Site Evaluation Guide

Do I have A Viable Hydro Site?

This is a complicated question. The answer depends mainly on physical properties like head and volume of water available, pipe losses and wire transmission losses. The cost of pipe and wire can sometimes kill a project. There can also be environmental concerns as well as political stuff like water permits. Hydro is probably the least expensive of the three major renewable energy resources. Entry level systems can be done for $2000 but most will be higher. Most of the hydro applications we do are for residential scale off-grid battery based systems. Grid-tie is also possible but AC direct hydro requires a much larger resource than what most people have for a creek or stream. Regulatory obstacles are more common with the larger streams as well, especially if they are fish bearing. Hydro works well in conjunction with solar and wind systems so there is no need to lock oneself into a mindset that the hydro has to produce all your power needs since the creek will likely have an upper power potential that can’t be changed without altering the laws of physics. Stream flows are almost always highly variable during different times of the year and also from year to year. In short…you get…. what you can get.

Definition of some commonly used terms


This is the vertical component or elevation change between the intake or point of diversion and the hydro electric generator. We prefer measurements in feet or pounds per square inch PSI because metric still does not fit inside our heads.

1 PSI = 2.31 ft of head.     1 ft. of head = .433 PSI.     1 meter = 3.28 ft.


This is the quantity of water actually put thru the nozzles. Leaks don’t count for power production. Most residential size systems measure the flow rate in gallons per minute GPM . Larger systems typically use cubic feet per second CFS

450 GPM = 1 CFS   also 1 cubic ft. = 7.48 gallons.   3.78 liters = 1 gallon US

Static Head

Head measured at 0 flow rate or resting pressure. No work is being done.

Dynamic Head

The net head under actual working conditions. This # will always be less than the static head and is a result of losses in the penstock mostly due to friction.


A somewhat all inclusive term to describe everything in the piping system from the intake to the nozzle at the turbine.


The focusing pipe at the end of the penstock at the turbine that directs a precise stream of water at the Pelton wheel. We use an interchangeable jet at the end of the nozzle for flow control on our units.

Pelton wheel

The water runner or cup shaped wheel that the nozzle sprays into that turns the generator. Doble actually perfected the Pelton wheel but receives almost no recognition. The latest computer programs have only increased the efficiency of Doble’s design a few percentage points since the early 1900’s.


This is a unit of electrical force similar to pressure in a pipe.


This is a unit of electrical current or volume or flow rate.


This is a unit of power and is a product of amps times volts. 4 amps at 12 volts = 48 watts assuming a power factor of 1.0


Or Kilowatt hour is a thousand watts over an hour. 1.5 KWH for 5 hours would be 7.5 KWH. A hydro generating 500 watts for 24 hours = 12 KWH/day. Your utility power bills usually show average KWH per day and total for the month for comparison. Energy efficiency and conservation is the best place to start if you are looking for the best value. Americans waste power with a vengeance. This is a short sighted “attitude” with planetary consequences. Solar, Wind and Hydro are recycled energy resources driven by the sun with a net heat gain of zero unlike petroleum and coal.


Amp hours. Since we are dealing with the DC side of the system most of the time, I find it easy to think in terms of amp hours used or replaced. If the power system used 120 AH/day it would take a hydro running at 5 amps for 24 hours to replace it assuming the battery system is 100% efficient. Lightly cycled systems can be 99% efficient but most are around 94% for hydro use. Solar and wind based battery systems can be around 80%. Most systems are hybrid versions of solar and hydro or ? so this figure will be unique to each.