AHhh OK. I am going to build a crossflow turbine, trying my best to copy the designs of the Ossberger. It actually uses the water 3 times to create the best efficiency. Google Ossberger turbines and read the info and study the design. It's not all that difficult to build, IF one pays enough attention. A Harris Pelton will cost me nearly $2000.00 to get shipped down here. I am going to build an axial flux alternator from this forum, to drive directly from the turbine. I would love to try ceramic bearings, but, they are costly. I have a bunch of used motor wire in excellent condition, and am using used sawblades, thicker than skil saw or table saw blades, for the turbine sides. I will measure the thickness for you, if you want me to.
The crossflow, designed correctly, the water will strike the blades 2 times, then exit the turbine under a vacuum, pulling the water into the turbine a little better or stronger, according to other info I have read. This vacuum is referred to as "Torque tubes". My 20 GPM will be minimal amount, as in, right now and for the next 3 months. We get night time showers, occasionally, during our "dry season".
I will pipe 4" PVC down to the turbine, from the dam. The turbine is designed with a weighted "Flapper" type water diverter, that rides right over the spinning blades, to make every bit of water that enters the turbine, strike the blades, thus, minimal splashing to speak of. There is also a second "Gate" diverter, that can move sideways, to allow more water to strike the wide blades, to , in effect, generate more power as efficiently as possible. I may not use that feature. I won't have the battery system large enough to accept a powerful charge. I want max about 250-400 Watts going to the batteries. This is a 12V, later maybe 24V system, pushing the AC V up to the rectifiers at the battery location.
Any other info you want, just let me know. I'm nearly ready to start building the turbine, and, waiting for magnets from microwaves for the alternator.