Microhydro

Microhydro systems are specifically those systems that are not grand in scale. Damming a river usually will not qualify as microhydro, but partially diverting a stream into a holding tank and running the water into a small hydro-electric turbine or pelton wheel is more along the lines of what the term microhydro refers to.

The following article is a brief overview of the more technical aspects and considerations needed to design and construct a microhydro system.

Determining available power

See Hydropower#Analyzing_the_available_hydropower and Hydroelectricity#Determining_the_powerpotential_of_a_site

Choosing an water energy harvester

The water energy harvester you can use greatly depends on the specific flow of the water energy source you have available (for example, does the water come from a hill or does it flow relatively horiontal ?). In addition, it also depends on what your objective is (ie do you want to produce electricity, generate simple mechanical work, store electricity ?), your budget (which determines the size of the device you can build) and the impact on the water source (it is best not to use the full potential energy of the water source so that organisms living in the water source are not disturbed too much).

The flow of the water energy source

Depending on whether the stream runs horizontal, or whether it comes from a hill, more "head" is available, which means that we can use different types of water wheels or hydroelectric turbines. Head is the difference in elevation between the point where you start capturing the water (beginning of stream or water diversion) and where you start the use it (where the hydroelectric system is set up). Systems requiring a high head include: Pelton and Turgo turbine, and backshot and overshot water wheels. Systems that require little head and a high flow are Crossflow turbines and breastshot water wheels. Finally, when there is no head available whatsoever (horizontal stream), a undershot water wheel can be used.^[1]

In order to asses the amount of flow and head available, it is necessairy to measure it. The height elevation can be measured using measuring tap or a height meter. The flow can be measured by building a temporary dam with a pipe. By then filling a container with a known volume while measuring the time required for this with a stopwatch, we know the flow.

Water wheels

Probably the most accessible technology for hydro power is the water wheel^W. It can be built entirely from local materials. Only the generator has to be brought in. For small systems a modified motor or car alternator can be used.

• The vertical undershot water wheel is most appropriate for relative low head situations even if it is the least efficient of all water wheels. You should avoid building an undershot wheel with straight buckets and go for either a Poncelet wheel or a Zuppinger wheel which can both double the efficiency. They have an efficiency of about 30%, but enclosed like a breast shot of up to 70%.

• The breast shot is next when the head is large enough. Here the water enters at a height similar to the axle height. It is more complicated to build and needs a structure that encases the wheel to function with high efficiency. If done correctly it uses the weight of the water and its impulse. It can have an efficiency of about 85% if it's well-built.

• The over shot wheel needs the most head of the water wheels. Under optimal conditions with steel buckets it can have an efficiency of up to 80%.

• The back shot wheel can be seen as an cross between a breast shot wheel and an overshoot wheel. The water enters at the top of the wheel but the buckets are like a breast shot wheel. The direction of rotation is the same as in a breast shot wheel. The efficiency can exceed that of the breast shot.

• Horizontal water wheels apart from museum pieces are today found mainly in the Himalaya region in the form of the ghatta. That version is a primitive version of a turbine.

Impulse turbines

The only machine that can be build without access to metal casting equipment or a 3D milling machine is the crossflow turbine. The only advanced tools needed are a cutting torch and welding equipment. Needed raw materials are sheet metal and metal pipe. Information how to build a crossflow turbine can be found on the CD3WD ( see Resources ) web site.

To build runners for small Pelton or Turgo turbines it is necessary to have either access to a 3D milling machine or have access to a casting shop or to build a casting shop. For the latter the largest problem is probably to get information how to build a mold for a suitable runner. For more information see Casting ( Metal )

Installing a water turbine

When installing a waterwheel, often a alternator or dynamo and a gear reducer or gear increaser is needed (so that the RPM of the alternator is brought to a suitble speed, converting the electrical energy efficiently).

Regardless of the type of water turbine used, the optimal power output is not obtained in practice at rotation speeds of the axle above or below what the water turbine was designed for (for example at times of high water/high flow, ...). This is due to the alternator or dynamo used, which tends to be chosen for a specific speed. If the water speed goes above or below this speed, the efficiency is much lower than what could actually be harvested at this time. This could be solved using a gearbox which may be electrically controlled (changing gear ratio's when needed). However, due to the high complexity, this is often not done and a regular gear reducer or gear increaser is used.

References

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Resources

• http://www.microhydropower.net/
  • Check out their case studies (under the resources pull down window). Avoid their theory sections.

• http://www.homepower.com/basics/hydro/
  • Great basics of microhydro from Home Power magazine.

• http://www.retscreen.net/download.php/ang/109/0/Textbook_Hydro.pdf
  • Awesome textbook on small hydropower installations.
  • They also have data, case studies and tools available for doing project analysis. See http://www.retscreen.net/ang/g_small.php for much more.

• wikipedia:Hydroelectric power and wikipedia:micro hydro
  • More information from wikipedia.

• Micro Hydro
  • A visual directory of microhydro resources from the Renewable Energy Directory.

• DC Micro Hydro Examples and AC Micro Hydro Examples
  • A great resource with pictures, statistics, and an overview of the necessary elements of micro hydro.

• CD3WD - Helping the 3rd World to help itself
  • A website which gathers articles from NGO's and other organizations and compiles them on CD's . The images of that CD's can be downloaded through their website. The CD's that have identified by me to contain information about hydro power are cd3wd407 and cd3wd430.

• Power versus Pipe Diameter
  • Live spreadsheet graph of Power versus Pipe Diameter for Various Flows (0 to 150GPM). Customizable amount of run and fittings.

• Ashden Awards
  • Awesome case studies with videos from Ashden Awards.

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Interwiki links

• Wikipedia:Microhydro