Wednesday, September 2, 2020

Designing systems is an iterative process


Measured data. 8' diameter, six bladed wind-turbine. Very optimistically called "3.5kW system". Average about 70 Watts at 10 mph wind. Link one Link two

The column on the extreme right lists the number of hours per week you would need to run an 8' diameter windmill in a 10mph wind to generate the specified amount of irrigation water. Details of calculations included so readers can check them if they want to. Bust my chops if I made a mistake. I don't want to put bad information out there.

The devil is in the details. A 10 mph breeze is a respectable breeze and we usually don't get 50 hours in a typical summer week, at least not within a reasonable distance of the ground.

We might get significantly higher breezes when we have a storm system passing within 30 miles of our location. We get a lot of storms where we get wind but little rain.

My gut feel is that one, 8' diameter wind-turbine per 1000 square feet of garden/orchard would be a good starting point in my location.

One 8' turbine every 4000 square feet would provide enough supplemental water some weeks of the growing season but not all of them.


  1. You've already compared to solar energy watt-hours at your latitude/weather pattern? I would have thought a solar panel-powered downhole electrical pump would have fared better than a wind mill or wind turbine. The ranchers in Texas have pretty much gone solar now I think, and yes I know Texas is a little different.

    1. Solar trumps wind in Michigan except at high elevation close to Lake Michigan.

      But I don't know of any Michigan shops that can grow silicon crystals or amorphous silicon coatings and do the appropriate doping.

      On the other hand, there are many places with the wherewithal to crank out the guts of gear pumps.

      It is a mental exercise: What could folks bang out using local materials and skills. My mind is still partially in that fictional universe but playing these games helps keep my mind sharp.

    2. Now I understand. If you want that, then you might consider sticking with the old aeromotor windmill water pump which is a simple, oil-filled gearbox that lasts forever and a reciprocating downhole pump. They still make them and they can also be bought used, complete with tower.

      I've pulled these pumps before, and it's pretty easy. If your water table is that shallow, well then it will just be a few joints of sucker rod/pump tubing, and the pump will be at surface. The old ones used leather cups, but there are much better materials now.

      Here's a trick from oilfield sucker rod pumping (the hobby horse pump jacks): These systems are always counter-balanced - the prime mover crankshaft has a counter-balance to neutralize the sucker rod string weight to minimize required horsepower.

      Almost nobody does this, but a simple pulley, bucket, and rod clamp and some steel cable will let you counter-balance your water well sucker rod string so that the slightest breeze will get the windmill turning. Again, you're water is pretty shallow so this might not be as significant as a thousand-foot well.

    3. Also, as I'm sure you've figured out, if you are using a tank-fed gravity system for your water supply, in order to get 15 psi it will need an elevation of about 35 ft.

  2. It looks to me like you would be talking about a minimum of ten turbines per acre. Wouldn't water conservation methods such as mulch and drip irrigation systems be more efficient in the long run! I have to haul water as I'm off grid and wells close to me are 200+ feet. I use IRT mulch on crops I transplant over drip tube and drip lines next to other crops. It seems to work.

    1. Yes on water conservation measures. Drip irrigation systems are efficient .and. they still require water at approx 15 psi to open the diaphragms on the emitters.

      Just playing with words here, but suppose the US dollar puked like the Weimar Republic DM. Most people will not have an acre to work with. Most people will not be able to afford imported components. Most people will be under duress and have to maximize production on whatever growing area they have.

      In Michigan, irrigation is a no-brainer +50%-to- +100% yield. It might be of value to have a trail of bread crumbs in one way to make that happen.

    2. I'm using drop tape and dropping gravity from a trailer with 15 inch wheals! Currently I can load the 400 gal tank from the fire department well in about ten minutes with a 2" hose. Plan B is a has powered Honda pump from the nearby creek or a slightly further lake. I have two 12 x 24 hoop houses with three 3' beds each an run three lines of drop tape on each bed. I usually run three tanks of water a week in the hoop houses(they are plumbed to drop all at once. I water the green house tomatoes, peppers and cucumbers by hand from rain water catchment from the 12 x 24 green house. roof.


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