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Forum Index : Windmills : Storing The Wind

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MacGyver

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Joined: 12/05/2009
Location: United States
Posts: 1329
Posted: 03:14pm 24 Apr 2014
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Crew

I know I hold an unpopular view of how to store wind power, but I'm "Friends" on FaceBook with Nail and today he posted pictures of his axial-flux machine torn apart by weather and usage.

This is EXACTLY why I like the idea of using the windmill to pump air down to the ground, to be stored in a receiver and metered through a small air-driven engine coupled to an alternator DOWN ON THE GROUND!

Okay, I'm old(er), that's a given and you're never going to catch me up a tower with a wrench in my teeth trying to fix anything, but the fact that although all this high-speed operation creating electricity up there in the wind and rain works, to me at least, doesn't warrant all the problems it creates.

I know converting wind to compressed air and then into kinetic energy ON THE GROUND is not very efficient, but at least it's way simpler. After all, the only thing up top is a set of blades driving a swash-plate transmission driving a small air pump. Over-speeding is not a problem and the mill head can be locked down in storms by merely shutting off the output air valve DOWN ON THE GROUND when things get out of hand. The mill will turn a bit, but once it reaches a certain point, it can't overcome the pressure-head load and it stops; eazy-peazy!

Anyway, that's my two-cents' worth. I hope Nail gets things back up and running soon.


. . . . . MacEdited by MacGyver 2014-04-26
Nothing difficult is ever easy!
Perhaps better stated in the words of Morgan Freeman,
"Where there is no struggle, there is no progress!"
Copeville, Texas
 
powerednut

Senior Member

Joined: 09/12/2009
Location: Australia
Posts: 221
Posted: 09:23pm 29 Apr 2014
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Personally I'm a bit of a fan of the concept, and I'd like to see some details of some of your machines when you get a chance.

To me it strikes me as a way to store energy in a way that is readily re-used, without concerns over reducing the lifespan of the storage by use a bunch all at once.
 
Madness

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Joined: 08/10/2011
Location: Australia
Posts: 2425
Posted: 10:30pm 29 Apr 2014
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Would you expect the compressor to hold in severe storm conditions? Given how much the energy in the wind increases enormously your compressor could be developing some very high pressure unless it sh*ts itself first.
There are only 10 types of people in the world: those who understand binary, and those who don't.
 
MacGyver

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Joined: 12/05/2009
Location: United States
Posts: 1329
Posted: 02:03am 30 Apr 2014
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Madness

Conceptually, I'd agree, but the reality is it just doesn't happen. My compressor is basically a bicycle hand pump that has been re-purposed. It'll withstand probably a couple hundred pounds before it explodes, but it would take a ginormous moment arm (read that blade length) to develop that much force and my blades are usually 24". Remember me? I'm the guy, who builds little stuff.

My receiver's pressure lift-off safety valve is set to somewhere around 45 psig! I run all my little air engines off low pressure. If I want more power, I increase the bore or stroke.

Even if the blades were long enough to develop the kind of pressure in the pump to destroy it, think of this: Your family car has perhaps hundreds of horsepower, right? Try edging up to a concrete wall, so the bumper touches it, then pour on the coal. How far did the car move against the stationary wall? See what I mean?

When the weather turns nasty, although in Texas it can do so in no time at all, the output valve is closed, so a pressure head develops slowly and it's just like the car pushing against a concrete wall. Even if it were to breech the pump, the blades are made of Coroflute plastic on a hollow-aluminum spar, anchored to the hub with steel screws. If they fly off, no big deal.

I'll put together a video and post it on Youtube, so you can see what I mean. Gotta paint the barn and fence first though, so you'll have to hide and watch; sorry.


. . . . . Mac
Nothing difficult is ever easy!
Perhaps better stated in the words of Morgan Freeman,
"Where there is no struggle, there is no progress!"
Copeville, Texas
 
kitestrings
Regular Member

Joined: 23/04/2014
Location: United States
Posts: 99
Posted: 03:31am 30 Apr 2014
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Hi Mac, Madness,

I think the biggest problem with this approach is the one you stated up front; the losses. If you think about it, with the best of load matching and blade, drive, transmission efficiencies we're getting only a small fraction of the available energy converted to anything useful. In this scheme, you have the additional losses of converting the compressed air back to electrical energy.

You could, I suppose, just use the stored energy (in the form of compressed air) to drive pneumatic tools in your shop. I think in either case, the design of the turbine might well need to change to low-speed, high torque as a better match for the load. In some ways it is not unlike water-pumper applications (positive displacement)

I think your concept for braking is valid. In the late 70/early 80's Enertech turbines used hydraulic pumps for braking. They disconnected from the grid in real high winds and effectively pumped against a closed valve as a means of braking the rotor.

While it sounds simple, air is not without challenge particularly in cold climates. They've experimented quite a bit with pneumatic cars/fleet vehicles with only limited success (and range).

For the record, I'm old(er) too...

Regards, ~kitestrings
 
VK4AYQ
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Joined: 02/12/2009
Location: Australia
Posts: 2539
Posted: 03:49am 30 Apr 2014
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Hi Mac

I agree the storage of compressed air is one way of storing energy, however in large installations the size of the receiver is a cost concern and needs to be well constructed as a air event can be dangerous to workshop interior.

For the efficient use of air I think the motor needs a governor working the valves to allow reduction of air use with light loads, it is possible to modify the valve system of a small steam engine to do this.

At your size of equipment it is very workable and good fun. Many years ago I made a VAWT driving a compressor for heating and cooling Heat Pump, it worked but was cumbersome for the results.

All the best

Bob
Foolin Around
 
MacGyver

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Joined: 12/05/2009
Location: United States
Posts: 1329
Posted: 05:36am 30 Apr 2014
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kitestrings

"Losses" are inconsequential in my application. The wind blows for free and if I waste some, so be it. I set my blade pitch steep, so as to get more torque than speed. After all, the wind in Texas blows 24/7 so worrying about capturing a portion of it to run my toy engines is not a problem, for me at least.

Back in the day, I tried to size this application up by using a diaphragm pump, driven as an engine, using compressed air. I found I could get as much torque from a large-surface-area (bore) piston and a short throw (stroke) utilizing a mammoth flywheel and low air pressure (high volume!). I then geared things to create enough speed to operate a generator. I suppose it could be done on the megawatt scale, but I'm in it for fun, so I let it go at that.

The key to the hydraulic (pneumatic) breaking revolves around the capacity from the check valve at the pump head to the valve in the system; the closer they are together, the quicker the pressure head rises, thereby acting as a brake.

VKRAYQ
Hi, Bob; this season's maters are about 5" tall and ready to be hardened off and set outside. We had a LATE Spring this year. Maters are usually setting fruit by this time normally.


. . . . . MacEdited by MacGyver 2014-05-01
Nothing difficult is ever easy!
Perhaps better stated in the words of Morgan Freeman,
"Where there is no struggle, there is no progress!"
Copeville, Texas
 
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