Power in kilowatts can be determined by the following equation:
kW = H x Q x 62.4 x 0.746 ÷ 550 x e
H = head, in ft.
Q = flow, in cubic ft. per second
62.4 lbs. = weight of 1 cubic ft. of water
0.746 kW = 1 hp
550 foot-lbs./sec. = 1 hp
e = an overall efficiency factor* (usually 0.5 for small microhydro systems)
Combining and reducing all these factors results in the following equation:
kW = H x Q ÷ 24, when using cfs; or
W = H x Q ÷ 12, when using gpm
*Note that the efficiency factor can range from 9 for larger AC systems to 13 or more for smaller battery-based systems, and will need to be estimated for your specific site.