Hydro Power - direct drive v. electrical

[Michael Daly]

Too far south for my tastes. :-)

Mike

[Lawrence Wasserman]

Not exactly modern, but try a search on "Ben's Mill" There's a chapter on this guy in "The Workshop Book" I think the author is Steve Landis. It's really amazing what this guy does with his shop. I think the book is 15 or so years old by now, not sure the mill owner is still alive.

[Norman D. Crow]

I'm pretty sure he's gone by now. He was about 2 days older'n dirt when I met him in '86!

[Jay Pique]

I was hand priming a bunch of cabinet doors today and got to thinking about this again... Given the magnificent advances in hydrodynamics and materials technolgy, my guess would be that we could increase the horsepower of the wheel by at least twofold by rebuilding the wheel. I plan to retain the aesthetic to the extent possible, but I won't sacrifice performance. If the wheel's got to go, it goes. Provided I can get approval.

The next question I have of myself is what are the efficiency losses in converting from hydro to electric? Are these more or less than the efficiency losses in gearing X number of machines to a very modern belt system? Is the equation always going to come out on the side of electricity or do other factors come into play - such as the maximum load you could expect at any one time.

It might be "worth" it to go all electric if you can sell back into the grid, but is it the proper use for a historic building? How about a split system - ie. drive a mill and a large bandsaw with part of the power, and convert the remainder to electricity...

JP

***************** It's Electric!

[Robert Bonomi]

classical 'open wheel' designs have a quite low efficiency rating.

The 'theoretical' power available can be computed, given the 'head' and the flow rate. Its roughly 100GPM at a 4.4' head, per horsepower.

A 'bucket brigade' type wheel, with _no_ spillage, captures nearly 100% of that potential energy. The biggest loss component is the mechanism for ensuring the buckets traverse the 'up' side _empty_.

Well, under _optimum_ operating conditions, a 'small' (in this context meaning 2-10 hp) electric motor is about 85% efficient. under that range, and the efficiency goes _down_. Dramatically downwards, as the the power-rating gets smaller.

*BIG* hydro plants can capture significantly over 90% of the energy of the water passing through them.

Again, efficiency decreases with deceasing size, but you should be able to approximate the efficiency of a like-sized motor -- the generator is nothing more than a motor 'running backwards'.

Assume 80% efficiency for both the generator and the motors it drives.

You only get 64% of the generator input "water power" at the motor drive-shaft. (note, the 'generator input' is the same as the 'shaft output from the water- wheel. any inefficiencies in the water-wheel itself affect both systems to precisely the same degree.)

A good mechanical-transfer system will have efficiency ratings in the high 90s. This almost always runs rings around a generator/motor set-up.

*HOWEVER* there are a whole bunch of -other- considerations: Do you require controlled 'variable speed' setting capability? Can you _tolerate_ randomly-variable operating speeds? Without very exotic controls, water-wheel power output is tied to shaft RPMs. to transfer more power, you have to spin the water wheel _faster_. (or operate to allow spillage, with the resultant energy-losses -- a.k.a. reduced efficiency -- at less less than full capacity) What about 'overload safeties'? Can the power 'producer' and the 'consumer' equipment be located close enough together? Do the equipment users have the requisite skill-set for 'turning on' an additional piece of equipment -- you don't just push a button or flip a lever; like driving a car with a manual transmission, you have to know how to manipulate a clutch. Stalling the "engine" is a *really* bad thing to do.

That kind of 'conversion' gets piss-poor efficiency. You -cannot- generate the proper A.C. directly -- you don't have the controls to ensure the proper shaft RPM from the water-drive. Nor the stability of it So, you'll have to either generate DC, or generate 'random frequency/phase' AC which is rectified to DC, and use -that- to *carefully* generate the proper in-phase power to feed back into the grid. Sub 50% efficiencies are -not- at all uncommon.

>