The formula as I understand it is:
power (watts) = pressure (psi) x flow rate (gpm) / 2.3
Assumptions:
10 gpm at 40 psi (pick new ones if you like, I had to start somewhere).
Assume whatever power system you have is 50% efficient.
$0.10 per kwh
power output = 10 x 40 / 2.3 x 50% = 87 watts
dollars saved per hour from electricity generated = .087kw x 1 hr x $0.10 =
$.0087 / hr (or 0.87 cents per hour)
This is from 600 gallons / hr flowrate.
If you use 10,000 gallons of water per month, the generator will run for about 17 hours per month, netting you a cool 15 cents.
Somebody please check my math,
-Dan M