Components: Penstocks

Friction in the pipe (penstock) or open channel that carries water to the generator is another cause of power loss. Most small hydroelectric sites have a small or moderate head, so it is very important to use large penstocks to reduce losses. 

If you are diverting a water source far up the hill, plastic or aluminum irrigation pipe and the heavier walled, pressure rated PVC plastic pipe make good penstocks. Table 2 shows head losses for typical plastic pipe. The flow rates to the right of the dashed lines have velocities that exceed 5 to 7 feet per second and are not recommended. Use a larger pipe instead.

For example, Table l shows a 2KW generator requires 0.6 cfs with a l00 foot head. Three hundred feet of 3" PVC pipe carrying 0.6 cfs from an upstream diversion has a head loss of 3 x 10.2 = 30.6 feet. Thus the diversion must be 100 + 30.6 = 130.6 feet above the generator to compensate for the friction or head loss in the pipe. A 6" pipe has only a 0.54 x 3 = 1.62 foot head loss.