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I just watched the June 9, 2023 DW Planet A video In-pipe energy: The hydro power nobody is talking about. It's a "happy story" video light on data and specifics. There's a demonstration for example of charging a cellphone from a backyard spigot at full throttle. (Don't do that at home!)

A fairly constant, reliable and significant pressurization of water mains is important for several reasons. It tries to ensure that if/when there are leaks, bad stuff underground (e.g. nasty microbes, pollutants, dirt) can never get into the water supply.

And of course there is viscous friction and sometimes significant height (potential energy) challenges (which are susceptible to air bubble-induced problems).

So pressure in the mains is a good thing!

And sometimes we depend on the kinetic energy of exiting water to do some work, like washing things.

This leaves me wondering about the following

Question: At which points in a pressurized municipal water distribution system are energy-recovering turbines generally placed as part of "in-pipe energy" generation?

And why is the inevitable pressure drop due to these turbines during flow1 not a problem?


1There is only a pressure drop when the water is actually flowing. The available power is delta-pressure times area (i.e. force) times velocity. The efficiency of the turbine and its distribution system determines what fraction of that power loss you can recover as electrical power.

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  • You might get a better answer on SE Engineering.
    – Fred
    Jul 10, 2023 at 0:56
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    "So pressure in the mains is a good thing!" It is in a well maintained piping network & where taps are also well maintained. In poorly maintained or aged networks, or where someone has a leaky tap, more pressure in the network can lead to a greater amount of leakage water being lost by the system. There's always advantages & disadvantages with everything.
    – Fred
    Jul 10, 2023 at 1:01

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It's an interesting concept. Until now, I didn't know it was being utilized, so I can't state that I know where such in-pipe generators are placed, but I can make some intuitive guesses.

To begin with, such devices will affect flow rates and pressure in the pipes - the energy in the water used to turn the turbines is lost from the water. Additionally due to roughness of the pipe walls and friction, energy will be lost from the water as it moves along the pipe. Also, at all the bends and changes of pipe diameter there will be energy losses. Engineers call them shock losses.

One of the two most likely places where such generators can be placed is at the end of the long slope in a pipeline. This is similar to what happens in hydroelectric power stations. In a municipal system this can be utilized where water is stored in elevated tanks or storage basins. Where such storage systems are located on a hill, place the generators in the pipe at the bottom of the hill.

In flat locations, such as in rural America, towns have water tanks on top of towers. Water is pumped into the tanks and the tanks deliver pressurized water to the town. The pressure in the water leaving the tanks is due to gravity and the height of the tank determines the pressure of the water: P = ρgh, pressure in pascals equals the density of water multiplied by the gravitational constant and the height in meters, P = 9800h, where g is 9.8 m/s2 and ρ is 1000 kg/m3.

If a generator were placed at the bottom of the vertical pipe from the tank and the electricity stored in a battery, the electricity could then be used to power the pumps used to pump the water into the tank. This is similar to pumped hydro electrical energy systems, that a number of large hydroelectric generators use. It enables water to be reused as an energy source.

The other location where I would consider placing an in-pipe generator is just prior to the location of pressure reducing values. Pressure is going to lost anyway, why not assist the pressure reduction process by placing a generator before the pressure reducing value and generate some electricity as a useful by-product.

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