Making the most from brook in back yard: waterwheel generator?

February 25, 2006 8:57 PM

On our property there's a rather substantial brook running through it, which runs year round and doesn't freeze over. It's probably too wide for a traditional undershot waterwheel (at least 12 feet across at its most narrow), to supply some alternate power to our house, but maybe there's something else that could make the most of the constant flowing water?
posted by Gudlyf to science & nature (16 comments total)

Belt-driven ceiling fans, instead of air conditioning?
posted by frogan at 9:08 PM on February 25, 2006

How much drop is there on your property, and how much can you manipulate the brook? If there's a drop you might consider "micro hydro".
posted by anadem at 9:14 PM on February 25, 2006

Like anadem, I too suggest you consider a micro hydro system. They essentially consist of a long pipe, a submerged turbine, and a small generator. You'll want to estimate the head (or drop) and flow of your stream to see if it is appropriate for a micro hydro system.
posted by RichardP at 9:26 PM on February 25, 2006

Like everyone else is saying, you do need to figure out how far the water can fall because that (and flow rate) will determine the amount of potential energy it has. Remember E=mgh (m=mass in kg, g=9.81m.s^-2, h=height in metres) so P=fgh where f is the flow rate through your hydro device in kilograms (equals litres, since it's water) per second. That gives you watts available in the water.

You then need to think about the efficiency of the conversion (micro hydro, waterwheel, whatever) system you're going to use. Micro hydro systems (long pipe with turbine at the end) work well with long falls (ie high pressure, high velocity, not so high flowrate). If you have very little fall available, they will probably turn out to be quite inefficient.

If you've got maybe 2m of fall, a traditional bucket-waterwheel is possibly more appropriate: make the diameter match the fall and you'll get an effective fall (in terms of energy recovered from the water) of about half the diameter. That's only good with huge flowrates and a small fall. Any more fall than the diameter is wasted, big buckets (lots of water) are required to get sufficient torque & power.

As for 12' wide, that can be changed with a couple of days and a shovel. Damn it up above the waterwheel (assuming you have even 2m of useful fall) to a couple of feet wide.

If you're going the undershot route, you can still narrow the stream with clay earthworks where the wheel is. Just make it a bit deeper there too. Keep in mind if you halve the area through which it flows, the velocity will double. Increased velocity means you can extract power more easily using an undershot wheel, ie a smaller one. The walls of the narrows will need to be impervious to erosion, obviously.
posted by polyglot at 1:44 AM on February 26, 2006

oops. s/Damn/Dam/; let us not have accursed earthworks.
posted by polyglot at 1:44 AM on February 26, 2006

If you have enough flow, and need (admittedly a fairly small amount of) water pumped uphill, the hydraulic ram pump is your friend. They (well, some of them) also have the very pleasing attribute of being started by hitting them with a hammer.

They'll run for years without maintenance. A friend of mine had been in her house 15 years, and had never known where their water was coming from. Once summer, she found a little box near a stream on her property. In it was a little ram pump, that had been clicking away since the previous owner moved out.
posted by scruss at 5:24 AM on February 26, 2006

Modern reaction turbines can be designed to operate on as little as 2' of head. There are also propeller style generators that work well if you have strong flow and can't (most places require a permit to dam surface water) or don't want to run pipe and setup a dam.

It is rarely cost effective to setup off grid power unless your area supports net metering. However if you have a substantial heating load you can setup up a simple system to provide heat. Just hook your alternator directly to one or more electric heaters. Electric elements are essentially immune to low voltage and frequency variations so you don't have to worry about conditioning the power. Because you have a certain steady state heat loss in all homes if you don't go over board on the generation you can just let the heaters run 24/7.

In the summer you can divert the heating capability into electric hot water. Best to run a preheat tank in series with your regular tank and add scauld protection via a mixing valve. Or heat a hot tub, pool or sauna.

If your feeling a bit more ambitious I've always wanted to raise tilapia. They love the arerated output of a turbine, you can use the turbine to heat the water to extend your growing season if that is a problem, and they are essentially fool proof.
posted by Mitheral at 7:06 AM on February 26, 2006

Best possible use: 1) Lawn chair, 2) cold beer, and 3) mellow out...
posted by jsteward at 9:36 AM on February 26, 2006

Home Power Magazine is a good resource for this sort of thing; they specialize in the do-it-yourself small scalle RE projects, such as micro hydro. They have 'how I did it' articles on the subject, test data for various equipment, legal/electrical code issues, as well as pointers to various workshops on the subject. Worth a look if you can find it in your local bookstore/library, and they also have searchable archives/purchasable PDF's of back issues.
posted by bemis at 10:23 AM on February 26, 2006

Damn it up above the waterwheel (assuming you have even 2m of useful fall) to a couple of feet wide.

Before you do something like this you might want to check on local laws/etc with respect to the town/county's rights to running water. My parents have a creek that is technically on (or at least immediately adjacent to) their property, but can't do anything with it because of such laws. Their neighbor had to petition the town to even put a garden within 20 ft. This all started when the creek (supposedly) needed to be dredged because of flooding somewhere, so even if you do make modifications, you may find that a few years later the town comes along and destroys everything. (they even cut down what was basically forest for the entire area within 20ft of the creek). Also, damming it might have an effect upstream.
posted by advil at 11:13 AM on February 26, 2006

My sister's house is off the power grid, and she uses expensive and complicated solar panels. She added a small water wheel generator that I believe is a modified bicycle wheel.

Her water flow is two miner's inches (the amount of water that will pass through two one inch holes one foot below the water surface) and that power exceeds the solar.
posted by StickyCarpet at 11:17 AM on February 26, 2006

Ken and Polly Haggard have done this for years.
posted by hortense at 1:55 PM on February 26, 2006

Bribe some beaver to move in and build you a mill-pond dam. That sets up a major conflict between animal rights and any water-rights regulations. Just make sure the beaver know when to stop, or you may be building your mill wheel in the basement.
posted by Kirth Gerson at 2:49 PM on February 26, 2006

you really want to go with micro hydro, as suggested you can make it with very small head, and you will not need to fuck with the stream too much, preserving the nice flow and making any animals that live in the stream happy. with an all year hydro source you will make more energy than solar or wind by far simply because it flows 24/7 combined with energy efficient lighting (cfl's) proper insulation and energy star appliances you could probably go 100% renewable. good luck.
posted by stilgar at 4:41 PM on February 26, 2006

John Hermans, the most productive individual I've ever met, lives a few kilometres from me in a passive/active solar house he built himself, with power and water from his own micro-hydro installation in the Nicholson River (which would probably qualify as a decent sized brook in any country with real rainfall). He had to build a weir across the river to make it work, and his design includes a fish ladder to mitigate the environmental effects of the weir.

Here is an absolutely beautiful water pump he built for a friend who lives on the Brodribb River. It's powered by an undershot waterwheel (in fact, it mostly is an undershot waterwheel) and needs no head, just flow.
posted by flabdablet at 6:01 AM on February 27, 2006

Second Home Power magazine. I've been drooling at their micro hydro coverage over the past 2 years. They are like the old Boardwatch magazine - articles by people who do it, for people who want to do it.
posted by QIbHom at 2:18 PM on February 28, 2006