Last updated 18th March 2002
Obviously not everywhere has flowing water and even where there is, it not provide enough power for practical use. The amount of power that can be provided by a stream depends on to two things. These are called the head and the flow.
The head (measured in metres(m)) is the vertical drop from the top of system (where the water enters your pipe/penstock) to the bottom (where it is released). Head should not be confused with the distance between the top and bottom of the system (which should be kept to a minimum). It is the difference in height, the drop, that counts. The greater the head, the higher the potential power. There are several ways you might measure the head. You could check an ordinance survey map for contour lines. You could measure the straight line distance between top and bottom and the angle between the two and use trigonometry. You could even borrow an altimeter (some gimmicky watches have them).
The flow (measured in litres per second (l/s)), is the volume of water which flows past any given point in the system within the period of one second. It needs to be measured before the turbine is in place in order to find the potential power because the flow will be reduced when it is fitted. The greater the flow, the higher the potential power. There are several ways to measure flow but the simplest is to use a bucket of a known capacity and time how long it takes to fill. Eg. If it take 5 seconds to fill a 10 litre bucket you have 2 litres per second.
Calculating the power (measured in watts (W)), is done by multiplying the head and flow by the force of gravity (around 9.8 m/s/s which you can't easily change significantly without leaving the planet). For ease of calculation you could use 10 m/s/s as the force of gravity - no one will notice (unless they are very unfit).
The main parts of a hydro system are the penstock and the turbine. The penstock is any artificial method by which you get water to your turbine from the highest point in your system with the minimum of obstruction and resistance. Penstock may be in the form of pipes or an artificial channel but sometimes the landscape may have provided a natural solution.
Other factors that effect the amount of power available include the resistance experienced by the water while on its way to your turbine which is directly proportional to the length of your penstock. If you are using pipe it is important to use a large enough diameter and keep it as short as possible while still providing the amount of head you want. Avoid any sharp bends or joins etc.
The type of turbine you use will dictate how much of the available
power you can actually provide to the generator and the efficiency of
the generator will dictate the amount of electrical power provided.
You will probably get less than half the available power. Your losses
don't end there. If your turbine is located a great distance from the
site you plan to use you power you may also have transmission losses
in the cable. But what the hell, even with the losses, something is
better than nothing.
This page will be updated to include;
Keep It Simple Stupid: Don't forget that you don't have to produce electricity when you need power. When it is possible to do so, you will find it more efficient to use the available mechanical power directly. For example; powering machinery such as a saw mill, grinder, stone polisher etc.
For more detailed information on the subject of small scale hydro power you might like to consult these outside links:
Micro Hydro Centre - Research, information and development projects.
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