Amish wind problems

I've been talking wind with an Amish wind turbine engineer. That's been sort of unexpected, and fun, for me, not just because of my own Quaker background, but because Amish are such communal and pleasant people, and because of the engineering problems involved.

Our Amish engineer, whose privacy I'll protect by not naming him or putting up photos, is developing a shop to produce wind turbines. The Amish generally don't have electricity in their houses, so these turbines are designed to produce compressed air. They use air for machine tools of all kinds in manufacturing. A lot of Amish farms are actually small manufacturing facilities, turning out anything from wooden park benches and cabinetry to, well, wind turbines. This particular plant will make small-to-medium turbines for farm-scale installation, each turbine connected by an air hose to a large compressor tank. By both saving lots of air in storage tanks, and by scheduling manufacturing and other shop work for breezy days, the Amish can have compressed air without doing what they normally do, which is run a small gas engine to run the compressor. Gas has been expensive lately, and not all Amish church meetings allow the use of gas engines, so there's reason to think that wind compressors will be welcome additions to the Amish toolkit.

The last Amish family I got to know, several years ago in western Pennsylvania, used air in a very tidy and well-developed shop to make harness and tack out of leather. The shop, with homemade bridles, saddles and harness hanging everywhere, was a magnet for every horsey person in a hundred mile radius, and business seemed very brisk.

(I once went hunting on Peter Brown's farm with the four sons of this family. Because it was far, they couldn't drive buggies over to the farm, so I picked them up in my vehicle, a 1975 VW bus, which I sill have. At five am on a back road in Pennsylvania, with four Amishmen and a hairy Englishman in a VW bus, all pacifists armed to the teeth, I wondered what might have happened if I'd been stopped for speeding.)

There are some interesting problems to solve with a wind compressor.

The first is the cut-in speed of the compressor. A normal wind generator has a certain mechanical inertia to be overcome before it will run. The level of inertia is related to the strength of the magnets used, or electromagnets, and the quality of bearings. In a wind compressor, there's a piston to crank, and the inertia level is related to the compression ratio of the piston and cylinder and their mechanical efficiency and lubrication.

This could lead to high inertia. If you don't change your compressor crank oil, if it's cold out, and if you have a high compression ratio, your turbine might not run at all until you get a fairly high wind. In any case, you'd be better off with a turbine blade design with an aerodynamic shape that can produce high torque at low speed, to overcome the inertia and get the compressor cranking. Manufacturers of off-the-shelf wind turbine blades don't make these kinds of blades. So our engineer needs to find a way to make, or have made, a different kind of blade, with a wider base and higher pitch at the base, than a normal skinny, high pitch, high-speed small generator blade.

Another problem will be telling customers fairly what the capability of the compressor is. With an normal gas compressor, the manufacturer's label will tell you what to expect, and unless there's something wrong, that will be what you get. In the case of a wind compressor, the amount of air you compress will depend as much on how windy a site you have, and how high your turbine tower is, as on the actual label efficiency of the compressor. The Amish are required by their religion to be fair in business practice and to give fair value. So our engineer needs to be able to relate wind speed to the power output of the prototype wind compressor, producing in effect a power curve for the generator to give to customers and potential customers, except in this case power produced will be measured in compressed air, not in KWH. So he needs to measure the wind on a prototype generator tower. I've provided some analog equipment to do this job, but a computer-logged system would be much better. We have several, but the Amish aren't allowed to use them.

Interestingly, the power curve will not be sigmoid or logistic as is usually the case with a wind generator. It will exhibit an exponential curve to begin, followed by a declining slope, because any piston-driven compressor loses efficiency/stroke as stroke speed increases (because of valve and air intake capacity limitations).

Finally, users of these wind compressors will need to pay close attention to air efficiency and storage efficiency. Most compressed air users tolerate a lot of leakage. The compressor needs to run to keep the pressure up, and you have to exercise the compressor at least daily, and bleed out water that accumulates in storage tanks, so a little air leakage is generally not such a bad thing, and a downright convenience when from the little valve at the bottom of the tank where the water accumulates. In the case of a wind compressor, unless you are willing only to work when it's windy, or have a site where it's always windy, you had better have good storage and little leakage. The customers will need an instruction manual that emphasizes efficiency and leak control.

These problems are all kinds of engineering fun, and, as my wife noticed yesterday, much more fun than teaching classes, so I've been Hanging out With the Amish.

Luckily we have students at Unity College in our Sustainability Design and Technology major who want and need to learn this kind of practical problem-solving engineering, so we can involve a couple of students in this exchange. Not a whole class, though. That wouldn't be fair.

As an added bonus, students will get an education in cultural diversity and sensitivity and be able to observe first-hand the case-study in practical ethics that the Amish just naturally are, which is not such a bad additional set of outcomes.

The compressor power curve problem is very good math, and statistics, for students to have to learn and apply too.