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Michael Dowling

(1)

I find it incredible when I read that a 60m plastic composite blade weighs 17 tonnes! 1700 kg, yes, but 17 tonnes! I can see how old blades would be a recycling problem.

H

(2)

Do you know this type of wind turbine?
http://www.eolienne-a-depression.fr/index.php?option=com_content&view=article&id=54&Itemid=54

Kris De Decker

(3)

@ H

No, never heard of it. Very interesting, thanks !

Troy Parker

(4)

Aircraft wings are made from aluminium, which is indeed energy-intensive to make, but recyclable. Perhaps this could be a suitable material for turbine blades.

L

(5)

Thanks again for another great article.
However, having read the term solid wood, I had to comment that laminated veneer lumber has a substantial amount (up to 8 %) of phenol formaldehyde resin holding it together. As is the case with cross laminated timber (CLT, which has a smaller content of 1 % of polyurethane glue), it often gets called solid wood although it's completey reliant on plastic.

Kris De Decker

(6)

@ L

I'm aware of that, but the number I found for laminated veneer lumber was 2% glue. That's very little compared to the resin content in wood or glass fiber composites, so I found it not really an issue. If you cut a discarded wood blade into pieces, you still have very useful material to do something else with, even if it has some plastic in between the layers.

Nevertheless, if you have more information, feel free to send it along. And if this means that we should go back to the blade design from 1959, I am also OK with that.

L

(7)

@Kris

Thanks for your reply. I'll PM you about the glue content. My concern had to do with 1) when the glued wood is left to decompose and 2) being reliant on the industry that makes the glue. Going for the designs that didn't yet incroporate glue or other problematic chemical compounds gets my vote. You said it best: "If we would reduce energy demand, smaller and less efficient wind turbines would not be a problem."

Kris De Decker

(8)

@ L

Great, thanks. During my research I found a paper that describes a low-tech production method for making laminated veneer bamboo using hand tools, screw-driven mechanical presses, and widely available, economical adhesives.

Mahdavi M, Clouston P, Arwade S. 2012. “A Low-technology Approach toward Development of Laminated Bamboo Lumber”, Elsevier: Construction and Building Materials, Vol. 29, pp. 257–262

Petersen

(9)

Hi I am looking for blueprints to build a small wooden wind turbine for the uses of a school in a developing country. Thank you very much

Kris De Decker

(10)

@ Petersen

Check Hugh Piggott's design in the other article: https://www.lowtechmagazine.com/2019/06/small-wooden-wind-turbines.html

ijk_ijk

(11)

Thanks for your very preciosus article as usual. Just a question: why a composite plastic o carbon blade can't stand forever? Why they have a so short life? If we can extend the life o these blades to many decades or centuries whe can have a more suistanable wind power.

Kris De Decker

(12)

@ ijk-ijk

That's a very good question. It was calculated that the first fiberglass blades from the late 1970s had a life expectancy of 70 years. (And the same was true for the wood-alu blades from the Gedser turbine). The reason was that engineers did not fully understand all the forces that act on a wind turbine blade, and thus built them as strong and durable as they could.

This suggests that the limited life expectancy of today's wind turbine blades is intentional. I assume that this brings cost advantages, but at the expense of sustainability. So indeed another route to lower the environmental impact of wind power would be to build plastic blades stronger again.

Mathew

(13)

Alternatively, we could further develop kite wind power, which is an almost entirely fiber-based system with power generation on the ground. Ground-based power generation helps limit the need for rare earth materials or other lightweight, high embodied energy components.

A commercial system is being spun off by TU Delft:
https://kitepower.nl/tech/

Google is also funding a much worse (sustainabilty-wise) system with Makani power. They are generating power on the kite and sending it down a custom conductor cable.

Both systems result in dramatic material savings, and could have synthetic materials substituted for natural fibers. The soft fabric kites' polyester fabric could easily be replaced with silk without any performance loss.

A stiff cable that transmits mechanical power would be more difficult to make from natural fibers, as their elasticity results in losses. Steel wire could work, but at a significant performance and safety disadvantage.

Boris Doderer

(14)

@Kris and ijk-ijk

The problem with forever lasting plastic materials in this kind of application is not just the forces acting on a blade. To a great extend the plastic material is affected by sun radiation (infrared, say: heat as well as ultraviolet), cold, rain and frost. The radiation - especially ultraviolet - will weaken the material's surface, which will - in combination tith the bending by the wind force - eventually cause microscopic damages. We don't need to talk about the consequences of cracks in the presence of water or moisture and frost.
Furthermore the whole design of a blade is a material composite, the materials having different reactions to the environmental impacts mentioned above. There are plastics that absorb water, causing swelling of the material, and some that don't. Plastics in general have a greater expansion coefficient than metal, while the one of glass (fibre) is often much lower. Now imagine the temperature difference of e. g. -20 to +40 °C over one year. Even very fine tuned material compositions are not perfect under these circumstances.
All these factors put together are quite limiting for the lifetime expectancy of a wind turbine blade.
You usually care for the surface of your cars' coatings (washing, polishing, etc.). I live in an area where we have three turbines in close proximity, and many in visible distance. I've never seen them being polished or re-painted. only one of them seems to be maintained frequently, the others just work. Do this to your car, and see about the longterm outcome of it.

F Pierot

(15)

@H, about depression windmill (éolienne à dépression):
Intesting and very simple concept - although with a rotating airtight bearing (!?).

I'm curious of the efficiency of the equipment, as using variable pressure gases is usually destroying the efficiency (problems of heat transfer whiled compressed uncompressed).

Christian A Lysholm

(16)

Any examples of weight or volume loss of material from turbine wings?

When the output effect is reduced by 26% a lot of material has eroded. How much?

Darkest Yorkshire

(17)

According to these -

https://www.renewableenergyworld.com/articles/print/special-supplement-wind-technology/volume-1/issue-3/wind-power/wind-farms-adapt-to-forest-conditions.html

https://www.uka-gruppe.de/en/landowners/forest-wind-energy/

only the larger turbines are suitable for forest wind farms, to keep the blades high enough above the canopy. Smaller ones need to be in a more open area (or natural funnel) to keep the air flowing smooth and fast.

Darkest Yorkshire

(18)

If you're using wind power to directly run air compressors, what size of windmill would correspond to what air pressure? Different kinds of pneumatic tools and machines require very different pressures, and some of the industrial compressors are monsters. Following on from that, what's the largest vehicle that could be powered by compressed air? I've seen forklift trucks and similar sized vehicles -

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

https://www.forkliftaction.com/news/Future-forklifts-powered-by-compressed-air-9321.aspx

http://www.engineair.com.au/

They could have a massive future in industry, powered by wind and hydro compressed air.

But what about tractors? Since most wind and hydro power is out in the countryside, the 25 kilometres a compressed air network can reach could be connected to farms. According to compressed air equipment manufacturers, nearly any piece of equipment on a farm can be run pneumatically. If that could extend to the tractor and any other mobile equipment, it would solve a lot of problems and let farms run more independently of electricity and fuel, without the problems of using draught animals (feed vs food, limited versatility).

Jasper den Ouden

(19)

What about titanium? It can be re-used as a metal, and doesn't have metal fatigue issues.

Often wonder why titanium isn't a more popular metal. Darpa(presumed imperialists) wanted to popularize it one point.

A

(20)

@Jasper

It's a great material, but very difficult to machine/form. Cost per kilo is also dozens of times higher than alu/steel (although obviously you'll be using less kgs!), so it's a material that really requires strong justification to use.

The two largest suppliers in the world are China & Russia, so there's also traditionally been strategic issues with relying on Ti production.

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