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.

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.
http://www.scoraigwind.com/
http://www.otherpower.com/
There are many links from each of these sites for more than you wanted to know about the subject.

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.

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.

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.

http://www.wired.com/wiredscience/2010/03/backpack-hydroelectric-plant/

interesting...

Micro-micro hydro power... http://www.re-energy.ca/pdf/hydroelectric-generator.pdf

:P

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: http://www.microhydropower.com/ 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: http://www.ekatinc.org/