A New Era in Home-Owner Hydro

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Head is fixed. It won't change in a lifetime. Streamflow is trickier. It's always in flux. Are you measuring during snowmelt? In the dry season? After a big rain?

Since any single measurement of flow is probably unrepresentative, it's best to measure flow repeatedly over the course of a year. What you want to establish is the reliable yield. Try also to establish a winter flow, since that's the season you'll probably use most electricity. This will help you determine how close hydro will come to meeting your energy needs.

There are many ways to measure flow. For a shallow stream, three or four feet wide, the bucket-and-stopwatch method is simplest. Build a temporary dam with stones, dirt, and plastic tarp, leaving an outlet to one side. Next, improvise a trough (a piece of culvert or metal roofing works well) to channel the entire stream into a container of known volume. Time how long it takes to fill. If a five-gallon bucket fills in 15 seconds, the flow is 20 gallons per minute.

As stream size increases, measuring flow becomes more difficult. Unless you contemplate an AC system, it also becomes somewhat less important. Remember, if you've got 50 feet or more head, two gallons a second is all you really need.

The best way to measure stream flow in large streams is to dam them with a wooden weir, with a rectangular opening of known size in its center. (Sometimes easier said than done.) Next, measure the difference in height between the bottom of that opening and the top of the pond that forms a few feet upstream. Plug this measurement into a "flow rate weir table" (found in a hydropower textbook) to get your flow.

Strive to be accurate as you measure head and flow, but don't worry if you're off by a few inches or ounces. Close enough is good enough.

Regulations and Red Tape

After measuring head and flow, and estimating your power output, you decide to build. The first step is to obtain the necessary permits. Here, generalizations really are useless. In some states, small hydro systems aren't regulated. In others, they get lumped in with domestic water systems, which rarely encounter permitting problems. (If you are developing a new homesite, design your penstock to provide both water and power.) Finally, there are states, California for example, where the red tape is more formidable.

In truth, many people fail to get a permit, either as an act of civil disobedience or because they fear bureaucrats who strain at gnats while swallowing camels or because they just don't want to bother. But this can be risky.

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