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Microhydro assessment: Measuring head

The other important measurement to take when assessing your creek for microhydro is pressure or head.  The two terms are different measurements of the same thing --- potential energy just waiting to turn your turbine and make some power.

Many homesteaders pipe water from a spring down to their house, and the energy in the water line can be tapped for microhydro power.  To measure pressure directly in such a situation, install a gressure gauge in the line and read the dial.

If you don't already have a water line in place, you're better off calculating a stream's head rather than measuring pressure directly.  Head is simply the change in elevation between the highest and lowest points of a stream, and it can be measured in several different ways.  If you have a gps or watch with an altimeter, this can give a rough measurement of the respective elevations, but I found the water level method (outlined in the embedded video) to be the simplest.

To measure head using the water level method, find an inflexible length of pipe and start at the stream's highest point.  Completely submerge the pipe, then slowly lift the downhill end out of the water.  Creek water will flow out of the pipe's downhill end until it is raised level with the uphill end, at which point water will stop flowing.  Measure the vertical distance between the downhill end of the pipe and the ground and you have the change in elevation between the two points.  Now scoot the pipe downstream until the uphill end rests where the downhill end used to be, and repeat your measurement.  Lather, rinse, and repeat until you run out of shampoo...er, reach the end of the stream.  The head is the sum of all of the elevations measured along the creek's length.

The downfall of our property's creeks is their valley-bottom flatness.  Our small creek has the largest head, and even there the total change in elevation is barely over three feet.  Granted, microhydro applications can work with as little as 2 feet of head, but the setup becomes much pricier if your head is less than 50 feet.



This post is part of our Microhydro lunchtime series.  Read all of the entries:





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Another easy way is to use a garden hose (or a clear hose is even easier, if you have one). Fill the hose with water. Get someone to hold one end, while you walk around with the other end. The water level at your end will always be the same elevation as the water level at the other end, so it's pretty easy to either mark out contours or measure drops.
Comment by Darren (Green Change) Thu Mar 4 17:27:02 2010
I thought that's what the book was suggesting when I first read it, but I think it'd be hard to use a hose to measure head --- it's just too flexible and would bow in the middle. Or maybe I'm visualizing it wrong?
Comment by anna Thu Mar 4 19:26:59 2010
no but it does not matter if it bows in the midddle. all that matters are the ends. well as long as you dont have kinks.
Comment by Anonymous Thu Mar 4 22:13:14 2010
I was going to suggest the hose also... As long as the upstream end does not come out of the water, you should be able to measure head height/pressure over hundreds of feet of stream length.
Comment by Shannon Thu Mar 4 23:29:33 2010
I guess it would work, as long as your creek was completely flat. It sounds harder than my rigid pipe, though. Imagine draping a hose down through the irregular contours of a creek. If you accidentally let it sit on a rock, the water will stop flowing right there because that's the highest point. But maybe most creeks aren't as bumpy as mine. :-)
Comment by anna Fri Mar 5 07:36:57 2010

One very unique homestead, $1,500 per acre, the opportunity of a lifetime