Micro Hydro Electric

by Bryan A. Thompson

Last Updated 2/12/2003

 

Note:  This stuff is all from the WindStream Power Systems website - the only place on the web I found this sort of information.  Eventually I'll get around to doing more research on this subject and replace this with original material.  Until then this information can be used to compare Hydro power to other alternative energy sources.

 

Overview

Small hydroelectric generators that are designed to be 12, 24, or 48 volt battery chargers, operating off a relatively small volume of water. They charge batteries 24 hours per day and the power can be drawn from the battery as needed. As little as 100 gallons per minute (GPM) falling 10 feet through a pipe or 5 gallons per minute falling 200 feet through a pipe can supply enough power to comfortably run a small household. In areas where there is a long rainy season, and there is a mountain stream that can be used, a small hydroelectric system can work well with solar modules, both charging the same battery. When it is rainy and the solar modules are putting out less power, the hydroelectric system will be at its peak.

By contrast, typical AC power hydroelectric systems, designed to deliver ready-to-use 120/240 VAC power, are not practical for most people because they need a constant water supply large enough to supply the peak power output that will be required, usually a minimum of several thousand watts, requiring hundreds or even thousands of gallons per minute, depending upon the pressure available. Besides requiring large amounts of water, these turbines require large pipe diameters and expensive regulating systems that can maintain proper frequency and voltage at all times.

 

How much power can you generate?

The amount of power available depends on the dynamic head, the amount of water flow and the efficiency of the turbine/generator combination. To get an idea about available power in watts, multiply the head in feet, times flow in GPM, times 0.18 times efficiency. Turbine efficiency ranges from 25% to 50%, with higher efficiency at higher heads. To get a rough idea, use 0.30 (representing 30%) as a multiplier for efficiency.
 

HOW TO CALCULATE THE POWER AVAILABLE FROM A HYDOELECTRIC GENERATOR

1. Measure or Estimate the Head (H):

The head is the vertical difference in level between the source of water and the turbine, measured in meters. (If the data is in feet, multiply by 0.305 to convert to meters).

2. Measure the Flow Rate (Q):

The flow rate is the volumetric rate at which water enters the turbine, measured in liters per second. (If the data is in cubic feet per second, multiply by 23.8 to convert to liters per second, if in gallons per minute, multiply by .063). One way to obtain an approximation of the flow rate is to throw a buoyant object into the middle of the stream, and time its travel in seconds over a known distance in meters. Then multiply by the estimated cross-sectional area of the stream, in square meters, and divide by 1000 to obtain the flow rate in liters per second.

3. Estimate the Overall Efficiency (E):

Efficiency is expressed as a non-dimensional decimal: for instance, E = 0.54 would mean that the system is 54% efficient, or that 54/100 of the incoming energy is actually being delivered to the load. To estimate the overall system efficiency, multiply the individual efficiencies of each part of the system: for instance, if the intake pipe efficiency (due to friction losses from the inside walls of the pipe) is 0.94, the efficiency of the actual water turbine is 0.74, and the generator efficiency is 0.77, and if there is no back pressure at the outlet of the turbine, then the overall system efficiency would be E = 0.94 X 0.74 X 0.77 = 0.54. If you don't know any of this information, or don't want to calculate it, the typical efficiency rating is 50% (E=0.5).

4. Calculate the Available Power (P):

Calculate the power in watts, using the figures obtained above, in the following formula: P = 9.8 Q X H X E watts
For example, if the head H = 10 meters, the flow rate Q = 5 liters per second and the system efficiency E = 0.5 (i.e. 50%) then the available power P = 9.8 X 10 X 5 X 0.5 P = 245 watts

To express the power in kilowatts, divide watts by 1,000: 245 watts = 0.245 Kw.
To express the power in horsepower, divide watts by 746: 245 watts = 0.384 hp.

5. To Calculate Annual Energy Production:

To obtain the annual energy production of the system in kilowatt-hours, assuming continuous operation, multiply the power in kilowatts by the number of hours in a year (8,760). In the above example, the annual energy production of the system would be 0.245 X 8,760 = 2,146 kilowatt-hours per year. To express this figure in megawatt-hours per year, divide by 1,000: 2,146 KWH/year = 2.146 MWH per year.

 

Pipelines

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, or vertical distance from where the water goes into the pipe at the top of the pipeline, to the turbine located at the bottom of the pipeline. The pressure at the lowest point of a pipeline is equal to 0.433 times the vertical distance in feet, called head. Pressure is important because it is a determining factor in how much power is available and in what type of pipe is required. 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 you 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. 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. The actual flow rate of the water in a hydroelectric system is determined by the diameter of the nozzle. We will supply a turbine with the proper size nozzle for your site, depending on the head, flow and length and diameter of the pipe.
 

Where To Buy

WindStream Power Systems - They sell MicroHydroElectric products that are capable of charging 12V batteries.