Micro Hydro Power

off grid power Nov 10, 2020

If you have the desire to live off the grid, one of the first considerations should be how you plan on powering your life. Even if you have no desire to live off the grid, you should still consider having an alternative source of power. When it comes to homesteaders and off grid folks, most settle on some sort of renewable energy system. As you probably already know, there are several potential options for powering your home.  The most common options are solar, wind, and micro hydro.  

At first the concept of renewable energy my seem very simple.  After all, how difficult can it be to put up a few solar panels and charge some batteries? Right? The truth of the matter is that it depends. If you want to power a few lights, then the whole process is very simple. However, if you want to power an entire home, that is a different story altogether. 

I use to think along these same lines until I took some advanced classes on renewable energy. As a result, I then returned home to design and install my own solar electric system. Shortly thereafter I found it to be far more complicated than my former way of thinking.  The same is true for a micro hydro power system. It depends. Small scale is very simple. Powering a home is a different story. 

The good news is that renewable energy systems share many similar components. However, a micro hydro power system does have some special considerations. Furthermore, it is not as simple as submerging a turbine in flowing water and having instant electricity. Just as with other forms of renewable energy, a successful micro hydro power system requires some careful planning. 

Here is what you will learn in this post:


How Does a Hydro Electric Power System Work?

When most people think of hydroelectric power, they immediately envision an enormous damn and reservoir system. These systems are capable of generating billions of kilowatt hours (kWh) per year. However, small scale hydro electric power system, often termed micro hydro, generates from 5 kWh to 100 kWh. Consequently, such systems are within reach of the average person. 

Very simply put, micro hydro systems use the power of gravity to generate electricity. As water flow travels downward, it is diverted into the micro hydro system. The gravitational force of the water drives a turbine which then turns a generator that produces electricity.  There are several different ways to achieve this result. 

Use the existing flow of a stream or river: In this system, the flow of water is simply directed through a submerged turbine. Since there is no river or stream diversion involved, this is the simplest form of micro hydro. However, it has the distinct  disadvantage of being entirely dependent on the flow of the water. If water flow decreases so does the power production. Despite this disadvantage this is the most common form of micro hydro power used for household or community systems because of the simplicity. For example, in extremely small systems, a submersible turbine can be placed in as little as 13 inches of flowing water.  

Dams and reservoirs: This is the most common form of commercial hydropower and is for large scale production.  A reservoir stores the water, which is slowly released and diverted through the turbines.  Even if the flow of the river declines, the energy production remains constant. 

Pumped storage system: Off peak electricity, which is less expensive, is used to pump water from a river or lower reservoir into a higher reservoir. The water is then released and diverted through a turbine to produce electricity. 

Is  Micro Hydro Power A Feasible Alternative for Me? 

As with any other renewable energy system, there are numerous factors to consider before spending any money. The first step is to perform a proper site assessment. This assessment is crucial to determining if a micro hydro power system is even feasible for a given location. If the assessment is favorable, you then have to factor the economics, water rights, and proper permits involved in setting up your system.

The critical part of site assessment is determining head and flow. These two factors are directly related to energy production. Additionally,  seasonal water flow also has to be taken into account as this affects total energy production throughout the year. The water flow in rivers and streams varies greatly throughout the year. Typically flow is lower in the summer months. The time of year with the lowest water flow is critical to the design of the system because it affects the economics and practicality of the system.    

Any renewable energy system is going to have variations in the amount of energy production.  This is true for wind and solar as well.  The wind does not blow at a consistent pace, the sun does not shine 24 hours a day, nor does the water flow in any stream or river stay consistent 365 days per year. This is the reason that the lowest energy production month of the year for any renewable energy system is critical.  Let’s take solar as an example.  

For most locations in the northern hemisphere, January is the month when the sun is lowest in the sky and day light hours are the shortest.  Consequently, this is the time of year when energy production for a solar array is at its lowest. This is called the critical design month. The system needs to be designed to meet your energy needs even during the times of the year when energy production will be at the lowest. Consequently, if designed properly, the system will consistently provide adequate  energy throughout the entire year.   

The same is true for a micro hydro system.  The time of year when water flow is at its lowest point is the critical design month. Consequently, the system must be designed to meet your energy needs based on that particular month. 

Provided all of the above factors are met then a micro hydro system is a practical and economic choice.  Now let’s move onto some other basic information.  

The Basics of a Micro Hydro System

(The illustration below is credited to energy.gov and can be found in their article titled MicroHydroPower Systems

Many components in renewable energy systems are very similar. All of these systems require transmission lines, inverters, charge controllers, batteries, load boxes, etc.  But some components are very specific to hydroelectric systems.  The following is a list a standard components for any micro hydro system:

  • Access to consistently flowing water with enough force to power the turbine
  • Turbine and alternator properly housed from bad weather
  • Proper water intake and sufficient pipeline (penstock) to divert water into the turbine and return it to the stream
  • Battery bank to store energy
  • Charge controller for the battery bank
  • Electrical lines to carry power to the point of use
  • Power inverter to convert the electricity to alternating current (standard household current) 
  • Proper permits

Now that we have covered a good introduction to micro hydro, let’s move on to some more specific information as far as actually designing a system.  The critical first step is site assessment. 

Site Assessment

Obviously to make a micro hydro power system work you need direct access to flowing water on your property. Provided that is in there, to determine if such a system is feasible, it is necessary to calculate two factors: 

  • Head: the vertical distance that the water flows
  • Flow: the quantity of water falling or flowing

Once these two things are determined, you can use a simple equation to determine your potential power output.  Most renewable energy systems are about 50% efficient and the same holds true for micro hydro power. The equation is as follows: 

[ net head (feet) x flow (gpm) ] ➗ 10 = Watts produced

Watts produced x 0.5 (50% efficiency) = total energy production

Determining “Head” 

Simply stated, “head” is the vertical distance that water falls. Head is usually measured in feet, meters, or units of pressure.

Additionally, head is affected by the channel or pipe through which the water flows. Pipe diameter, curves, bends, or any angles in the pipe causes friction which slows down water flow. This reduces the effective head produced at the other end.  

Higher head means greater water force. The greater the force of water, the greater the force on the turbine and the greater the energy production. With a higher head less water flow is needed in order to produce electricity. High head also means you can use smaller less expensive equipment. Low head is referred to a drop of less than 10 feet.  Anything less than 2 feet essentially makes a micro hydro system unfeasible. 

What this means is that in order to make a micro hydro system feasible you need either high head with low flow or low head with high flow. An additional alternative, sometimes referred as a “zero head” system, is to use a submersible turbine. Some of these turbines need as little as 13 inches of water. But, keep in mind that this is only going to work for extremely small systems. These types of turbines are referred to as “jack rabbit” turbines.  

Gross head measurement 

Gross head is the total amount of vertical drop for the stream in question. This measurement is taken between where the water enters the penstock (piping) and where the water discharges from the turbine and back into the stream.  

The most accurate way to determine gross head is with a professional survey. It is also possible to get a rough estimate from geological survey maps.  However, another practical means of determining gross head is the hose and tube method.  

Hose and tube method is as follows: 

  • Equipment needed is a 20 to 30 foot (6-9 meters) length of small diameter flexible tubing or garden hose, a funnel, a yardstick or tape measure.
  • Start taking measurements from the point where the entrance of the penstock will be located.
  • Place the funnel in the upstream end of the hose and stretch the hose down the stream channel.
  • Submerge the funnel just below the surface of the water so that water will enter.
  • Lift the downstream end of the hose out of the water until water stops flowing.  
  • Measure the vertical distance from the downstream end of the tube and the upstream surface of the water.  This is the gross head for that section of the stream.
  • Now move the funnel to the point where the first measurement was taken and repeat the process until you reach the point where the turbine will be located. 
  • Add the vertical distances of all measurements for the total head.  

Direct measurement method:

This is by far one of the most accurate methods. It involves using laser level, a surveyor’s transit, and a contractors’s level on a tripod.  For an accurate description of this method, go here. 

Water pressure method

Each vertical foot of head creates 0.433 psi of water pressure. Thus, by measuring the water pressure at the bottom of a hose, you can accurately measure the vertical drop or head. This requires running a hose from the penstock intake to the turbine site.  If you connect multiple lengths of hose, make sure the fittings are leak proof. The hose should be flushed with water to remove all air bubbles.  

You can also do this with shorter sections of hose. However, the margin of error increases significantly with a series of low water head readings. It is far more accurate to use the longest hose possible. Additionally, it is imperative to use a very accurate pressure gauge.  

If done correctly, this is one of the most accurate and simple methods for measuring gross head. 

Net head measurement

As water flows through a pipeline, the friction of that flow slows down the force of the water. The loss in water flow is related to multiple factors such as pipe diameter, as well as bends and curves in the pipe. Because these factors slow down the force of the water it has the same affect as reducing the head. Net head  is a more accurate measurement of potential power output.  

For a great explanation of net head measurement, visit this     Guide to hydropower.     

Determining Flow

The flow of a water source is typically recorded as a measure of volume per second or minutes.  Examples of this wound be gallons /second, gallons/minute or cubic feet per second or minute.  There are a few different methods to determine flow. But the most common are the container fill and float method. 

When determining flow, keep in mind these common conversion factors.  

Common conversion factors are as follows: 

  • 1 cubic foot = 7.481 gallons
  • 1 cubic meter = 35.31 cubic feet
  • 1 cubic meter = 1,000 liters Container fill method

Container fill method

This is the most common method for determining flow for micro hydro systems. It is quick and simple.  For the stream that is being measured, find a point where all of the water flows through a single outlet.  If this is not possible, build a temporary damn.  Take a container of known volume and use a stop watch to record the time it takes to fill that container. 

For example, if it takes 5 seconds to fill a 5 gallon container, your flow is 1 gallon/second. If it takes 10 seconds to fill a 5 gallon container then your flow is 0.5 gallons/sec. 

Float Method

This method is useful for larger streams. This task will be much easier if measurements are taken in an area of the stream that is approximately 10 feet long and is fairly consistent in width and depth.  

Step 1:

Place a board, log, or string across the width of the stream. Mark your device in one foot increments. Measure the depth of the stream at each increment. Add all depth measurements together and divide by the number of measurements taken.  This will give you average depth. 

Step 2: 

Compute the cross sectional are of the stream.  Multiply stream width by the average depth determined in step 1. For example, an 8 foot wide stream with an average depth of 2 feet gives you 16 square feet. 

Step 3

Measure the speed of the water flow.

Measure out a 10 foot length of the stream in question. Include the area of the stream where cross sectional measurements were taken.  Place a brightly colored weighted float in the stream well above your area of measurement.  This will allow the float to be at a consistent speed once it enters your area of measurement. Stream speed will vary across its width. Consequently, it is more accurate to take several measurements and then take the average. 

Record the time it takes for the float to travel through your area of measure. Divide the distance by the time to get flow velocity in feet per second.

Step 4

Multiply the average velocity by the cross sectional area of the stream. This will give you cubic feet per meters or per second/minute depending on your unit of measure.  

Example calculation for a micro hydro system

  • Net head = 50 feet
  • Flow rate = 250 cubic feet /minute
  • Conversion factor: 1 cubic foot = 7.481 gallons
  • 250 cubic feet/minute  x  7.481 gallons = 1,870 gallons/minute

From the equation listed above: 

  • [ net head (feet) x flow (gpm) ] ➗ 10 = Watts produced
  • Watts produced x efficiency of the system = net energy 
  • 50 x 1870 / 10 = 9,350 watts x 50% efficiency = 4,675 watts produced. 

Basic Economics of a Micro Hydro System

In the United States the cost of electricity varies according to the state where you reside. Therefore, it is important to look at what you pay for electricity from your local service provider as a means of comparison. 

To find this information, look at this chart of the cost of electricity by state provided by   Electricchoice.com

Personally, just because I am fiercely independent, I would install an alternative source of electricity regardless of the cost. This is just a means of personal security. However, it is extremely valuable to have a means of comparison. Consequently, you need to know the cost of electricity per kWh from your service provider. Then compare that to what it would cost for an alternative energy system such as solar, wind, and hydro.  

Once you determine you potential power output from your micro hydro system, then you can determine if it is economically feasible.  Also, since you have already read my post of ways to save electricity, you already know that it is easier to save electricity than it is to produce it.  

Now let’s talk dollars. Add up all of the estimated costs of developing and maintaining your hydro electric system over the expected life of the equipment. (Most equipment will last at least 25 years.) Divide that cost by the expected energy output of the system during that time frame.  This will give you a cost per kW/hr for the energy produced.  

Now compare that figure to what you pay for electricity from your service provider. Additionally, compare that to the cost of  producing the same amount of energy from solar and/or wind. This will tell you if a micro hydro electric system is economically feasible. 

In addition to this, there are potentially a variety of financial incentives for investments in renewable energy systems. These can come in the form of income tax credits, loan programs, grants, property tax exemptions, as well as sales tax exemptions. These incentives can go a long way toward offsetting the long-term cost of a renewable energy system. 

Water Rights and Permits

It is imperative to investigate local permits and water rights when it comes to installing a micro hydro system.  Even if the system will be solely on your property, you still need to obtain permission before diverting any water from a particular channel.  

Generally speaking, the permitting process will be easier if you are not connected to the grid or you do not plan on selling electricity to the local utility company. Each state varies considerably on this whole process.  However, if you are using a local company for design and installation, they will likely have connections to help you through this process.  Otherwise, read this article on Planning for Home Renewable Energy Systems to get a good idea of this whole process.  

And last but not least, let’s talk a little about the advantage and disadvantages to a micro hydro power system. 

Advantages, Disadvantages, and Limitations of Micro Hydro power


Cost effective: Small scale micro hydro can cost as little as $1,000. A system large enough to power several homes may cost as much as $20,000. However, if this were a community development project, the cost would be spread out over several families. 

Maintenance costs are generally low. 

Reliable: Micro hydro provides a continuous source of electricity. Peak production is in the winter months when electricity requirements are higher. 

Small scale production is possible: Electricity can be produced with as little as 2 gallons per minute of water flow or as little as a 2 foot drop. 

Little environmental impact: No reservoir is required. Micro hydro functions as a so called “run-of-river” system. Water passes through the generator and is directed back into the stream. There will be some small impact on the local environment during construction.  However, with small scale systems, this impact is minimal. 

Pollution free: Unlike the burning of fossil fuels, generation of electricity with micro hydro produces no pollution. The fuel source is simply the flow of water.  

Fantastic off grid power source: Because of the reliability of micro hydro systems, they are a great alternative energy source. These systems are more reliable than the local power grid. 

Flexible, on demand power source: As with other renewable energy sources, power generation can be turned on and off, or adjusted as needed. 


Site characteristics are very specific: Not every location is suitable for this source of power. You must have suitable water flow rate, and drop.  The site of energy production must be reasonable close to the point of use.  If not, the cost of installation will be much higher.  

Expansion may be limited or expensive: As your energy demands increase, it may not be possible for you to expand your present system.  Or it may be very expensive to expand your initial system. 

Power generation will fluctuate: Power production is lowest in the summer months because this is typically when stream flow is lowest. Consequently, you must plan accordingly.

The intention of this post was to give you a basic understanding of micro hydro systems. If you are serious about using this type of renewable energy system, the refer to the resources below for some great detailed information.

Additional Resources:

 Planning for Home Renewable Energy Systems

 Planning a Microhydro System

 Mircohydro: Clean Power from Water

 Design Considerations for Micro Hydro Electric

 Homestead Power

 Hydropower Basics

 Guide to Hydropower

Additional Posts of Interest

35 Ways to Save Electricity

Introduction to Renewable Energy Systems

23 Reasons to Choose Solar Power


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