The Walden Effect: Farming, simple living, permaculture, and invention.

Microhydro assessment: Measuring flow

Despite wanting to consider energy efficiency first, I was still curious whether the copious water on our farm would be a good fit for microhydro power.  The first step in assessing a site for microhydro is to measure stream flow.  Scott Davis suggests two easy methods.

The weir method is used in large streams or rivers.  The water flows through a notched weir that forms a waterfall.  You can use various tables or formulas to determine the flow rate of your creek based on the width and depth of the water in the weir's notch.  I didn't feel like constructing a weir, so I moved on to option 2.

The container method consists of finding a spot where all of the creek's water runs through a culvert or pipe, then sticking a five gallon bucket underneath.  Time how long it takes for your bucket to fill up, then use the following formula to determine your stream's flow:

Flow (gpm) = Container size (gal) ÷ Container fill time (sec) X 60

As you can see in the embedded video, I found a spot where a huge root mass had channeled all of our smaller creek's water into a waterfall, so decided to try out the container method of estimating stream flow.  I couldn't fit a five gallon bucket under the waterfall, but a one gallon cook pot slipped right in between the roots and filled up in 3 seconds.  Our flow in that creek is approximately:

Flow (gpm) = 1 gal ÷ 3 sec X 60 sec/min = 20 gpm

Our smallest creek's flow is pretty low, but is definitely within the realm of microhydro power.  In fact, Scott Davis notes that you can get power from streams running as slowly as 2 gpm (gallons per minute.)

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This post is part of our Microhydro lunchtime series.  Read all of the entries:

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About us: Anna Hess and Mark Hamilton spent over a decade living self-sufficiently in the mountains of Virginia before moving north to start over from scratch in the foothills of Ohio. They've experimented with permaculture, no-till gardening, trailersteading, home-based microbusinesses and much more, writing about their adventures in both blogs and books.

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It's a vertical shaft axial flow propellor turbine.

From microhydropower, the LH 1000. Look at the power output chart on the bottom of the page.

Comment by Roland_Smith Wed Mar 3 15:58:12 2010

There are many variations of things to generate electricity using a stream. Many of these can be completely home-made. Look at pelton wheels and even squirrel cage fans from vent systems or from the old water coolers I remember as a kid. These can drive various permanent magnet alternators that you can build or buy.
Here are a couple of sites for lots of information including wind, solar and water.
There are many links from each of these sites for more than you wanted to know about the subject.

Comment by vester Wed Mar 3 16:35:21 2010

Wow, I wander away for a while, and the comments go crazy. I'm thrilled. :-)

The Microhydro book mentioned the LH1000 as one of its top choices for this sort of situation too. But what Roland emailed me about its efficiencies being only 41% to 53% compared to 90% for a big system is distressing. I guess that may just be what we have to put up with when dealing with a small system?

I'm intrigued by the DIY options too --- Mark has mentioned a few in the past, which might actually include one of the ones Vester mentioned. The Microhydro author was down on DIY systems because he thinks that the much lower efficiency from them means you have to scale up all of the components you do have to buy and often don't come out saving any money. I'd love to hear from someone who's actually tried it and looked at the efficiency and the resulting price difference between DIY and store bought per unit power.

Comment by anna Wed Mar 3 18:24:55 2010

In general, small energy conversion systems will be less efficient than big ones. This is an unfortunate fact of life, grounded in the laws of physics and a bit of economics too.

Look e.g. at the LH1000. If you were to make the propeller diameter twice as big it would be able to pass four times as much water because the throat area scales with the diameter squared. Losses in things like bearings and the generator usually do not scale with the square of size, but much less. So a larger system will be more efficient in general. (I'll try and expand on that in the series. First installement almost ready...)

And while I do not want to bash DIY-ers, power conversion systems like engines and turbines do take a lot of effort to optimize. So unless the DIY-er in question is experienced and well-versed in both theory and practice of the matter at hand and has access to a well-equipped machine shop, I wouldn't bet against a store-bough unit (if the market is mature). For starters, most DIY-ers will probably not be able to build their own generator, and if you are on a tight bufget you'll probably end up using an alternator from a car or possibly some electric motor. That will almost certainly not be as efficient as a generator built for the task.

Comment by Roland_Smith Thu Mar 4 02:13:59 2010
Is there any alternative energy system where you don't lose massive amounts of efficiency with a small, DIY version? Maybe pedal power?
Comment by anna Thu Mar 4 06:42:54 2010

There are some things that you can do to improve efficiency, but most of them will be out of reach for DIY purposes, I think.

Concentrating on water turbines for the moment, the most obvious losses in my opinion there are

1) friction losses in the bearings (and seals, if any)
2) flow losses due to turbulence
3) efficiency of the generator

Point 1 is something you you can't really do much about. You could try Hydrostatic bearings (think air hockey table) since they have low friction, but for a small installation the energy required by the necessary pump will probably eliminate any gains.

To solve 2, you really need to have a background in engineering/physics and do a lot of experimeting. Some CFD might come in handy as well. Any energy conversion machine wil have a set of circumstances under which it works best. Basically you need to tailor your turbine to your conditions for it to work best. For example for a propellor type turbine like the LH1000 the gap between the rotor and the tube needs to be as narrow as possible to prevent losses.

The same goes for 3. Ideally, your generator should be constructed to perform best under the circumstances that prevail in your case. Small water turbines generally do nut run fast, so you need an alternator with a lot of magnetic poles or gears to pick up the speed which are expensive and hurt efficiency. You'd want an alternator with permanent magnets in the rotor, so you don't lose power by having an electromagent in the rotor. Car alternators aren't really suitable because of that and because thay are designed to run at high speed (several thousand rpm). Small alternators generally are 50-60% efficient because they are restricted in size and weight for use in cars and bikes. By contrast the huge alternators in powerstations do not suffer from such restrictions and can be up to 98% efficient.

As for pedal power, a well-maintained bicycle chain and derailer can give you 90% efficiency. Of course, if your tires aren't properly inflated you'll spend a lot of energy there flexing the rubber. :-)

Comment by Roland_Smith Thu Mar 4 16:15:25 2010
You make pedal-power sound very enticing! That's Mark's first choice for alternative energy at the moment, mostly because it seems to be very DIY compatible.
Comment by anna Thu Mar 4 16:51:00 2010
You know I can't think about pedal energy without thinking about soylent green. :)
Comment by Rebecca Thu Mar 4 17:11:16 2010
That's odd --- I don't remember that part of the movie...
Comment by anna Thu Mar 4 19:28:38 2010
near the beginning, when they are in their apartment the old guy has to pedal to light up the single bulb in the ceiling. I think. its been what 8-9 years since arcadia had swil show it?
Comment by rebecca Thu Mar 4 22:17:28 2010


Comment by Shannon Fri Mar 5 04:29:07 2010
You all are right --- that backpack version is extremely cheap per watt compared to the units mentioned in the hydropower book. I can't quite seem to tell what's included in it, though. Is that just the turbine (in which case it's not such a good deal) or a whole system?
Comment by anna Fri Mar 5 07:35:16 2010
Rebecca --- now I remember!
Comment by anna Fri Mar 5 12:21:10 2010

Micro-micro hydro power...


Comment by Shannon Tue Mar 9 02:06:03 2010
I love it! Who knew something made out of plastic spoons could be so elegant. :-)
Comment by anna Tue Mar 9 06:30:26 2010

Hydropower is hard to beat for reliability if you've got the water. Head is more valuable than flow. Makes a great supplement to solar in Kentucky where the winters are generally cloudy and wet. Don't sweat the inefficiencies of the small systems. It's the reality. But they're not cheap. Best equipment is from Energy Systems and Design: I've installed a couple of their older "stream engines" (before the permanent magnet generators) and will be upgrading mine and adding another. I'm at:

Comment by solarbobky Thu Mar 17 18:51:38 2011
You can follow the links above to see where we also assessed our head and estimated how much power we'd get out of the system. Unfortunately, our low head systems probably aren't going to happen, but I can see how microhydro would be a great choice for people with less flat creeks.
Comment by anna Thu Mar 17 20:26:03 2011

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