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Micro Hydro Essentials

by GLI Editors in Micro Hydro Energy

If you’re an alternative energy advocate seeking for ways to green your living and you happen to live by a river or creek, you might be in luck.  We all know energy is generated by building dams over giant underwater turbines, but this technology doesn’t have to be built on such large scales.

Micro hydro generators use modest water flows to generate electricity, and they trump solar and wind power in reliability because water runs day and night, independent of weather situations.  Let’s take a look at a typical hydroelectric power plant to better understand how this technology works…

• How it Works
• Go with the Flow: Calculating Water Flow

• Give it a Spin: Types of Turbrines
• Cost and Installation
• Maximizing Micro Hydro

How It Works

Water is a heavy medium that moves quickly.  Similar to a car, which has similar properties, it takes a lot of energy to get water flowing.  Anyone who has ever stood by a waterfall or gone swimming in the ocean can vouch for the power of water flow.  In a hydroelectric power plant, engineers use the energy stored in running water to generate electricity.

Today, hydroelectric power is the most widely used renewable energy source. It accounts for approximately 16% of worldwide electricity production, far outweighing the contributions of solar, wind, and geothermal combined.

The most prominent feature of a hydroelectric plant is the dam.  Large dams are immense structures, sometimes hundreds of meters high, which can hold back several cubic miles of water.  Since water is the source of energy for a hydro plant, the dam is important for storing and controlling the flow of energy.

• Once the dam is constructed, underwater gates are opened to regulate flow through an underwater turbine.

• The pressure of the water pushes on the turbine blades, causing the turbine to spin a shaft that is connected to a generator.

• Spinning magnets and coils in the generator produce current that is directed through a transformer and out to the grid, where it is used by you and me.

For residential generation, you probably won’t be blocking off a river or storing a cubic mile of water.  Instead, a typical residential generator uses a pipe to collect water from a stream or river.  The water gains energy by flowing downhill and is passed through a turbine that is connected to the end of the pipe.  The type of turbine you will need depends on the type of flow available on your property.

Go with the Flow: Calculating Water Flow

There are two numbers that measure the amount of energy available in your water supply: flow and head.  Before installing a hydropower generator for your house, you will have to determine both of these numbers.  Most hydroelectric installers will help you to estimate these values, but let’s take a look at them to get the general idea.

Flow means just what you think it means—the amount of water that you have available to turn your water wheel or turbine. The more flow, the more energy you can produce.  In terms of a micro hydro generator, it will be the amount of water running down the pipe to your turbine. 

• In one second, how many cubic feet of water can you safely divert from your stream to turn a turbine? To put things into perspective, for a residential application (which typically requires a few kilowatts of electricity):

• a few cubic feet of flow per second is considered an ample flow rate
• a number below 0.1 cubic feet is considered low

Low flow rates can still be used to generate electricity, as long as your water source has enough head.  Remember to consider seasonal changes in water level when estimating flow.
Head refers to the pressure of the water that strikes your turbine blades. To understand the importance, imagine a high-pressure fire hose spraying a water wheel.  Clearly, the pressure of the fire hose would deliver more energy to the wheel than a typical garden hose.

In order to determine your head, you will need to estimate the distance water will fall before reaching your turbine.  The farther the water falls, the more energy you can produce with your water source.

• 
  What is the maximum elevation change between the entrance and exit of a pipe on your property?

• You will need several feet of head for a residential generator, but numbers above 30 ft are best.
• It is important to get an accurate measurement of head before purchasing a hydroelectric system, since this number affects the type of system you will need.

No matter what your head or flow, you will need at least one of the numbers to be relatively high in order to operate a generator for your home, and you will need both numbers to satisfy minimum criteria.

Calculation:  To approximate the number of kilowatts that will be generated using your water source, multiply head by cubic feet per second, and divide this number by 7.  (Note that this is a rough estimate, and results may vary greatly due to factors not taken into account in this calculation).  Contact a micro generation company to get a more precise estimate.

Give it a Spin: Types of Turbines

Now that we’ve determined our flow characteristics, we can start shopping for hydro systems.  The most important part of your residential micro hydro plant is the turbine, where flow energy becomes rotational energy.  Although they come in many shapes and sizes, there are two main types of turbines.

A reaction turbine is the type used in most commercial hydropower plants, and it operates underwater.  The change in pressure as water flows across the device pushes on the blades and causes the turbine to spin.  The snail-shaped Francis turbine and the Kaplan propeller are both examples of reaction turbines.  These turbines must be fully enclosed to preserve water pressure, and are used in low-head systems with high flow.

Impulse turbines, on the other hand, are designed for low-flow, high-head systems. A common example of an impulse turbine is the Pelton wheel, which looks like a wheel with u-shaped cups lining the outside.  Water hits the cups with high velocity, pushes on the device, and causes it to spin.

Kinetic energy is the main power source in this apparatus, so the velocity of the water plays a bigger role than the flow. The exception to this rule is a water wheel called a crossflow turbine, which maintains functionality in lower head situations. To install an impulse turbine at your home, it is ideal to have 20 ft or more of head.

Since there are so many types of turbines—Pelton, crossflow, Francis, Kaplan, turbo—each designed to produce a different result, talk with a residential hydro company to find out which turbine will be most effective in your micro hydro generation system.  You will also need an expert to design the right pipelines and electrical components to optimize electricity generation for your specific situation.

Cost and Installation

Now that we’ve covered the basics of how a hydro will work at your home, let’s talk about installation.  Total cost for a residential hydroelectric system includes:

• pipes
• turbine
• generator
• inverter
• electronic control system

Cost per kilowatt decreases as the size of the system increases, but it also depends greatly on head available on your property—high head tends to lower total cost.  In a typical home, energy use averaged over a long period of time is around 1kW, but peak demand can easily be ten times that quantity.

For a residential system that generates between 1 and 10kW, total installation cost can vary from $5,000 to $60,000, depending on your head and flow, and the power you would like to generate.  Comparable solar systems will cost about the same per watt, but will produce much less energy since the sun only shines about one-third of the time.  Solar systems also produce more pollution than hydro systems, since the chemicals in a solar cell are energy-intensive to produce and often contain toxic metals.

Unused energy produced by your system can often be sold to the utility, which will help you earn back some of your investment.  Tax credits may be available depending on your location.  Check with your local utility and state government to find out if you have discounts available in your area.

Maximizing Micro Hydro

Today, hydroelectric power is the most widely used renewable energy source.  It accounts for approximately 16% of worldwide electricity production, far outweighing the contributions of solar, wind, and geothermal combined.  Its operation requires no fossil fuels and produces zero global warming gases, though some may be involved in the construction process.

If we were to tap into the full potential of hydro energy, we could greatly increase the renewable section of our energy portfolio.  We could accomplish this by building smaller hydro plants, since ideal sites for large commercial plants have already been developed in the U.S.  Currently, changes are slow since smaller electrical plants cost more to build relative to their power output.

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Posted on May 16, 2008

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