108: Hydro Power Generators

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Interview with Sara F. Hathaway, Book “Day after Disaster”

Sara F. Hathaway day after disaster


Episode 13

Why are hydroelectric generators so highly recommended?

  • Micro-hydro is one of the most efficient forms of electrical power generation.
  • Lowest Cost per Watt of any other power generation.
  • It is fairly easy to predict what your output would be year round, which can result in smaller battery sizes.

They do have some problems:

  • It only provides power with good flow with a decent amount of head pressure, which means it will cause problems for low flow or low elevation locations.
  • Often I have seen that the spring or river needed is a long distance from the home it is meant to power.  This gets extremely expensive with wiring because copper is so expensive
  • They are mechanical in nature, so they do break after a while.

What are the basic mechanics of hydroelectric generators?

hydroelectricity generators

Water is used and directed into blades called a turbine.

The turbine spins and is connected to a shaft which spins a motor, sometimes direct coupled and sometimes using belts for converting low speed high torque inputs to high speed low torque outputs to the motor.

How is the power converted from the generator to a useable current?

The generator, if bought is usually a DC alternator generator.  This is just an AC generator with a one way switch on each phase.

If built, the generator is usually AC, but then sent to a rectifier to convert it to DC.

The DC is then usable by an inverter/charger which decides to either convert the DC to AC to be used, or to dump it to a battery bank for storage.  This same device can convert the stored  capacity to AC to be used when generation is down.

Sometimes the controller will have to dump excess to a resister element.  There are actually hot water heater elements that were designed to convert this wasted energy to heat such as the 600 Watt 12 Volt DC Submersible Water Heater Element that I found on amazon, you can actually use an ac heater element, but as you drop voltage on those elements, you almost reduce the wattage rating by 25%!

There are other ways to use a basic charge controller and consumer grade inverter as well.  It would be a little cheaper if you knew what to look for, but it can be a little more complex.

What would be an easy way to create this system in a long term survival situration with only the materials you could scavenge?

I have seen things built in buckets, using CDs and styrophone, and even articulated PVC devices, but I don’t think most of these are feasible for the type of systems I would build.

Probably the best build would not be what you would call “easy.”

One of the best builds would be a large waterwheel with a gear-ratio change driven by belts or handmade gears.

The awesome thing about waterwheels is that you can couple them up to an alternator or even a mill for grinding grain.

The same wheel could be used to drive a pump that will pump water a long distance… at low flow rates.

If you were wanting something you could use until that was built, you could probably modify a bicycle to run an alternator, with a battery bank, and be very careful how you use your power.

In our current world, if you wanted to reduce your electric bills by using hydro-electric power, what type of system would you build?

The very first thing I would do it to make my home more efficient first.  Biggest bang for your buck.

Then I would look at what my situation is.  

  • Water flow
    • spring, river, waterfall.
  • Is it year round or seasonal
  • How far am I from the source?

At this point, I would probably buy one for the correct purpose.


  • For High flow applications I may go with a permanent magnet alternator
  • For low flow applications I may go with a basic automobile alternator, requires less breakover force




  • Typically for micro-hydro because it is easier to work on
  • Can deal with sand and debris better



  • Designed for efficiency (165 degree angle into buckets, any more will have deflected water interference)
  • It is usually for higher head applications “above 20m” for micro-applications



  • These turbines are much more difficult to make
  • Run much faster, which allows direct coupling (efficiency)
  • Works in a wide range of speeds


  • This is a good one for hand building and is very easy to maintain.
  • Has a low power output
  • A waterwheel with a vertical axis that came out of Napal.

Cross flow

crossflow turbine

  • Squirrel Cage design, like a hamster wheel with blades
  • Resembles the waterwheel with curved blades

Centrifugal Pumps (reverse pump turbines)

centrifugal pump

  • Run water backward through them and they can be found anywhere.
  • They have poor part-flow efficiency, and poor performance
  • Others would be the Francis Turbine, Propeller Turbine

In my book the occupants of this camp turn their hydroelectric generator into a bomb.  Is this concept possible?

I would have to say that it really depends.

  • Is it possible… you can turn almost ANYTHING into a bomb of sorts
  • I don’t think that is is a likely candidate for a bomb
    • The walls of the housing are too thin in something that people will generally get their hands on
    • Most of them have too many gaps and spaces for cooling (not air tight)
  • If you can get a submersible duty housing, you would be able to
    • Then you would have to use something with the force to blow the shell apart
    • If you are resourceful enough to get this type of explosives, you would probably be able to get the fully assembled device.
  • Why would you do this? It would be easier to get and develop something in section of pipe with caps.
  • Much Easier to do with the generator:
    • A more likely scenario would be harnessing the generated power and store it at high voltage to shock someone, but
  • Big explosion? Just disable the pressure relief valve on an electric hot water heater and run it (with plugs that can be disconnected) until it blows… and it would.

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Ken is addicted to fitness and mountain biking. He is such a thrill seeker, people are starting to be concerned!He enjoys MTBing, Hiking, Climbing, Geocaching, Orienteering, Weight Lifting, and Wilderness Survival.

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