The blocking effect is of particular interest to AWE, as we are not so close to utilizing the Betz’ limit
Dabiri’s work is documented on Betz's law: validity and limits. And also the paper in reference on Betz limit and power available in the wind mentions the known Betz’ limit of 16/27 for drag systems, and 4/27 for yoyo systems.
In my opinion a AWE-farm should not be arranged like a current wind-farm, but could share a frontal airspace. with several floors for several unities (a single gigantic kite would be desirable but not possible), avoiding both blockage and a too large space use.
Sad to see this ongoing pretense of being in position to maximize Betz, when nobody has even a truly workable system. Like worrying about how to get a car waxed and shiny when it hasn’t even been designed yet, let alone built. "Dabiri was (is?) a crackpot. Like someone claiming steam-powered 3-wheeled go-karts could reduce freeway congestion. Huh? Sure, reduce windspeeds at windfarms by installing junior-sized models of the type of wind turbine nobody wants to bother with. Sure Dabiri… Never discussing why they didn’t choose regular turbines… The only people discussing Dabiri are people who don’t know anything about wind energy. That’s it. You wanna be flagged as one more “crackpot”? Spend all day talking about Dabiri.
Dabiri’s purpose is the optimization of a whole wind-farm, not VAWT as such even though he experimented them. Now, he studies HAWT by “pointing turbines slightly away from oncoming wind”.
Maximizing Betz leads to maximizing the power/space use ratio. A “truly workable system” producing 1 MW by taking 3 km² land will never be bought. So maximizing Betz is a part of a “truly workable system”.
If Dabiri was so smart, he would not have wasted the time on vertical-axis turbines.
And if people here were so smart they wouldn’t waste their time humoring “Desperate Dabiri”. Maybe next he’ll be presenting proper placement of turbines, as though that is his own idea too. My take is Dabiri should “get a job”. To me it is alarming that so many peoples’ “work” these days amounts to doing nothing, producing nothing, just pretending.
The point here is that a HAWT park will experience an x% reduction in windspeed because they are extracting much of the available energy. AWE doesnt currently extract a lot of power, and it may seem that this would mean AWE will not see the x% reduction.
So while it’s not produced energy as we would all like to announce (but we are unable to), at least this is probably good news to the concept AWE
Hi Tallakt:
I think any wind energy technology will face the same or similar issues whenever the density or repetition of the apparatus in the direction of the wind increases. And I think Pierre has a point that space needs to be efficiently utilized. Of course. Like it always has in wind energy, unless you have just a single installation. But I also think, after 12 years of reading this kind of hand-wringing stuff, such details make no difference if nobody is demonstrating an economical wind energy solution.
Here is a news article that has been really king the rounds for the last week or so:
No. This should be a clear win for AWE. AWE could use wind at higher altitudes thus reducing the effect of blocking and wakes.
That is - for the same produced power using the same land area, AWE will probably experience less blockage as it’s extracting a lesser fraction of the power from a larger area.
This effect may be separated from other effects, such as the problem og achieving low cost, power density per area, safety etc.
And it’s probably not a very big effect. But it seems this could favor AWE by 0-5% (numbers being taken out of thin air based on my guesswork).
Yes that was the same thought I had. Part of the problem is these offshore turbines are all at the same level. And no fresh wind can come in and mix from below. So it favors AWE. But still, that’s just one more minor detail. We started with “overwhelming” advantages:
Many times the windspeed, deploying in the jet stream, minimal structure, etc. But then we encountered tether weight and drag, thinner air, probable icing, launch and handling difficulties, lack of operational expertise, unknown airborne windfarm layout due to unknown airborne windfarm technology, regular wind energy costs dropping in half, etc., etc.and mainly lack of a proven effective airborne technology for lowering the cost of wind energy. It’s like trying to fine-tune your rows when mowing lawns, when you don’t have a decent lawnmower to even use - in the face of existing lawnmowers that do work fairly well…
There have always been “overwhelming advantages” for AWE, the question is what to do about it.
Can an answer to this question be guessed at by equating the (AWE) wind park to a windbreak? Or is that too different to be useful?
You would change the porousness and height (geometry) of the windbreak in your simulation and see what difference it makes.
1 Like
Yes, all surface roughness has analytically comparable effects on the wind field, slowing velocity through vegetation, terrain, buildings, and/or wind farms. When flow is not dammed by overly large obstacles, an accelerated LLJ (low-level-jet) layer forms just above surface roughness. LLJs also commonly form late at night over cold-air surface inversion.
LLJs are thus a prime target for AWES harvesting, as one must go considerably higher to reach any faster wind. LLJs are the nice “bump” in global wind gradient plots, commonly peaking at about 500m high. Wayne German first identified LLJs for AWE and Cristina Archer wrote a scholarly overview for the 1st Springer AWE textbook.
“Betz” is such a tired useless crude engineering approximation, neglecting countless higher-order AWES factors, and too often troll-bait in erstwhile advanced wind discussions. Betz was a Nazi who did not even originate the misleading and obsolete concept named after him. “Blockage” is also an easy design issue to put to rest: Don’t block flow into a WECS, its parasitic. Same with “wake effects”; avoid wakes.