Frequently Asked Questions - Hydro Electric

Q.   How much power can I generate with a hydroelectric turbine?

A. The amount of power available depends on the dynamic head, which is a combination of the amount of water flow and the efficiency of the turbine generator.  To get an idea about available power in watts, multiply the head in feet (total vertical drop), times flow in gallons per minute, times 0.18, times turbine efficiency. (For a rough estimate, use 30% efficiency for the turbine, see FAQ concerning efficiency below.)

Q.  How much water and pressure do I need for a small hydro system to work?

A.  In general, the more the better. Practically, you need at least 3 feet of fall with a 12 gpm water flow.  If you have higher fall (pressure), you can get by with much less water.

Q. Can you help with sizing?

 A. Yes, if you think you have a suitable site, contact us and we will help you choose the best unit for your situation.  We will need to know the following information about your site:

1. Head: The total vertical elevation from the place where the water enters the pipe to the point where the turbine will be located.

2.  Flow: The number of gallons per minute that are available.

3.  Distance:  The length of pipe that will be necessary to carry the water from the pickup to the turbine.  If the pipe is already installed, what is the type and diameter?

4.  Location: Distance from the turbine to the batteries.

Q.  What is turbine efficiency?

A. Turbine efficiency ranges from 25% to 50%, with higher efficiency at higher heads.  The Harris Pelton turbines are well suited to higher head and lower flow situations.  Flow is limited by nozzle size (a maximum 1/2").  With the Harris, adjustment to variable flows is as easy as switching a valve and dialing in the alternator. Harris turbines are now available with permanent magnet (PM) alternators. This option provides up to 50% efficiency.  Higher flows are accommodated by the ESD Turgo Turbines. They can have nozzles of up to 1" diameter, and provide better efficiency at low heads.

The HI-Power Hydros are ideal for sites where water is available at long distances from power needs. They generate 100+volts AC that is stepped down and rectified at the batteries. This allows the use of relatively small wire for a distance of up to 10,000 feet. Transmitting the power from the generator to the battery at twice the battery voltage allows you to use 1/4 of the wire size for the same power loss.  At 4 times the battery voltage, you can use 1/16 of the wire size required to transmit power at the battery voltage.  The HI-Power hydroelectric generator can also deliver up to 3600 watts where higher power is needed. The LV Hydroelectric Generator and the ES&D Water Baby are good solutions for very low flow situations where the head is high enough to make some power.

Q.  What size and type of pipe do I need?

A.  Polyethylene pipe can be used for pressures up to 100 psi, PVC pipe is available with pressure ratings from 160 to 350 psi and steel pipe can withstand 1000 psi or more.  Check with your local plumbing supplier for pipe ratings.  Pipe diameter is very important.  All pipelines will cause the water flowing in them to lose some energy to friction.  The pipe must be large enough for the maximum quantity of water it will carry.

Q.  How do I determine how much pressure I have?

A.  A hydroelectric turbine operates from the pressure at the bottom end of a pipeline.  This pressure, usually measured in pounds per square inch (psi), is directly related to the head, the vertical drop from the top of the pipeline to the bottom of the pipeline where the water goes into the turbine.  The pressure at the lowest point of a pipeline is equal to 0.433 times the head, (the vertical distance in feet).  Pressure is important because it is a determining factor in how much power is available and what type of pipe is required. 

Q.  If I know the total head, how can I translate this into pressure.

A. The basic formula is 2.31 psi = total head. Since you know the head, just divide by 2.31 for a psi (pounds per square inch) figure.

Q.  What is dynamic pressure and static pressure?

A. The pressure at the bottom of a pipeline when water is not flowing is called static pressure.  When water is flowing through the outlet or nozzle of the hydroelectric turbine, the pressure at the outlet is the dynamic pressure or running head.  If you install a gate valve on the pipeline just above the turbine and a pressure gauge on a "T" fitting just above the gate valve, you will read the static pressure on the gauge when the valve is closed and the dynamic pressure when the valve is opened.  The maximum power that can be delivered by a pipeline will occur when the dynamic pressure is approximately 2/3 of the static pressure.

Q.  What will be the actual flow rate of the water?

 A. The actual flow rate of the water in a hydroelectric system is determined by the diameter of the nozzle.  We can supply a turbine with the proper size nozzle for your site, depending on the head, flow, length and diameter of the pipe. 

Q.  How do I select a nozzle?

A.  Power out of a hydroelectric generator is determined by the pressure of the water at the nozzle and the amount of water flowing out of the nozzle.  The larger the nozzle, the greater the flow.  The nozzle must also be sized small enough to keep your pipeline full and keep the speed of the water in the pipe below 5' per second.  The nozzle selection chart below shows water flow through various size nozzles at given pressures.  Use this chart to determine what size nozzle and how many nozzles you need to accommodate the flow of water you have and to deliver the amount of power you need.  A pressure gauge in the pipe feeding your turbine, installed before the shutoff valve, can help you check proper operation and diagnose problems.  When the valve is shut off, the gauge will read the static pressure in pounds per square inch psi (head in feet x .433).  When the valve is turned on the gauge will read a lower (dynamic) pressure.  The difference between these two pressures represents your loss to friction in the pipe.  The greater the flow, the greater your loss.  (See PVC pipe loss chart below).

Q. When the hydro site is located more than 300 feet from the house, is it better to use a higher voltage, AC system?

A.  If there's lots of water power available, and the alternator rpm changes relatively slowly, it seems better to send well-regulated 120/240VAC, with the shunt regulator inside the house, with a lightning arrestor in series, but no batteries or inverters, and use the excess power for heating water, etc. Some water wheels are more controllable than others. A Pelton wheel with no load might run 6 times faster than under full load, but other types might only run 20% faster.

Charts will be added soon!  In the meantime, feel free to call or email with your questions.