An overshot wheel is a system that uses dead weight as a motive force, while the overall velocity and volume are important the
work is accomplished by little more than weight.
An undershot wheel uses velocity and surface area as its motive force.
A Pelton turbine uses velocity and pressure to move, its tailored to a specific load at a specific pressure.
For heavy work as a prime mover nothing beats an overshot wheel if you have adequate flow,
Generators need to be geared to make up for the low rotational speed or manufactured to low speed standards, but an overshot will act as prime mover for sawmills, gristmills, lathes, or any other heavy application.
An overshot wheel can be built by any competent
wood worker or fabbed from aluminum or sheet steel. The taller the wheel the more torque, the larger the bucket the more torque depending on the streams ability to fill it.
Undershots are a desperate compromise when there is inadequate fall of the
land. Still beats paying for power!,
Once again the taller the wheel the more torque, and the larger the surface area of the sails the more torque.
Pelton Turbines are a highly engineered solution, just
enough for the required load, wonderfull machines but near impossible to repair with low tech / 3rd world resources, best options are nut and bolt replacements, and buy spare parts when your wealthy cause they
will wear out.
Peltons are easy! Write what you want on the back of a large enough check and some clever guy will deliver it to your door!
Finaly there is a "vortex" system that drops high volumes of water over a very short distance, there are lots of homemade efforts but for reasonable efficiencies they are once again an engineered solution.
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