I've recently been in contact with PowerPal in Canada, and they were very helpful. I've recommended one of their turbines to a consulting client in Canada.
These are not high tech turbines, and they require regular maintenance on the submerged bearings (even the latest version). Every 12 weeks I believe!
If you want a low-head unit that will last a long time with little maintenance, go with the ES&D:
http://www.microhydropower.com/Low%20Head.htm
However, it is much more expensive and is 3-phase rectified to DC only (thought there are 120v and 220v versions for long transmission lines). For differing heads, you can get different length draft tubes, so the ES&D can work from 2 to 10 feet of head.
The PowerPal is AC output only, with voltage and frequency regulated by the control unit located away from the turbine. It is NOT adjustable for head, 1.5 meter is your only option; the intake sluice and turbine runner are designed so that close to the correct RPM will always be happening, and the regulator just tweaks it. However, there is info on their discussion forum about replacing the turbine runner with a homebrew version, to give proper RPM at higher heads (after extending the draft tube of course).
The PowerPal is also sensitive to reactive loads, like large battery chargers (ouch). These can cause the stator to overheat and burn out. Compact Flourescents work fine on it -- but you should source good CFs, not the crappy Chinese ones that have a high power factor (very reactive). You could add capacitors....but probably would need to do that to each CF, as total load reactance would vary depending on how many were turned on. It's no longer difficult to find low-power-factor CFs.
However -- if you need an energy source that doesn't have any storage, the price is right on these PowerPal turbines. Under $1000 for the entire system, including intake sluice, turbine and regulator, and shipping to the US or Canada from Vietnam.
That's 1/3 the price of the ES&D unit, with no need (or option) for a battery bank and inverter. Just be aware the PowerPal is maintenance-intensive.
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