A while back, I posted about windmills and thermal power. I have an idea on thermal/wind and want your opinions. If you build a greenhouse around the base of an existing windmill tower, then sheath the tower with black material so that the tower would be like a "smokestack" up from the greenhouse. Could the greenhouse and "chimney" produce enough thermal draft to drive the windmill blades during the heat of summer when winds are still? I played with a toy pinwheel over a stove eye and noticed the heat spun the wheel some. An added feature of this thought would be that in winter when winds could drive the windmill, the green house could be used conventially instead of as a "power tank". Lets bounce this around.

-- Jay Blair in N. AL (jayblair678@yahoo.com), December 17, 2000

Answers

A very interesting theory. There is a Christmas decoration that has a windmill-like blade that uses the heat rising from a candle for propulsion.

You would have to use a special mill blade in that a conventional windmill is designed to use the wind coming from the side of it. With your design it would need to trap the upflow from the bottom. I really doubt that you could get enough upflow to power a mill that is doing work, but that's strictly opinion.

Keep us posted on any experiments.

-- Notforprint (Not@thekeyboard.com), December 17, 2000.

If it works, you will be famous. There is a small problem to be overcome in that the Venturi Effect normally would not be enough to do any useful work on the windmill blades that operate under the Bernoulli Principle. Your task is to prove one, or perhaps both, of these concepts wrong. Good luck.

-- JLS in NW AZ (stalkingbull007@AOL.com), December 17, 2000.

Notforprint, I would think the only mod required would be the addition of fin extenders to ride as much of the thermal wave as possible without adding too much weight. True winds are generally horizontal, however, a circular blade can be motivated from either axis.

-- Jay Blair in N. AL (jayblair678@yahoo.com), December 17, 2000.

i dont know enything about windmills. what im wondering if a windmill can be kicked out of gear like not pumping water but the wheel still turning. if so why cant a chev. alt. be driven to charge batts. when its not pumping water? eny coments? i live about 50 miles from Harry Rose when the weather breaks im going to go talk to him. happy holidays. Bob in se ks.

-- bobco (bobco@hit.net), December 17, 2000.

Wouldn't there also be a problem with the wind blowing over the tower with the resistance from the covering? You could put a woodstove to boost the heat upflow ie the tower as the chimney.

-- Tom (Calfarm@msn.com), December 17, 2000.

What a great idea! Could you use the pinwheel and a mini greenhouse to prove the effect would be great enough? For example, take a pinwheel off the stick and reposition it so that it hovers over a mason jar "greenhouse" complete with a mini tower built from scrap wood sheathed in black plastic. I have played with the candles and spinning angels from the heat myself and the idea obviously works, but the blades were horizontal...perhaps for your concept, one would need a windmill that could be repositioned from horizontal in the Summer to vertical in the Winter? God bless.

-- Lesley (martchas@gateway.net), December 17, 2000.

Lesley, Great idea on the model. The automotive and aerospace industries use model shops to build scale test units all the time. Tom, The wind resistance is a biggee, might be avoided if the shrouding had curved surface to reduce wind resistance of the structure.

Bob, The alternator should work. A fella I work with said he made a windmill with one using 12 v system and mounted the blades directly to the alternator. Produced enough to keep the battery up to drive a light and 12 volt tv at his fishing hideaway cabin.

-- Jay Blair in N. AL (jayblair678@yahoo.com), December 18, 2000.

What if, during the summer when you are using the chimney for draft, you arrange some sort of enclosure around the blade part, with an opening above the blades. I'm not much of an engineer, but I think that with that arrangement, and possibly a smallish top opening, say the size of the chimney below the blades, any passing breeze would tend to suck air out of the chimney, increasing the draft, no matter what direction it was blowing at the time. Isn't that how Venturi works?

-- Laura Jensen (lauraj@seedlaw.com), December 18, 2000.

Actually something like that has been done---in Spain or Italy I think. They used a 13 acre area, roughly circular, covered it in plastic with the edges open for air flow. The plastic gradually sloped upward toward the middle where it directed the air flow to this 600'(?) black tower. The tower was something like 12' in diameter. There were two wind generators, with a vertical axis, one at the bottom and one at the top of the tower. Seem to me it would produce something like 55mph winds. It produced alot of electricity as I recall. I read about it in Popular Science years ago so some of the dimensions are a little fuzzy. I thot it was a really cool idea. I've wondered if a much smaller version would work in a solar chimney used for ventilation.

-- john leake (natlivent@pcpros.net), December 18, 2000.

John, I spoke to the tinkerer at work and he said the same that he thought it was in Spain. Something else he suggested was making a cylinder shaped squirrel cage blade about 20 ft across and making a mill that could capture the wind and also be driven by the thermals at the same time.

-- Jay Blair in N. AL (jayblair678@yahoo.com), December 19, 2000.

The real problem is generating the electricity once you harness the wind. Any type of coil that is bought off the shelf is going to be expensive, and Chevy alternators need a certain amount just to get started. I understand that you have to rewire the alternator just to get it to work. Is that right?

-- Dan Thomas (mrdanthomas@hotmail.com), February 01, 2001.

Why not use a small electric motor THAT GETS ITS POWER FROM the windmill. The windmill provides small amount of juice to power the small motor....which, in turn, turns the windmill. It's self perpetuating. OR..solar panel to power the small motor, which turns the windmill...which provides big power. Hydro power is completely, and eternally...eliminated.

-- Bob Murray (susanmuray@hotmail.com), February 11, 2001.