Micro Hydro Turbines

Micro hydro turbine installations are often located in remote, off-grid mountainous areas.   There must be adequate vertical terrain to provide the drop, or head, for the water to descend naturally.  If the drop is steep, head can be achieved with a short length of pipe.  Shallow grades also work but require longer pipes which contain more friction head.

Micro hydro generation offers a cost effective alternative to solar or wind provided an adequate stream source runs within a quarter mile.  Energy harvested per dollar invested can be one to two orders of magnitude (ie., 10 to 100 times) greater than with solar or wind.   Check out our Micro Hydro Library for a wide selection of books on the subject.

Basic Operation

A micro hydro turbine system draws water from a stream fed pool at the highest point in the system.  The water enters the pipe through a filter that is sized to keep damaging debris out of the turbine.  Pipe diameter and length affect flow rate and the vertical drop defines total head.  Shut-off valving controls water flow through the pipe and the turbine.  After passing through the turbine the water is returned to the stream.

Generic Layout of a Micro Hydro Turbine System

Since streams flow 24/7, electricity can be generated around the clock rather than just when the wind blows or the sun shines.   This reduces the amount of battery storage needed which helps to lower system cost.  If sufficient flow is available, a small home can be powered directly with a micro hydro-turbine using an inverter.

Combining solar PV with a micro hydro turbine system is a viable option to consider if the flow rate of the stream is seasonal.  Stream flow is generally higher in Winter and Spring when more power is required and less sunshine is available.  During the longer sunnier days of Summer, solar can boost available energy when the stream flow slows in the drier weather.

To generate electricity, adequate head in feet (vertical drop of water) and sufficient flow in gpm (gallons per minute) are a must.   The higher the head and/or the greater the flow rate the more power can be generated.  For smaller battery charging systems power is generated at 12, 24 or 48 volts.  Larger systems can generate at 120 or 240 volts.

Since DC (direct current) generators are generally used with micro hydro turbines, the power needs to be converted to AC (alternating current) with an inverter before it can be used to power household appliances.  When planning a system, the inverter should be located in close proximity to the the turbine generator to increase the voltage to 120 or 240 volts.  This higher voltage reduces the current which allows smaller wire sizes to be used to carry the power to its point of use.

This generated energy can be measured with a home energy monitor if an inverter is used.  CT's (current transformers) should be located close to the point of use so any voltage drop over the incoming line will be accounted for.

Metering Alternative Energy Generation with a Home Energy Monitor

System Output

What level of output can be expected from the various sizes of micro hydro turbine systems?

Small systems:
50 feet of head run through 600 feet of two inch poly-pipe will produce about 80 kilowatt-hours per month.  A spring producing 5 gpm dropped 200 feet through 1000 feet of 1.5 inch poly-pipe will produce about 70 kilowatt-hours per month.

Medium Systems:
100 feet of head run through 600 feet of two inch poly-pipe at 50 gpm will produce about 235 kilowatt-hours per month.  Higher flow of 200 gpm through a four inch poly-pipe 300 feet long with only 20 feet of head will generate about 185 kilowatt-hours per month.

Large Systems:
A 900 foot long four inch pipe with over 300 feet of head flowing at hundreds of gpm can produce thousands of kilowatt-hours per month.

How to Calculate Micro Hydro Turbine Output

The first step is to determine the flow rate of the water being diverted from the stream.   For low flow rates, this can be done by timing how long takes to fill a five gallon bucket.   For example, if the bucket fills in four seconds the flow rate would be:

5 Gallons x 60 sec/min = 75 gpm
  4 sec to fill

For larger flow rates, the volume of water flowing through a calibrated wier board can be measured in cubic feet.  Cubic feet can be converted to gpm using the following formula:

1 cubic ft/sec = 450 gpm

We also need to know the pressure generated by the water descending through the pipe which can be expressed with the following relationship:

2.31 ft of head = 1 psi

As a general rule of thumb, micro hydro power for a battery charging system can be estimated as:

Power (watts) = Net Head (ft) x Flow Rate (gpm)
                      14

If the system powers an inverter directly the output is more efficient and can be expressed as:

Power (watts) = Net Head (ft) x Flow Rate (gpm)
                      9

Lets put these equations to work in the following example.  We have 800 feet of pipe dropping 120 feet to power a battery charging system.   Using our five gallon bucket, we found it took 6.0 seconds to fill.   The flow rate is:

5 Gallons x 60 sec/min = 50 gpm
  6.0 sec to fill

Next, determine the amount of friction head.  Friction head is the equivalent loss of actual head, expressed in feet per 100 feet of pipe, that is caused by the pipe's diameter and surface friction of the material in which it is made.

In our example, we are using 2 inch diameter PVC pipe which has a friction head of 2.7 feet per hundred feet of pipe.  Applying this factor, the net head calculates as follows:

Net Head = Actual Head - Friction Head (ft/100 ft) x Pipe Length (ft)
                                       100

 98.4 = 120 - 2.7 x 800
                     100

Using the power formula for a battery charging micro hydro turbine system total power is estimated to be:

Power (watts) = Net Head (ft) x Flow Rate (gpm)
                      14

 351 watts = 98.4 x 50
                       14

At 351 watts per hour, daily output would be about 8.5 kilowatt-hours.  If we assume stream flow remains constant, the generator would deliver about 250 kilowatt-hours per month.

If feeding an inverter to power 120 VAC appliances, the inverter efficiency and voltage drop to the point of use need to be considered when calculating available power.   Monitoring power produced with a home energy monitor system will be most accurate when located close to the point of use.

For a more in-depth discussion about these types of systems check out the Micro-Hydropower Systems Buyers Guide distributed by the CANMET Energy Technology Centre of Canada or visit our Micro Hydro Library.