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Micro Hydro

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 don't 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 site's 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
Let's 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.

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