Nando,
Thank you for the swift and informative response. You are right, I do not yet know a great deal about the mechanics of hydroelectric power, but I am eager to learn from you and others. I am a second-year student studying Renewable Energy Engineering at the Oregon Institue of Technology. I have taken courses in fluid mechanics and elecrical power; but I know very little about small hydroelectric turbines.
Your statement about regulating the flow through the turbine with nozzles makes sense to me. I remember studying how larger Francis turbines have guide vanes in the scroll case that adust the amount of water flow. I was hoping for an easier way with very small turbines. If I understand correctly, in very small turbines you must shut down the system and physically replace nozzles to change the flow? You cannot adjust the flow while the system is running?
The results of my power calculations for 300 feet of 8-inch PVC Pipe and 26 feet of gross head are:
At 500gpm, the effective head is 24.5ft, the power output is 1224W (882kWh/month).
At 1000gpm, the effective head is 20.5ft, the power output is 2053W (1478kWh/moth).
At 1283gpm, the effective head is 17.3ft, the power output is 2223W (1600kWh/month).
These calculations take into account major pipe losses, but not minor losses. The addition of pipe fittings to the system will reduce the power output from the numbers shown. I am assuming a combined efficiency of 50% for the turbine and generator. I did not do calculations above 1283gpm because 1283gpm is the optimum flow rate for an 8-inch pipe, above which additional flow does not result in increased power output. I also did calculations using other pipe sizes (6-inch and 10-inch). I am willing to use the size that makes the most economic sense.
I am planning a grid-tied system because here in Oregon we can sell back to the utilities as much power as we use during the year.
I have only started to investigate turbines. From what I have read, Banki crossflow turbines are ideal for low-head, high volume applications, but I have not been able to find a single manufacturer of small Banki turbines in the United States. Would I have to build one from scratch?
The idea of using an induction motor for a generator is very interesting to me. I would very much like to learn how to do this.
Thank you, Nando, for taking the time to answer my post and share your knowledge. I am eager to learn from you.