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Sizing a Microhydro System

If you are blessed to have flowing water on your property, you may benefit from a micro‐hydro system that can provide power 24 hours a day.Water turbines steadily charge 12, 24, or 48 volt batteries, working around the clock. Compare this with solarm odules that are in sunshine for, at best, six full‐power hours a day, and that’s just on sunny days. A hydro generator producing 10 amperes around the clock matches the usable power generated by over 40 amps of solar modules. Micro‐hydro is one of the most cost effective and reliable forms of renewable energy, but planning and site considerations can make the difference between success and failure. Late winter into early spring is a great time to start the planning process as snow begins to melt and water begins to flow into the foothills.

The amount of power that your system will generate is dependent on the head, the amount of waterflow, and the efficiency of the turbine generator. The head is the vertical drop over the distance of pipe to be utilized. Head correlates with water pressure available since every 2.31 feet of vertical drop equals 1 psi. Flow is measured in gallons per minute (gpm). These variables will change throughout the stream, so it’s a good idea to take several measurements from areas that you are comfortable tapping, or are allowed to tap for energy production purposes.  A calculation to figure the available power in watts follows: Multiply head in feet, times flow in gallons per minute (gpm), divided by 13.


Components to a Hydro‐System

Intake: This is the area of the stream where you are beginning the pipeline or penstock for the system. The intake should utilize either natural elements of the stream, or a dam to direct the streams flow into the pipeline.  Utilizing the narrowing of a stream, and building up rocks will allow a more natural look to your system without disturbing the existing ecological elements. A place where the stream drops naturally, is stable and would not alter its course overtime is ideal. A screening product should be utilized to prevent debris from entering the pipe. 

Pipe or Penstock: This is the “fuel line” of the system. It is critical that the pipe is sized to minimize friction and “pipe loss”. Too small and you lose potential energy, too large and you are spending excess money for no significant gain in energy produced. There are many choices of pipe types; PVC, steel, HDPE, etc. The walls thickness determines the amount of pressure the pipe can handle before failure.  What you choose will depend on your site, the amount of pressure required, the length of the pipeline, what is available locally, friction losses, and most important; budget.

Turbine: This is the “engine” of the system. There are many different turbines available, each designed for different site considerations.  Backwoods has many techs that are very experienced and can guide you through choosing the right turbine for your site. Turbines are available with different nozzle choices which can regulate the flow during periods of time when the stream’s flow changes due to the season. Turbines include a “runner” or wheel that utilizes the water’s kinetic energy to drive the alternator which generates the power.

PERFORMANCE DEPENDS ON THE SITE more than on the cost.  Greater water pressure at the nozzle, produced by more head (elevation change from the top end of pipe to the bottom), brings more power.  Greater water volume (gallons per minute) onto the wheel can also bring more power.  Sites with higher head are most desirable because they need less water, smaller pipe, fewer nozzles, cost less to install, and fare better in low water years.


System Types

Stand‐Alone system with batteries: This system is very similar to an off‐grid solar or wind system where the renewable energy source is charging batteries or a generator system that charges a battery bank. In addition, you will need a controller to protect the batteries from overcharging and a diversion load to accept excess energy when the batteries approach full charge.

Battery based grid‐tie system: This is very similarto the above example, you will still need the additional components listed, but they will only be used in times of a power outage. When the grid is on, grid‐power will take the lead in charging and regulating the batteries and any excess power generated by your hydro system will be back fed into the grid, reducing your electric bill.

Batteryless grid‐tied system: Systems of this type use a turbine and controls to produce electricity that can be fed directly into utility lines. These can use either AC or DC generators. AC systems will use AC generatorsto sync directly with the grid. An approved interface device is needed to prevent the system from energizing the grid when the grid is out of action and under repair.  DC systems will use a specific inverter to convert the output of a DC hydro turbine to grid‐synchronous AC. The biggest drawback of battery-less systems is that when the utility is down, your electricity will be out too. When the grid fails, these systems are designed to automatically shut down.

Let us help you!

Pipe size, number and size of nozzles and choice of alternator depend on measurements of your site. Since there are so many combinations of water volume and head, it is best to contact us and describe your creek site. Tell us specifically:

  • What elevation change (from intake to the turbine) over the length of the pipe?
  • How many gallons per minute flow, minimum and maximum?
  • What size, type, and length of pipe (if it is already installed)?
  • Wire distance from hydro plant (lower end of creek) to the home or powershed?