Re-think that, methinks Shallow, lo head, freezing --- But yup, it'll work. Slight mod of a pelton wheel.
A low drop like that isn't going to produce much power. You are only looking at 18.9w for 3 feet of drop per 100 gallons per minute of water energy input. So we should probably round that down to 10w for a 3ft drop per 100gpm, after turbine and generator losses. That could be 600 to 700 gpm going through there. So they could be getting 50 to 70 watts there. Seems like a lot of investment for as little as 50 watts. But that's 50 watts 24 hours a day, 7 days a week. I would probably do it if I could. Then I don't know the inefficiencies of a set up like that. Most water power generation uses falling water or a turbine. I'm thinking this method of water drop is less than ideal. The only way to really know is to build it and measure it and see what you get and hop it's enough.
Lowell mills were powered by Francis turbines invented on site, about 15 foot head and 80 % efficiency in the 1860's and one built in 1890's still in operation in National Park there in a demonstration of the textile weaving. Have built small Banki or Mitchell turbines out of plastic, easy to build, easy to control, and will operate on a 10 foot or so head. Most of details can be made with torches, grinders, welding and hand bending. Several designs made by Peace Corps types and info on them. Biggest problem was varying frequency and voltage under load, using DC and batteries with inverter AC , like Honda with battery giving more stability, would seem to make a real useful system. While more expensive, the Francis turbine is still the most widely used and in a lot of smaller sites, except for cost of installation, can not be beat.
You would need an actual control system to keep 50 or 60Hz. Most common lowest speed generator types you will find 1800rpm to make 60Hz. These guys look like they are using closer to 3ft of drop.
Always wondered that if you are using solar, wind, or water and can generate a small amount and store in a battery, why not use a controller and charge batteries, everything DC, and then use inverters to make AC. There are some really good ones out there and the DC systems can use a dump heater if needed to get rid of excess charging current, and the batteries if they need more then the charging supply is putting out and don't have to worry about controllers, rpm stability or voltage droop. Saw old waterwheels in Georgia in the 1950's that were lighting 24 or 48 volt DC lights using generator and belts from a overshot waterwheel that had a lot of torque but I doubt was turning 20 RPM.
A real MPPT charge controller could take a wide variety of voltages from a permanent magnet alternator turning at various speeds and turn it into battery charging voltage
I've viewed a lot of turbines both in the water and out. when dealing with freezing temperatures its always going to be a problem but more importantly debris in the water is far greater and more difficult to deal with . The best systems by far draw water from far up stream to a settling pond then it is governed to turbines that have their own structure well away from the main stream .This way in the safety of the structure maintenance can be performed . a settling pond insures no debris or ice is going to create problems . Sand and grit are still going to wear away on the impeller and seals , so this cannot be ignored. the larger the settling pond less to wear out the impeller . What ever you install plan on pulling it regularly, NOTHING THAT MOVES UNDER WATER IS PERMINANT .
