among so many other things.)

GW

Last edited by GW Johnson (2021-09-26 15:44:19)

SpaceNut · 2021-09-26 16:12:56

The transcript can be found at

https://www.justhaveathink.com/

The production of steel and cement accounts for about sixteen percent of all global greenhouse gas emissions.

A case where building with wood lowers emissions.

louis · 2021-09-26 18:05:59

Yes, it's the towers. Not the blades. And of course you still have to secure the base which does include concrete and steel I believe. One advantage of wood is that you can make bigger circumference towers without facing problems of transportation (steel towers come in complete sections where as the timber-based towers can be assembled from incomplete sections.

tahanson43206 wrote:

For all who've posted so far .... has anyone actually watched the video Louis showed?
I haven't yet, but definitely plan to do so.
My hope was that the towers were to be built of wood, rather than the blades.
A tower made of wood can be enclosed in fire resistant material.
However, a fire in the gear box could be a risk for any tower. Iron burns after all, but I admit ignition point is quite a bit higher than wood.
It seems to me an obvious solution is to design the gear boxes so that they stop automatically when temperature exceeds some reasonable limit.
I've never understood why the fires that occur occasionally in wind generators are allowed to happen.
Is someone trying to save a couple bucks? (or Euros?)....
Or is this just another example of sloppy engineering, to which every organization is prey?
(th)

louis · 2021-09-26 18:10:48

The claim in the video is that the wood-based towers are less susceptible to fire damage than steel. Sounds a but counterintuitive. But this is hewn timber, it's basically wood veneer sections not unlike how they made the Mosquito bombers. I don't think I've read anything to suggest they had a raised fire risk.

GW Johnson wrote:

I looked at it. That guy is quite interesting. Not far off the mark, actually. But, I stand by what I posted.
The fire risk has to do with the electrical hardware and the actual generating machinery. That stuff, if not detected in time, can blaze up. There is also the issue of lightning strikes (which ignite fires in combustible materials). If you build a wooden tower, you still must add something to ground it like a lightning rod. Otherwise, you increase the lightning strikes and the fires they cause.
Once you light off the wooden tower, you need a sprinkler system to put it out. Not just hold the line till the fire department can get there, literally put it out. Most fire departments would have no way to put out a fire in a combustible tower that tall. Same would be true of high-rise wooden buildings. (How inconvenient that I once worked in fire protection engineering, among so many other things.)
GW

kbd512 · 2021-09-26 21:47:15

This is merely another vain attempt to contend with the absurd over-consumption of raw materials masquerading as "green energy"- costing the consumer a lot of greenbacks while delivering very little energy. If the associated material consumption was not so problematic, then nobody would attempt this kind of silliness. In point of fact, it is so problematic that we're back to throwing stuff at the wall, hoping something will stick.

1. Wood has a strength-to-weight ratio inferior to CFRP, and certainly inferior stiffness. The material properties of wood are inconsistent, which means you need a greater safety margin to assure that the structure doesn't fail under load. You can make a structure larger in volume to increase stiffness, but then you need more wood, further increasing demand for a building material that's already in short supply. We can make any CFRP structure lighter than steel and concrete for a given strength / stiffness requirement. The real fundamental engineering reason skyscrapers are made from steel and concrete, as opposed to plastic coated wood and glue, is that it takes far more energy and labor, therefore money, to fabricate composites using either CFRP or plastic coated wood.

2. Wood lacks fire and water resistance. Fires will be far less of a problem than water intrusion, but any fire is guaranteed to destroy the structure, either outright during the fire or from water intrusion damage associated with putting out the fire.

3. Wood lacks resistance to biological agents like fungus or bacteria or termites that eat cellulose, especially over time. If you treat the wood with something that can realistically prevent that from happening for 20 years, then it's very toxic to basic cellular processes by definition and far less recyclable into new wind turbine towers, as well as being an environmental hazard for humans to contend with. Whereas bacteria have evolved to eat both plastics and diesel fuel in a mere 100 years, they've had hundreds of millions of years to evolve to eat cellulose. In this instance, they've elected to coat a laminated wooden composite structure with plastic, which means it's far more energy and resource-intensive than steel.

4. Trees take decades to grow. That process can't be "sped up" appreciably, but if it is, then the end result is wood with significantly less strength per unit weight and volume (the larger the individual growth rings, the weaker the natural composite becomes). Maybe some form of processed bamboo or hemp fiber would work, when infused with resin, but I see using wood for millions of skyscraper-sized structures as a technological dead end, and so did all other engineers on the planet, the moment steel and concrete became available in mass quantities. As with all other technologies, everything old is "new again", except that it's not, and some of this nonsense is getting pretty silly.

5. There is no global scalability to this solution, because it relies upon scarce natural materials fabricated using very stringent quality control, specifically because natural materials like wood are not homogeneous in nature. Again, I'd have an easier time believing that an abundant and rapid-growth plant fiber like bamboo or hemp could serve the purpose, accepting the limitations of natural composite structures. A single acre of hemp produces cellulose fiber tonnage equal to 4 to 5 acres of trees, except that the hemp can be harvested at least twice per year, if not three times per year in many tropical locations. It takes 90 to 120 days to grow 10 tons of hemp fiber per acre of land, so it's utterly impossible to grow trees of any quality fast enough to keep up with hemp or fast-growing bamboo, which yields 5 to 8 tons per acre. Pound-for-pound, hemp fiber composite is considerably stronger than high-strength steel, and 5 to 10 times stronger than wood.

I have a better question, though:

Why in the world would anyone revert back to using wood or natural fibers instead of using welding robots and jigs to turn coiled sheet steel, welded into a structure of suitable size, to make the wind turbine towers on-site, using commodity materials rather than highly specialized and expensive forged steel structures too large to transport via truck?

They make wind turbine towers out of a thick hot-forged steel tube, plate steel forged into a tube, essentially, because it's easiest to transport that to the wind turbine field. There's no reason why we can't make larger diameter, but lighter, sheet steel honeycomb structures that are welded together on-site. Metal aerospace structures are light yet stiff and strong by using good geometry for stiffness in conjunction with multiple thin pieces of sheet metal riveted or welded together. Why was that solution never considered, given that these things only last for 10 to 20 years before they're replaced? All these Modvion people have actually done is substitute much much thicker pieces of plastic coated wood for steel.

Sheet steel is also easy to cut and re-purpose or re-melt, so 10 to 20 years from now, when the turbine is defunct, a simple angle grinder or industrial tin snip can be used to deconstruct the tower, piece by piece. If the correct thickness of sheet steel was used, then a deconstructed wind turbine towers could then become the supply source for automotive sheet metal or liquid storage tanks. That solves the site cleanup problem, because people will recycle the material for free, in order to use it for other purposes to make money. There's no practical way to remove a 1 to 2 inch thick tube of steel for recycling, because you need a crane and a plasma torch to do it. Similarly, there's no practical use for a 2 inch to 6 inch thick multi-layer tube of plastic coated plywood or hemp / bamboo fiber. Seriously, what can you turn that into? A yearly global supply of knife handles from a singular tower? Why is every practical solution utterly ignored in favor of outright absurdity? SpaceX makes strong and light sheet metal structures by welding them on-site using commonly available and inexpensive coiled sheet steel, because when strength and temperature resistance matter, steel is the go-to material.

We're going to wind up living in a world with no trees left, no potable water, and no usable farmland, but hey we'll have "green energy", right?

"Just Have a Think" about that, because we're already seeing that happen. No solution is too nutty, so long as it feeds into the religion.

louis · 2021-09-27 05:26:34

1. The video indicates that steel is the main element in tower construction. So CFRP is not the right comparator - I think that's a bit of a red herring. I think the video is making the case that using wood you can build larger towers to support larger turbines. They claim this is because transportation on the road system is now an issue. I wasn't entirely convinced by that as presumably you could build you factory at a port. So I agree with your point that the "transportation" issue sounds a bit bogus.

2. I don't think we know whether the veneered wood will include fire retardant. All I can say is that the designers claim it will be more fire-safe than steel (in terms of structural damage).

3. My understanding from the video is that steel is also covered in a non-steel surface (presumably to protect it from salt air corrosion).

4 . There are over 3,000,000,000,000 trees in the world. There are 340,000 wind turbines. You can easily extract the required wood from forests without seriously affecting the overall ecosystems even if you need to make 30 million wind turbines. If it took 10 trees per turbine that would be 10,000th of the tree crop over a 25 year period. That sounds sustainable to me. Obviously it would be concentrated in areas where logging is allowed.

5. Bamboo does not survive well over decades owing to its cellular structure, unlike wood which, as we know, can survive well for centuries. We're talking about a minimum 25 year life for these towers which accords well with tree growth. Good production methods are practised in millions of factories around the world every day. That's a very poor argument against.

I am not saying that wood is the solution but it's about being open to solutions. I do think we (the taxpayer) should support innovative approaches to green energy because experience shows some of these technologies will be found to work well. I remain a little sceptical about the wood solution not least because steel is surely one of the easiest materials to recycle as you point out.

kbd512 wrote:

This is merely another vain attempt to contend with the absurd over-consumption of raw materials masquerading as "green energy"- costing the consumer a lot of greenbacks while delivering very little energy. If the associated material consumption was not so problematic, then nobody would attempt this kind of silliness. In point of fact, it is so problematic that we're back to throwing stuff at the wall, hoping something will stick.
1. Wood has a strength-to-weight ratio inferior to CFRP, and certainly inferior stiffness. The material properties of wood are inconsistent, which means you need a greater safety margin to assure that the structure doesn't fail under load. You can make a structure larger in volume to increase stiffness, but then you need more wood, further increasing demand for a building material that's already in short supply. We can make any CFRP structure lighter than steel and concrete for a given strength / stiffness requirement. The real fundamental engineering reason skyscrapers are made from steel and concrete, as opposed to plastic coated wood and glue, is that it takes far more energy and labor, therefore money, to fabricate composites using either CFRP or plastic coated wood.
2. Wood lacks fire and water resistance. Fires will be far less of a problem than water intrusion, but any fire is guaranteed to destroy the structure, either outright during the fire or from water intrusion damage associated with putting out the fire.
3. Wood lacks resistance to biological agents like fungus or bacteria or termites that eat cellulose, especially over time. If you treat the wood with something that can realistically prevent that from happening for 20 years, then it's very toxic to basic cellular processes by definition and far less recyclable into new wind turbine towers, as well as being an environmental hazard for humans to contend with. Whereas bacteria have evolved to eat both plastics and diesel fuel in a mere 100 years, they've had hundreds of millions of years to evolve to eat cellulose. In this instance, they've elected to coat a laminated wooden composite structure with plastic, which means it's far more energy and resource-intensive than steel.
4. Trees take decades to grow. That process can't be "sped up" appreciably, but if it is, then the end result is wood with significantly less strength per unit weight and volume (the larger the individual growth rings, the weaker the natural composite becomes). Maybe some form of processed bamboo or hemp fiber would work, when infused with resin, but I see using wood for millions of skyscraper-sized structures as a technological dead end, and so did all other engineers on the planet, the moment steel and concrete became available in mass quantities. As with all other technologies, everything old is "new again", except that it's not, and some of this nonsense is getting pretty silly.
5. There is no global scalability to this solution, because it relies upon scarce natural materials fabricated using very stringent quality control, specifically because natural materials like wood are not homogeneous in nature. Again, I'd have an easier time believing that an abundant and rapid-growth plant fiber like bamboo or hemp could serve the purpose, accepting the limitations of natural composite structures. A single acre of hemp produces cellulose fiber tonnage equal to 4 to 5 acres of trees, except that the hemp can be harvested at least twice per year, if not three times per year in many tropical locations. It takes 90 to 120 days to grow 10 tons of hemp fiber per acre of land, so it's utterly impossible to grow trees of any quality fast enough to keep up with hemp or fast-growing bamboo, which yields 5 to 8 tons per acre. Pound-for-pound, hemp fiber composite is considerably stronger than high-strength steel, and 5 to 10 times stronger than wood.
I have a better question, though:
Why in the world would anyone revert back to using wood or natural fibers instead of using welding robots and jigs to turn coiled sheet steel, welded into a structure of suitable size, to make the wind turbine towers on-site, using commodity materials rather than highly specialized and expensive forged steel structures too large to transport via truck?
They make wind turbine towers out of a thick hot-forged steel tube, plate steel forged into a tube, essentially, because it's easiest to transport that to the wind turbine field. There's no reason why we can't make larger diameter, but lighter, sheet steel honeycomb structures that are welded together on-site. Metal aerospace structures are light yet stiff and strong by using good geometry for stiffness in conjunction with multiple thin pieces of sheet metal riveted or welded together. Why was that solution never considered, given that these things only last for 10 to 20 years before they're replaced? All these Modvion people have actually done is substitute much much thicker pieces of plastic coated wood for steel.
Sheet steel is also easy to cut and re-purpose or re-melt, so 10 to 20 years from now, when the turbine is defunct, a simple angle grinder or industrial tin snip can be used to deconstruct the tower, piece by piece. If the correct thickness of sheet steel was used, then a deconstructed wind turbine towers could then become the supply source for automotive sheet metal or liquid storage tanks. That solves the site cleanup problem, because people will recycle the material for free, in order to use it for other purposes to make money. There's no practical way to remove a 1 to 2 inch thick tube of steel for recycling, because you need a crane and a plasma torch to do it. Similarly, there's no practical use for a 2 inch to 6 inch thick multi-layer tube of plastic coated plywood or hemp / bamboo fiber. Seriously, what can you turn that into? A yearly global supply of knife handles from a singular tower? Why is every practical solution utterly ignored in favor of outright absurdity? SpaceX makes strong and light sheet metal structures by welding them on-site using commonly available and inexpensive coiled sheet steel, because when strength and temperature resistance matter, steel is the go-to material.
We're going to wind up living in a world with no trees left, no potable water, and no usable farmland, but hey we'll have "green energy", right?
"Just Have a Think" about that, because we're already seeing that happen. No solution is too nutty, so long as it feeds into the religion.

tahanson43206 · 2021-09-27 06:53:04

For kbd512 re #10

There is too much in your post to comment upon every element, but one ** really ** jumped out at me.

Louis, I get the impression you do not understand why transportation of finished wind towers is a problem. I'd try to help, but I've learned you are impervious to input so will save my energy.

For kbd512 ... Elon Musk has been showing how to build tall steel towers on site!

Your description of building towers on site, instead of transporting the finished tower from the factory to the job site, ** really ** made sense to me, so it might well make sense to others.

Arguments against use of wood to make large durable structures seems amusing to me, in light of human history. Vast fleets of gigantic wooden vessels argue (silently but effectively) in favor of practical construction with wood.

All-in-all, I expect to see wood become a major structural element in future wind turbine designs.

However, at the same time, I think your idea of building the tower on site as SpaceX is doing with Starships makes so much sense surely someone other than yourself will think of it.

If someone who is already a member would be willing to report any developments along either of these lines, please do so.

If someone not already a member would like to help out, please read Post #2 of recruiting.

Bravo for a robust and productive discussion.

(th)

GW Johnson · 2021-09-27 14:11:20

The transportation thing is merely what oversize loads can you actually move down the highways. That sets the tower diameter: what will fit under bridges, power lines, and road signal structures.

The companies erecting these things already have the cranes that put the windmill power head atop the tower (and the blades to the power head). So, they just want to tip up a big tower as a one-piece tube, and bolt it to its foundation. Having to stick-build the thing on site costs more effort and money.

If the need ever becomes real for even-taller windmills, they will very likely ship the towers as two pieces, join them on site into a one-piece tube, and use the same cranes to tip it up and bolt it in place. They might have to beef up the bending strength with additional internal members, which is a problem for transport weight, but not transport diameter, as long as they stick with what fits under bridges.

There are some serious practical limits to how big these things can get. The blades are already hitting it, as are the current towers. These things are getting too long to make the turns on the road. The towers can be made into two or more shorter sections, but I have my doubts that one could really get away with blades that are not one piece from the factory.

GW

Last edited by GW Johnson (2021-09-27 14:12:26)

tahanson43206 · 2021-09-27 14:52:27

For GW Johnson re fabrication on site vs at a factory with shipping.

I think there is a tradeoff somewhere there.

SpaceX is showing that fabrication of very large steel structures "on site" is quite do-able.

I suppose it could be argued that the SpaceX facility is a factory of sorts.

Your suggestion of splitting towers in two lengthwise would certainly solve a big part of the bridge problem, but it wouldn't do anything about the curved roads problem.

The ** other ** solution that has not yet appeared in recent days on this forum is use of heavy lift lighter-than-air craft.

The British "Bums" vehicle is moving steadily forward (I get the impression)_but on the ** other ** hand, I've not seen any news indicating they are in commercial operation.

***
This topic was set up to celebrate the use of wood to make wind generator towers.

Any attempt to extol the virtue of steel (or any other metal) is beside the point.

** This ** topic is here for members to drop of reports of successful construction of towers (or any other large structure).

(th)

kbd512 · 2021-09-27 21:47:04

Louis,

louis wrote:

1. The video indicates that steel is the main element in tower construction. So CFRP is not the right comparator - I think that's a bit of a red herring. I think the video is making the case that using wood you can build larger towers to support larger turbines. They claim this is because transportation on the road system is now an issue. I wasn't entirely convinced by that as presumably you could build you factory at a port. So I agree with your point that the "transportation" issue sounds a bit bogus.

I disagree. Synthetic fiber composites are the correct basis for comparison with natural fiber composites, because that cuts right to the heart of any claims pertaining to weight reduction and improved fatigue resistance. If weight reduction and fatigue resistance were lacking due to the quantity or quality or geometry of steel tubing used, then the correct remedy was to either A- improve the stiffness of the structure with better parts geometry that reduces applied loads (from the wind) while decreasing material consumption (sheet metal aerospace structures), B- use a much stronger / stiffer / lighter synthetic fiber composite that's not subject to corrosion damage or rotting and is far less affected by moisture, or C- reduce the dynamic loads placed upon the structure by substituting a lighter nacelle (such as using Magnax's axial-flux PMMG, which is drastically lighter and smaller for a given level of output) and lighter blades fabricated from stronger / stiffer / lighter composites that require less material to achieve specified tensile strength and stiffness values. Those solutions are a "virtuous circle", as it applies to aerospace design.

The two man-made fibers, with highly consistent material properties, used in applications where both tensile strength and stiffness are important, are CFRP (high modulus Carbon Fiber) and GFRP (S2 Glass Fiber or "S-Glass"). The most common type of GFRP composites are made using "E-Glass" (so-called "Electrical Glass"), but that grade of glass fiber is neither as strong nor as stiff as S2 glass, nor CFRP. CFRP is actually weaker than S2 glass, when tensile strength is compared, but considerably stiffer.

Structures that need to be both light and strong and resilient are typically made from some combination of S-glass and CFRP. For example, wing spars in aircraft are fabricated from multi-layer BID or uni-directional fiber layups of CFRP or CFRP and GFRP (made with S-Glass), then vacuum bagged, and often cured in an autoclave at low temperatures.

Similar processes can be used for wing spars fabricated using multi-layer birch or poplar plywood laminates and epoxy resins. To my knowledge there are no species of wood nor plywood laminates that exhibit the strength-to-weight ratio / tensile strength / stiffness, of GFRP (made with S2-Glass).

A. Ultimate Tensile Strength only describes the load a material can withstand in tension before failure.
B. Yield Strength describes the load that can be applied prior to deformation, temporary or permanent.
C. Compression Strength describes the load a material can withstand in compression before failure.
D. Stiffness describes resistance to deformation or yielding under load.

If a structure yields (bends or deforms under load), that deformation is often accompanied by a progressive failure when it occurs while a significant load is applied (100% of the time, in the case of a large tower structure), in such a way that initially minor yielding leads to permanent deformation, followed by catastrophic failure. Yielding under heavy load generally leads to a condition where the tensile or compressive strength values for the material / structure in question are exceeded.

Basically, if you're going to forego the fabrication of a much cheaper and easier to form, solid tubular steel structure, then go for the gold and build something dramatically lighter and more durable, at the expense of increased materials and labor costs. Composite airframes that are built sufficiently strong to resist the aero loads placed upon them do not have set fatigue service life limits the way Aluminum airframes do. One of the very first certificated glass fiber composite aircraft, made when we were just starting to use such materials to carry aero loads, is now back in service, about 50 years later. Some Chinese entrepreneur paid for it, as some kind of experiment / proof of concept, and I think we discussed that here at one point. They checked the structures for voids and found none of significance, so they sanded off most of the old gel coat, applied new gel coat to protect the GFRP laminate from UV exposure, refurbished the engine and landing gear, and flew off the test hours to re-certify the airframe for flight.

The problem with the wind turbine blades is that they're frequently subjected to aero and gravitational loads that would fold up the strongest Titanium or composite fighter jet wing spars like empty beer cans. Over time, individual fibers in the laminate plies snap due to the crushing loads applied- repeated flexing of the composite structure, by design, to both reduce weight and cushion applied loads, ultimately resulting in "pull-out" of the fibers from within the resin matrix, which is rather interesting to watch, water intrudes after the gel coat is cracked, and then the structure is destroyed in short order if it's not repaired. Dependent upon severity, this can happen within mere seconds or it may happen over multiple years. Most manufacturing defects will be glaringly obvious in short order, though.

In general, wood is significantly less expensive than steel, except for aircraft grades of plywood and lumber. Commercial grades of plywood and lumber are seldom, if ever, acceptable for carrying significant loads (due to growth rings per inch, grain run-out, or grain orientation from cuts used to maximize production rather than the structural load carrying capability of the milled lumber). A wind turbine tower, much like a wind turbine blade, is an aerospace structure. A good 70% to 80% of what you'd likely find at the local lumber yard would be rejected outright. I went through dozens of 2x6x8 pine boards to obtain pieces that were minimally acceptable for making my non-standard entry way door, for example, and some of those were still warped or subsequently warped so badly after drying that I ultimately scrapped them, although I have a lifetime's supply of shim stock now. The labor to fabricate large wood structures with exacting dimensional tolerances is pretty much never cheaper than forged structural steel. It can take hundreds to thousands of hours to fabricate large structures, even with the aid of power tools. Since the tubes are pretty much identical in construction to modern wooden aircraft designs, it's not hard to imagine cost distribution- moderately cheaper materials, if supply is sufficient, but far more expensive labor and lots of it.

As a general rule of thumb, the cheapest light aircraft fabrication material is Aluminum sheet, due to its intrinsic material properties and versatility for making a wide variety of structures, from wing spars and skins to stiffeners. Sometimes it's used for landing gear legs as well, but getting both stiffness and tensile strength correct for the application is far more challenging than with tubular or flat steel spring stock- often times it's stronger than it needs to be if stiffness is appropriate, therefore almost the same weight as much cheaper tubular steel. That's why I asserted that low alloy coiled sheet steel would ultimately be the most cost effective and simple-to-fabricate, using modern welding equipment and fabrication jigs. Beyond that, the material is infinitely recyclable, even without melting it back down, so long as appropriate corrosion protection (simple urethane paint) is applied.

What I know with certainty is that wooden aircraft not kept in hangars can be ruined by water intrusion in as little as a year. These are mostly plywood construction, just like these towers, finished with varnish, a layer of glass fiber, and a gel coat. The same type of failure can occur for synthetic composites if they're not fabricated correctly or suffer from water intrusion due to a cracked gel coat. The only manner of construction technique used in certificated aircraft to not have airframe Airworthiness Directives (ADs) issued against them by the FAA, are made from appropriately welded (Argon shielding gas) tubular steel with good corrosion protection (primer and paint). Even then, any lapse in fabrication quality can lead to structural failure.

louis wrote:

2. I don't think we know whether the veneered wood will include fire retardant. All I can say is that the designers claim it will be more fire-safe than steel (in terms of structural damage).

I'd be far less concerned with the wood than the polymer coating on top of it, as it relates to fire retardancy. Much hay is made over this fact, but every steel tower wind turbine that's ever caught fire was subsequently destroyed or rendered inoperative. My money is on water destroying the structure long before fire does, and short of forest fires that burn everything, pretty much all of human history is on my side with this one.

louis wrote:

3. My understanding from the video is that steel is also covered in a non-steel surface (presumably to protect it from salt air corrosion).

Yes, paint or powder coat (a baked-on plastic coating), in most cases. All of these coatings eventually crack and expose the protected structure to the elements. Again, water is the problem. Wind turbines in deserts scarcely need any protective coatings on the tower, but one in the Pacific Northwest or New England would be trashed in a few short years. The most corrosion resistant type of coating for most metals is Cerakote (a ceramic-based coating).

louis wrote:

4 . There are over 3,000,000,000,000 trees in the world. There are 340,000 wind turbines. You can easily extract the required wood from forests without seriously affecting the overall ecosystems even if you need to make 30 million wind turbines. If it took 10 trees per turbine that would be 10,000th of the tree crop over a 25 year period. That sounds sustainable to me. Obviously it would be concentrated in areas where logging is allowed.

That's a rather meaningless statement in the context of appropriate source material for suitable grades of plywood and lumber. Pine is not an acceptable substitute for Sitka Spruce, for example. Douglas Fir is one of the closest analogs, though. The problem is that all of the material has to be repeatedly tested. Empirical methods are used to assure the integrity of wooden structures, to this very day. Teak may be highly water-resistant, but is also very prone to splitting, which is why it is used in thick timbers for sailing ships, with lots of tar / pitch to cover the splits, yet no wooden amphibious aircraft were constructed using Teak hulls, both because it was so difficult to bond and the aforementioned issue with splitting. It's almost as if all of this stuff has been tried before, repeatedly through the ages, but engineers have determined through hard-won empirical experience that there is such a thing as an appropriate versus inappropriate use for specific materials. We quit using wood for fabricating large structures due to the repeated structural failures and inability to easily predict impending failure.

Someone could've easily figured out the average lifespan of a wooden wind turbine tower some 25 years ago. The engineers moved past that type of structure in favor of steel, even though virtually all of the people who design these things are aerospace or architectural engineers with knowledge of natural and synthetic composites. There are trade-offs for every design.

louis wrote:

5. Bamboo does not survive well over decades owing to its cellular structure, unlike wood which, as we know, can survive well for centuries. We're talking about a minimum 25 year life for these towers which accords well with tree growth. Good production methods are practised in millions of factories around the world every day. That's a very poor argument against.

All of the wooden aerospace structures built a century ago are either preserved in climate-controlled museums or have rotted away. Whenever substantial quantities of water vapor are naturally present, wood will rot, and that describes virtually all of the places that have the best wind resources. There are wooden structures that have been continuously repaired over centuries, such as churches and a literal handful of historic homes, but that's about it. They're exceptions, rather than the rule. Pretty much every piece of USS Constitution has been replaced multiple times or drenched in epoxy, but even then it requires constant maintenance to remain afloat. While it's true that the lifespan of bamboo is not as great as wood, it's also true that bamboo grows far faster than timber and therefore several replacements over 25 years is far less problematic. That said, my emphasis was on the use of hemp fibers, which can last for at least several decades. Furthermore, any treated fiber appropriately bound in an epoxy resin matrix is not subject to biological decay.

louis wrote:

I am not saying that wood is the solution but it's about being open to solutions. I do think we (the taxpayer) should support innovative approaches to green energy because experience shows some of these technologies will be found to work well. I remain a little sceptical about the wood solution not least because steel is surely one of the easiest materials to recycle as you point out.

I think tax money should primarily support well-proven and reliable approaches to generating energy, irrespective of any faddish labels applied. At this point, nothing we're trying now is fundamentally new- not even the fusion experiments. Applied R&D projects that don't require non-existent or impractical technology also have my support. Humanity used wooden wind turbines for centuries. We stopped using wood for building large structures when high quality steel became available in large quantities and machine tools replaced hand tools in industrialized manufacturing and construction. The robotic welding and cutting technology available today virtually assures that any wooden structure of equivalent strength will take far more time and labor to fabricate, for no practical benefit.

I don't think this is a practical application of wooden construction, and definitely not at global scale. Should we conduct an experiment with a small field of wind turbines? Sure. If it doesn't work, though, no excuses, simply admit that it doesn't work the way we want it to and move on to the next potential solution, rather than cutting down entire forests in a vain attempt to combat the weather. No modern cargo ships or aircraft are constructed from wood, and there are multiple excellent reasons for that.

kbd512 · 2021-09-27 22:05:51

tahanson43206,

Balsa wood is still used in the cores of wind turbine blades, as part of a "sandwich core" construction combined with GFRP or CFRP, since the composite skins carry most of the tensile loads. By doubling the thickness of a section of material, you can increase the stiffness / resistance to deformation by a factor of 8. If the core material is comparatively light, then you can create a stiff and strong yet lightweight structure. If we were going to use something like pine plywood or lumber as a core material with GFRP skins, then I could see this being a bit more practical. Wooden yachts are constructed that way, for example. However, Modovion / Modvion / whatever they're called is simply fabricating a very thick laminated plywood tube, substantially increasing the sectional thickness of the structure to account for the different strength and stiffness properties of plywood, as compared to steel. That will work, so far as carrying the load is concerned, but again, ultimate durability is the big question mark. Build several full scale towers to see how long they last. We should have a good empirical baseline in 10 years or so.

tahanson43206 · 2021-09-28 06:51:39

For kbd512 re #16

Thanks for your addition to the topic! The use of balsa wood to add lightweight stiffening to wind turbines is new to me, and perhaps other forum readers will appreciate the insight as well.

I ** think ** Louis original concept for this topic was construction of towers, but GW Johnson extended the topic to include blades, and your addition of balsa is a confirmation that (some) wood may well have a future in wind blade construction.

***
This next is pure speculation on my part, but it seems (to me at least) perfectly reasonable to suppose large wind turbine blades could be fabricated using 3D printing. The exterior is probably wrapped in fiberglas(r), so I asked Google for help with that question:

The sum of the glimpses from the set of quotes below is that currently blades are made with fiberglass and balsa wood, but apparently GE is developing a fabric to replace fiberglass...

[PDF] Manufacturing a 9-Meter Thermoplastic Composite Wind Turbine ...
www.nrel.gov › docs
Currently, wind turbine blades are manufactured from a combination of glass ... Next, a layer of veil fabric, the fiberglass layers, spar caps, ...
Using of Composite Material in Wind Turbine Blades - Science Alert
scialert.net › fulltext
Rotor blades are manufactured from composite materials using fibreglass and polyester or fibreglass and epoxy, sometimes in combination with wood and carbon.
How New Wind Turbines Produce Far More Energy - WSJ
www.wsj.com › articles › wind-turbine-renewable-energy-11620848318
May 16, 2021 · Early wind-turbine blades were made from fiberglass and resin. The materials limited their size and thus their power output. Fiberglass. 2021.
Wind Turbine Blades Don't Have To End Up In Landfills - Union of ...
blog.ucsusa.org › james-gignac › wind-turbine-blades-recycling
Oct 30, 2020 · This happens through the turning of large fiberglass blades, which then spin a generator to produce electricity. Wind turbines, as they are ...
Missing: wrapped | Must include:wrapped
Fabric-Covered Blades Could Make Wind Turbines Cheaper & More ...
scitechdaily.com › fabric-covered-blades-could-make-wind-turbines-cheap...
Nov 30, 2012 · GE's latest wind technology development is fabric-covered wind turbine blades, which are supposed to even more efficient that the fiberglass ...
A Look Inside A Factory For Giant Wind Turbine Blades | GE News
www.ge.com › news › reports › towering-achievement-look-inside-factory...
Jun 11, 2018 · To grossly simplify, workers make the blades from a “sandwich” of fiberglass fabric and balsa wood. They lay out the material, which resembles a ...

I think my suggestion of making the core of wind turbine blades with 3D printing would hold up to further study.

Earlier in this topic, GW Johnson brought up the difficulty of transporting large objects from factory to job site.

It would seem reasonable to me to set up the factory right at the job site, if the job site is large enough.

That way nothing large has to be transported to the job site.

The factory could even be self-sustaining, as soon as the first wind generators are operating.

(th)

kbd512 · 2021-09-28 08:02:42

tahanson43206,

We already have fiber tape laying machines, and most modern wide body airliners are produced that way (Carbon Fiber tape wrapped around a mandrel or mold). I'm not sure what 3D printing would add to the blade fabrication process, since it wouldn't speed it up and wouldn't produce a stronger or more durable product. Unidirectional fiber tape (sometimes referred to as tow or roving), is pretty much the strongest stuff that money can buy, happens to be less expensive than pretty much any woven fabric, and the lightest possible construction for a given strength, after it's been bagged and autoclaved. The strongest / lightest practical tower structure could be fabricated the same way, producing a structure considerably lighter than steel for a given strength and stiffness. Large molds are very expensive, but for the number of flawless copies that must be produced, totally worth the money spent on them.

tahanson43206 · 2021-09-28 08:44:04

For kbd512 re #18

Thanks for picking up on the 3D Printer suggestion.

The interior of a wind turbine (according to your post earlier, and the Google collection cited subsequently) is made of balsa wood.

The need (as I understand it) is to have a very light weight but very strong (not compressible) interior, so that the appropriate fabric/fiber can be wrapped around it.

There is a limited supply of balsa wood, so it would seem reasonable (to me at least) to look for a substitute.

The distinct advantage of the 3D Printer approach is that once the desired shape is computed (by designers with airfoil training), as many identical blade interiors as may be needed can be fabricated.

It certainly doesn't matter that the 3D Printer will take a long time, because you (er, the entrepreneur) can put as many of them into service as the manufacturer of 3D Printers can supply.

You (er, the entrepreneur) can then use relatively unskilled labor (under close supervision of course) to wrap the shape in whatever material makes sense.

Edit: A tape wrapping machine is even better, but the employee will have a higher level of skill, but need less supervision.

Large molds are nice, but they are likely best set up at a manufacturing facility where they can be used over and over again to make the copies you descibed. However, you (er, the entrepreneur) must then transport the blades to the job site.

The original article that Louis quoted to start this topic pointed out the competitive advantage of wood for tower construction due to its greater suitability for transport to the job site in sections that can then be assembled.

What I ** hope ** will happen with this topic is that members with posting privileges will keep a watch for news about wood being used to make wind turbine towers, and will post anything they find here, to add to the collection of useful/interesting information.

Edit at 13:19 local time, after kbd512's next post.

The concept I have in mind for 3D printing appears to be somewhat different from that of kbd512.

It may not be well known to those who do not have or work with 3D printers, but it is not just common, but ** normal ** for the interior of a shape designed to be printed on a 3D Printer to be filled with a honeycomb that is specified by the operator at print time.

The range of density of the honeycomb can be specified from 100% (no gaps at all) to some lower value. The exact lower value is not familiar enough to me to be sure, but it ** could ** theoretically be zero, which would mean there would be NO filling at all.

The actual normal range is less that 100%.

The result is that a shape is created that is strong because the cells of the honeycomb are cubical, hexagonal or triangular, for even greater strength.

A turbine blade 3D Printed as described would then be a complete form upon which the exterior skin (eg, tape) would be laid.

(th)

kbd512 · 2021-09-28 09:53:30

tahanson43206,

The answer to your question is closed cell foam. The real reason natural materials have fallen out of favor is limited availability of high quality stock and synthetic materials with superior material properties.

Again, if you have a mold, then dimensions can be more precisely controlled than with 3D printing. The idea is to tightly wrap fiber around a mold / mandrel, vacuum bag it, autoclave it, pull it out, check for defects, fix any defects found, then bond the foam around the inner skin, then repeat the first parts of that process for the outer skin.

It's not practical to fabricate large blades without lots of other specialized tooling, so again, 3D printers don't add much to the equation. To achieve the precision required, the 3D printer will be gantry mounted, it will still have to affix the printed material to a support structure during manufacturing (a mold), and then the material still needs to be cured in a large autoclave.

Whether the machine is wrapping tape around a mold or printing around a mold, a skilled operator is still required, not because feeding materials to either machine is all that difficult, but because they need to identify any defects during the fabrication operation. That's why you'll see tape laying operators periodically stop and check the work piece. They want to assure that the tape is laid flat, no air pockets, etc.

If maximum throughput was desired, then you'd use the "Carbon Forging" technique that uses high heat and pressure for a very short period of time to instantly (well, within mere seconds) infuse with resin / cure the fabricated parts. They will use chop or recycled scrap fiber, which is even cheaper than tow / roving, in those processes in order to save money. The parts produced that way are still nearly as strong / stiff / light as laborious fabric layup / bagging / autoclaving- even using the absolute cheapest material that money can buy. If it takes all day to lay tape, yet the resin infusing process takes seconds, then one tape laying machine and one forging press can produce 1 blade per day, rather than 1 per week using traditional methods. You'd need a head count of 6 people to produce the complete set of blades for a single wind turbine per day. You need an Invar or Kovar dies / molds, which are very expensive, but then you get a lifetime supply of zero-defect parts using scrap materials or low cost non-woven fiber, so the marginal cost to produce the next part is exceptionally low, as compared to other fabrication methods.

Calliban · 2021-09-30 16:50:26

Louis's idea is a good one in this instance, although the applications are limited to relatively small machines. But such things do have their place. Given the current energy crisis and peak everything bubble, we may need to have contingency plans for a situation where we need to carry society on without fossil fuels and without fusion or large scale nuclear power. Life gets a lot poorer, more basic and a lot more Amish.

Traditionally, windmill towers were made from brick or stone, sometimes wood. Masonry isn't a perfect solution, because they need to be quite squat to absorb all loads compressively. And the squat tower creates turbulence that effects efficiency. But they lasted for centuries and have low embodied energy. The structures were often either habitations, or contained machinery. So the tower served a dual function. The Dutch used windmills for all sorts of things. Grinding grain, sawing wood, milling for paper, driving bellows, pumping water, etc. The sails got replaced, but there are windmill towers in England and the Netherlands, that date back to the seventeenth century. There are wooden towers that are quite old as well. It is not a bad idea, by any means, to construct small to medium sized turbines using wood, brick and stone today. Such things have niche applications. Nothing has to be the answer to everything. A stone tower was and is something that can be built locally by local masons and builders. The same with wooden blades or sails.

Wood was used for sails. The size of windmill sails is limited by the largest trees available for the sail booms. A modern turbine could use carved wood for relatively small machines or wood based composites. Centrifugal stresses limit the maximum diameter that a wooden bladed turbine can reach. Machines using wooden blades are probably going to be limited to 100s kW power levels, not MW. So there are compromises to be made. But wood is a naturally available biomaterial. It has low embodied energy and it can be grown. There is no reason why wooden blades cannot be appropriately shaped within size limitations.

I once attempted to design a workshop that used direct mechanical wind power to drive equipment using a line shaft. The thing that made it attractive, was that I could build a purely mechanical device easily myself. Just a tower, the vertical axis wind turbine, along with gears, phosphor bronze bearings and a shaft running through the workshop. I could adjust workload and tasks with the wind and could use excess wind energy to generate heat by fluid friction for my house. Whilst it would have worked in principle, there are obviously a lot of problems going against it. It would have meant working with the wind. Doing 18 hour days in windy times and taking time off during calm periods, like the summer. A bigger problem was that most machines are electrical- either 240v or 440 3-phase. Trying to modify machines to accept a mechanical input was a pain in the arse and power transmission with belts and gears would have required constant maintenance. So I gave up, limited my ambitions and now have a 240v, single phase wood and metal workshop. It does most of what I need.

There are applications where small wind turbines, generating tens to hundreds kW power could be useful. Electric power is most versatile. But there are situations where direct mechanical shafts power is useful, things like pumping water or milling. I can remember reading about an Amish gentleman who coupled a wind turbine to a piston compressor and used the compressed air to power a workshop. I thought that was cool. I often wonder if there are innovative ways of directly coupling electrical farm equipment, for high power things like ploughing, planting, spraying and harvesting, to a wind turbine, allowing direct electric power to supply everything without batteries. There probably are. I like the idea. One way might be to have an overhead cable, with alternating sections of +VE and -VE DC at perhaps 440V. As the tractor advances up the field, sliding, hanging contacts run along the cable. A rectifier keeps current running the same way through the motor as the phases switch over. The cable stretchs between two poles, which are mounted on wheels and can be pushed manually along the field as the tractor or harvester moves along. The alternative is to make the fields circular and have the electric contact on an arm that swings around the centre and is supported on a wheel at the outside. You set it on the pole at the middle of the field before you start. It would only work for small fields.

One thing to keep in mind, is that there is always the possibility that the shit really does hit the fan, fossil fuel depletion and financial mismanagement cause a great depression and society slips down to more primative levels. We would need to build systems that are simpler, which meet our needs. I cannot build a nuclear reactor in my workshop. But a wind turbine capable of generating a few tens of kW of mechanical or electrical power, is something I can do for myself with relatively simple materials. It is not an efficient way of powering a complex, high income society with high energy needs. But wind power does provide a way of harnessing mechanical energy using simple though bulky systems, that you can build yourself. I can build the tower from stone, rubble, wood or even rammed earth. Sails can be made from wood or maybe molded polyethylene from plastic waste. A mechanical system that operates simple machinery is something I can do myself. Likewise, with a DC generator. When the wind is high, equipment runs fast. When it is low, equipment runs slower. You adjust your workload according to supply. No storage needed. Very simple and very long lasting.

I looked into the possibility a while back of transporting freight through a pipeline or through ditches using wind power. Freight would be loaded into steel, plastic or wooden cylindrical containers, which are ballasted to have the same density as water. These are injected into pipelines, probably cast concrete or ditches if we can't make pipelines. Along the pipeline or ditch, wind turbines would take off overflow and inject water, pushing the capsules along at a few m/s. Using a series of pipelines, terminating at junction ponds outside of major towns and cities, it would be possible to transport freight from anywhere to anywhere in the UK with a few days using the directly coupled mechanical power of the wind. The wind pumps would be simple centrifugal pumps, coupled directly to the steel or wooden rotating shafts at the bottom of the tower. The tower would be stone; the sails would be wood. Low embodied energy and easy to make and repair.
They should last for centuries. Only the bearings and gears need to be steel. If the worst comes to the worst and the UK begins to lose access to oil supplies, I feel confident that this is a system that I could build and make work, given sufficient labour. It would be slow compared to trucks, but could transport just as much tonnage, using a tiny fraction of the energy - all direct mechanical wind power. We may need things like this. What is headed our way may make the Great depression look tame in comparison.

What other things could we do with wind, solar heat and a little biomass? We could cook using the wind and biomass. Sunshine in the summer. The most efficient way of cooking with wind is resistance heaters, using AC current. However, a simpler system could use directly coupled mechanical power, generating heat through mechanical resistance in vegetable oil. This could be heated to up to 200°C and used to heat centralised ovens and cooking facilities. This is a centralised solution. A town could cook in this way. A number of smaller businesses, restaurants, bakers, community kitchens, laundries, etc, would be built around the centralised heat source. Steel could be recycled using electric furnaces. We wouldn't need to reduce any new metal for a while. Cars would provide a source of raw steel for decades. Water will be provided by digging wells and using the wind to pump water into covered storage ponds.

Again, hopefully we won't be reduced to such pre-industrial ways of living. But it is never a bad idea to think about how we would do things if life really takes a bad turn.

Last edited by Calliban (2021-09-30 18:29:04)

kbd512 · 2021-10-01 18:28:32

Calliban,

Wood isn't nearly as stiff as CFRP or GFRP, so a wooden blade would weigh at least double, if not triple as much as a synthetic composite blade, and then it requires a much stronger tower to support the much heavier blades. Yes, we would use wooden composites to increase the length of the blades, probably in conjunction with CFRP spars and/or spar caps to carry loads and provide adequate stiffness.

tahanson43206 · 2021-10-01 19:20:49

With a nod to kbd512 for #22 and advocacy of composite materials over natural wood ...

For Calliban re #21

That post was a classic (is a classic) (in my view anyway) ... Thanks for the glimpse of your exploration of "natural" living.

Coming from Dr. Dartnell's Knowledge Forum (as I do) I am struck by how well your post would fit into the survival oriented themes there.

Since ** this ** is the NewMars forum, I am challenged to think of tags that would work for the forum audience ...

SearchTerm:Survival using wind power for mechanical systems and home heating by friction heating.

If anyone else can think of a tag that would work for them, please add it to this topic.

(th)

SpaceNut · 2021-10-01 20:16:15

The old skills of a museum piece is what we need to view and then we use imaginative thinking to transform the device into what we need.
Things that spin slowly most of the time are of large diameter while to transform that low rpm we use a ratio of a large pulley to a smaller one to get more rpm's at the smaller one. Thats how we make a ten speed work when pedaling.

The real trick is to take the energy which is mechanically create and store it for future use.

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Wood is Good for Wind

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