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Roof-top Wind Farms

- The Symphonic Sounds of a Lifestyle

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by Chris Devaney

35-45 MPH

Forget about sleep!  It’s not going to happen.  This wind regime doesn’t occur very often, but when it does...

The Air-X’s continue to spin wildly; howling and occasionally screaming at the wind.  Up and down they accelerate; both are in a constant frenzy.  One will spin out of the wind, decelerate rapidly then charge right back into the wind for more.  This is excitement!  But things deteriorate rapidly.

A quick flutter on the west side, east side holds into the wind then spins out.  Peace rushes in but only for 30 seconds and then the fury resumes.  At the upper end, they seem to spend too much effort in fighting the wind, and it appears that they are losing the game and being battered unnecessarily.  Out of mercy, I’ll throw the stop switch - they’ll fight the wind again some other time.  For the Air-X, the battle is over, the wind has won.  Faithful, hard-working, robust, it is all that I could ask for in a small wind generator.

The Mallard, still a magnitude quieter than the Air-X’s, has plenty of fight left.  I can see and hear the tail-vane occasionally shudder as a gust of wind tries to take it from the side and knock it out of the wind.  The gust fails and only serves to spin the rotor faster.  All six blades are moving so fast I can’t see them anymore.  Striking back at the wind like Hell hits the sinful, the Mallard searches for, and hunts down the wind.  The sound is like 1000 . . . no, 2000 Tibetan monks simultaneously chanting “OMMMMM” into a microphone with no pause for breathe, just a long continuous chant until the wind gives in.  Oh, what a glorious battle!  This!  This is how electricity should be made!

Output: With the Air-X’s shut down, power output is left up to the Mallard, the fighting monk.  Output is around 20-30 amps with uncontrolled voltage that may temporarily exceed 17 volts.  While the batteries will accept the high voltage especially if they are in need of charging, the AC inverter that converts battery DC voltage to 115 VAC complains.  Above 17 volts the inverter shuts down the AC side of my electrical system and I have a momentary brownout for having too much power!

45-50+ MPH

Stand back!  This could be the end of us all!  The Air-X’s are out of the picture now.  Like Davy Crockett left standing alone at the Alamo, the big green Mallard is on its own to defend the roof against a menacing 50 mph wind.  It could be that it is at the peak of its endurance, but then again, maybe not.  “Bring it on, you dirty sons -of-Satan!” the Mallard taunts the wind.  A strong gust suddenly attacks off to the right in an attempt to spin the machine out of the wind and kill it.  The big, green, sheet-metal vane shudders slightly and the Mallard quickly flicks its head to capture the gust, accelerate, and almost immediately face back to the prevailing west wind for more.  Thump, thump, thump.  The mast starts vibrating above the top mount making contact with the trim across the lean-to roof.  Uh-oh! Could this be the weak link, the Achilles heel that brings the big green Mallard, the king of the wild frontier, to its knees? 

Another slight ripple across the tail-vane, but this time the Mallard stays facing the wind, blades spinning furiously and roaring back at the howling wind.  By God, I think, he’s actually enjoying the battle!  Another side thrust from a gust is handled.  Its energy captured but followed by some turbulence that causes the tail-vane to oscillate left and right a couple of inches each way and a brief struggle to maintain stability ensues.  But the long pitch from the center mount to the tail mount results in less than a half inch variation in the rotor direction so the Mallard has no trouble in regaining its footing.  No flutter, no hunting for the wind, just head-on, rock-solid stability.  No, I’m convinced there’s more fight left in the big green Mallard.

The energy in the wind scales with the cube of the wind speed. There’s almost twice as much energy blasting through the Mallard at 55 as there was at 45 mph.  But I don’t think Ace Bass cares; he’s in the fray until God calls him home... or the 50 amp fuse blows and it may be close to 50 amps now, I don’t know, but the wires are warm.  This is my kind of wind machine!

Years ago I lost hateful Hilda because I was a fool and didn’t act. I’m wiser now, age does that sometimes.  So I throw closed the stop switch.  I guess I’ll never know the Mallard’s limits.  But I’ll sleep tonight and dream about it.

Here’s some links for further information.

Southwest Windpower (Air-X) : www.windenergy.com

Mike’s Windmill Shop (Mallard): www.mikeswindmillshop.com

AWEA (American Wind Energy Assoc.): www.awea.org

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