Micro-Hydro Power

 

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Information taken from http://www.energyalternatives.ca/

I have always thought that Micro-Hydro Power (if you have a creek/small river running through your property) offered reasonable payback and is environmentally pretty clean (when you don't create physical dams across your water source!). The information below gives some background and technical information. Check out the www.energyalternatives.ca site for information on purchasing equipment.


If your site has a source of running water, you simply must investigate its potential as a source of electricity.

Our experience with micro hydro systems has demonstrated that water power will produce between 10 and 100 times more power than PV or wind for the same capital investment. One should not consider other options unless there is simply no stream available within two kilometers.

Since water flows day and night, a micro hydro system requires far less battery storage than other technologies. Even if the stream is far away, it may still be viable.

Seasonal streams offer great performance when a hybrid water and solar system is designed. When your power requirements are the highest, in the winter, the water is usually flowing the fastest. Solar modules are most efficient when there is the most sun in the summer.

Electricity is produced from the energy in water flowing from a high level to a lower level. This change in elevation is called head and supplies the pressure, which drives the turbine. Flow is the other factor contributing to power production. It is usually limited by the size of the creek.

The amount of electricity produced is directly related to the head and flow. If the head or flow is increased the power output increases proportionally. Many micro hydro systems can utilize the existing pipe used by a gravity fed water system. A couple of sprinklers on a two-inch pipe are the equivalent of many kilowatt-hours per month of micro hydro electricity. Site considerations Many factors work together to make a successful micro hydro site.

In order to have optimal performance your equipment must neither be too big nor too small. A turbine can be up to a couple of kilometers away from where the power is being used and still be cost effective. It is far cheaper to run wire lines than it is to extend the pipe length.

Properly sized transmission lines and high voltage generators can deliver significant amounts of power a long ways away with acceptable losses and in a cost effective fashion.

A large inverter will deliver remarkable service from a small battery based system and save a lot of plumbing and water handling. On the other hand merely going a little higher up the mountain or using larger pipes can produce enough extra power to provide space heating and eliminate batteries altogether by generating AC directly.

If your site permits, you can have a large AC turbine with all the functionality of a 120/240 VAC fossil-fuel generator running 24 hours per day, but without the noise, smell, pollution and ongoing fuel and maintenance costs. While more expensive than a battery charging system, continuous outputs of 3 kW or more will heat a home for much of the year, in addition to supplying town-lifestyle appliance and lighting loads.

There is a lot more at stake, financially and otherwise in higher-powered systems. Please contact us for a reference to an AC micro hydro design professional.

Hydro systems are very site specific. If you are calling us to get a quote for your potential system, please have the head and flow information (next section) ready.

Measuring pressure
Water pressure is what produces power and must be measured carefully. Micro hydro sites range from a few pounds of pressure up to 150 PSI or more. The easiest way to measure pressure is to look at a pressure gauge located at the lowest point of an existing pipeline. When no water is moving in the pipe (static pressure) you can determine the vertical head by multiplying the pressure by 2.31.

If there is no pressure gauge or pipe available, survey the site the old fashioned way. A rod is a stick that is eight feet long with each foot marked. Hold it straight up in the air at the starting point. Every place that is level with the top of the ruler is also eight feet higher than the base. Using a level, sight along to a point that is level with the top of the rod. This is also eight feet above the starting point.

Next move the rod so that you can place the bottom on the piece of ground that you marked as even with the top before. Now, every place that is level with the top of the second setting of the staff is 16 feet higher than the starting point. Repeat as necessary. Heavy brush means setting up more often. Add up your totals to get the elevation in feet.

For high head sites, over 200 feet, a sensitive altimeter can be used. Record the elevation at the bottom. Move to the top, and record the altitude again. The difference in feet is your gross head. Repeat the process and average the results for better accuracy. Because altimeters measure the difference in atmospheric pressure, choose a day when the weather is not changing rapidly. Many modern GPS receivers also offer an altimeter. The reliability of this will depend on your GPS unit and the signal strength. Again, take several readings and average them for best accuracy.

Measuring flow
Flow is the volume of water per unit of time available to the turbine. It varies seasonally and may vary along a creeks length if tributaries flow into it. Measuring the flow at different times of the year helps estimate the maximum and minimum usable flow. Most micro hydro systems use less than a hundred gallons per minute. These flows can be measured by timing how long it takes to fill a bucket. A hundred gallons per minute will take three seconds to fill a five-gallon bucket.

A micro hydro system typically only uses a small portion of the streams flow and has a very minor impact to the overall stream. Diverting too much of the water from a stream will cause a negative environmental impact and should be avoided.

Usually the pipe is the limiting factor in determining what flow is available. Youíd be surprised how small a stream of water even 50 gallons per minute is.

Measuring distance
Some micro hydro systems use pipe that is already installed for other purposes such as irrigation or domestic water supply. 40 PSI is a common household pressure and can easily generate quite a lot of power. But in order to predict how much power a pipe can produce, we need to know how long it is, what kind it is, and what its diameter is. Since power can be moved quite a ways, the distance from where the power is to be generated to where it is to be used needs to be known as well.

Generators
Micro hydro uses a variety of generators to suit the wide range of sites available. A specially adapted automotive alternator provides low cost, DC output. These units are less expensive, but do require more frequent maintenance. Replacing brushes is a relatively inexpensive and simple procedure that may be required every six months to two years of continuous use. A newer, high efficiency permanent magnet brushless generator is also available, which makes this maintenance unnecessary. These units have only one moving part and sealed bearings. Generator maintenance is only required at intervals of many years. These units are adjustable to produce power efficiently over a wide range of pressures.

How much is enough?
There are many answers to this question. No system is large enough to support waste. It is important that you closely examine demand-side management and conservation first, as you would with any alternative energy system.

In a regular house with cheap electrical rates, a household might use 700 kW/h month for basic electrical service, not including heating and cooking which can come from other sources.

Basic energy conservation practices like using compact fluorescent bulbs and the elimination of phantom loads can easily cut this total in half to 350 kW/h per month. Custom appliances, such as energy efficient refrigeration can again reduce this load considerably. You must remember that it is more economical to reduce your power consumption in the first place.

Battery charging systems generally donít provide sufficient power for heating loads, other than intermittent use. It can, however provide a home with the dozens of kilowatt-hours per month it needs for lights and music, or the few hundred kilowatt hours per month necessary for refrigeration and freezing.

Sizing your system
The samples below and formulas on the following page are intended to give you a very rough idea of the capabilities of your potential site. This is by no means a comprehensive system design document, which is beyond the scope of this publication. If you are interested in learning more about detailed design and installation of micro hydro systems, please see our course listings on the following page.

You can determine how much power a system will produce quite accurately when you take all the different factors into account. Exact site measurements are absolutely essential. Simply guessing your head and flow will generally leave you with disappointing results. The samples sites below are intended to give you a very rough idea of the amount of electricity available from various sites. The following page provides some formulas so that you may further calculate your siteís potential. Again, this is only intended as a rough idea. Actual site calculations involve other variables that need to be taken into account.

  • Sample Site 1 - 50 Feet Head
    In this example, we have a site that has 50 feet of gross head or 22 PSI static pressure (pressure with the valve closed). The length of the pipe required to achieve this is 600 feet of two-inch poly pipe. Ordinary irrigation sprinklers will not operate very well in this site, but can produce around 80 kW/h of power per month. This is ample power for efficient lighting, electronics, and modest refrigeration needs.
  • Sample Site 2 - 100 Feet Head
    This sample site is similar to the first example, except it has 100 feet of gross head or 43 PSI static pressure. The same 600 foot length of two-inch pipe is used. This penstock will use 50 GPM. This site can produce over 235 kW/h per month. As you can see, increasing the head has a dramatic effect on the power output. A site such as this is capable of running larger loads such as power tools and larger appliances.
  • Sample Site 3 - Long Pipe
    Letís say that you have a very gradual slope, and will require 6000 feet of two-inch pipe to achieve 100 feet of vertical head. This penstock will use 16 gallons per minute to produce 85 kW/h per month. Although you will spend more time and money on the penstock, this will still be far more economical than Solar, Wind and of course, fossil-fuel generators.
  • Sample Site 4 - Spring Water
    This source of this water is a spring. Spring water is generally warmer than other sources, and is less likely to freeze. A spring that produces 5 GPM, dropping 200 feet in 1.5 inch pipe that is 1000 feet long will produce 70 kW/h per month!
  • Site 5 - High Flow, Low Head
    This site uses 300 feet of four-inch Aluminum or poly pipe with 20 feet of head. If 200 GPM of water is available, it will produce upwards of 185 kW/h per month.
  • Sample Site 6 - Large Site
    A lot of power can be produced by four inch pipe. A 900 foot length of pipe with 310 feet of head that uses ??? GPM can easily produce thousands of kW/h per month. This is enough power to run an energy efficient village or small factory.

Equations

1 cubic ft / sec = 450 USGM = 28.3 liters/sec
1 psi = 2.31 feet of head = 0.7 meters of head


A good approximation of the Power available to a battery charging micro hydro system is given by:

Power = [Watts]
Net Head [ft] x
Flow [USGM]


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Hydro turbines & generators for AC only micro hydro systems are more efficient, so the above power equation needs to be modified:

Power = [Watts]
Net Head [ft] x
Flow [USGM]


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Example Battery System
The total distance between where we wish to draw the water from the creek and where the turbine will be located is 600 feet. Thus the length of the pipeline (LP) must be 600 feet long. Along this 600 foot pipeline there is a drop in elevation of 80 feet. Thus the static head (HS) is 80 feet. The flow (F) available from the creek is measured to be 48 US Gallons per minute.

Lp
= Length of pipeline = 600 feet
Hs
= Static Head = 80 feet
F
= Flow = 48 USGM

From the Pipe Friction Table, friction losses for 2 inch PVC pipe at 48 USGM are 2.7 feet per hundred feet.

Hf
= Friction head = 2.7 feet/100 feet x 600 feet
= 16 feet
Hn
= Net Head = HS - Hf = 80 feet - 16 feet
= 64 feet

Total Power =

64 feet x
48 USGM

= 219 watts
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Power generated would be approximately 219 watts. Over 24 hours just over 5 kWh of energy would be produced.

In a nominal 12 volt system the turbine and generator would deliver approximately 15 amps continuously or 360 amp-hours per day.

 

Copyright 2001-2003  Peter Ferlow