Determining the Renewable Energy Source for You

Assessing Microhydro Power Potential At Your Location

While only about 5% of the population in North America has access to suitable streams or rivers, micro hydro electric power is one of the least expensive ways to generate electricity for your home with renewable energy.

It is estimated that only 5% of the population in North America is fortunate enough to have a location suitable for generating microhydro electric power. To take advantage of this form of renewable energy, you need a river or stream that provides sufficient water flow rate and head. Head is the vertical distance between where you would divert the water to your turbine and where it would re-emerge to be joined back with the original water source. You can have heads as low as 6 feet (2 meters) but you will need to have relatively high flow rates to generate any significant power.

To estimate the amount of instantaneous power (watts) you could generate from your location multiply the head (in feet) by the flow rate (in US gallons per minute) and then divde by ten:

• Equation for estimating power for micro hydro: Head (feet) x Flow (US gpm) / 10 = Output (Watts)

For example, let's say you had a site which had a head of 60 feet and 100 gallons per minute. Your instantaneous power available would be 60 x 100 / 10 = 600 Watts. This may not sound like a lot of power, however, remember that in most cases the river is flowing all day and all night long. As a result, to estimate the total daily energy being produced you would multiply the 600 watts times 24 hours, which equals 14,400 watt-hours. Over the period of a month (~30 days) that would be 432,000 watt-hours (or 432 kilowatt-hours). This particular scenario would provide enough electricity to power most energy efficient homes.

Determing flow rate of a stream or a river is usually more challenging than determining the head. One method for determining the flow rate is to see how quickly the stream fills up a bucket of a known volume (e.g. a 5 gallon bucket). For instance, if a five gallon bucket can be filled up in 10 seconds, then you know that over a period of a minute (60 seconds) there would be 35 gallons (5 gallons x 6 re-fills of the bucket in a minute), or 35 gallons per minute (gpm). This method is somewhat challenging as you sometimes need to dam up and divert the stream entirely through a single tube that outputs into your bucket of known quantity.

Another method for estimating the flow rate of a river or stream is to figure out how how fast the water is travel through a particular cross-section. To do this you need to find a length of the stream which is relatively consistent in its width and depth. Measure what those cross-sectional dimensions are (width and depth). Then at the beginning of that known stretch of the stream drop in a floating object such as a ball or stick and time how long it takes to float to the other end of that known stretch. With this information you can estimate the total float rate. For details on exactly how to do this, see our How-To article on Determining the Flow of Your Stream with Simple Float.