Microhydro Systems: Advice From The Pros: Page 2 of 6

Beginner
Microhydro Intake
The right intake design will affect system performance greatly.
Microhydro Intake Site
Asian Phoenix’s Power Pal Low-Head Turbine
Asian Phoenix’s Power Pal low-head turbine in Honduras. At lower heads than this, things get tricky.
Altimeter
An altimeter is used to survey elevation. This measurement shows only 180 feet of head, but with a 12-inch pipe, this site will develop 75 kW.
Don Harris
Hydro guru Don Harris.
Measuring Head with the Bucket Method
The “bucket method” can be used to measure flow in small streams. Larger streams require an alternative measurement method.
Measuring Head with a Pressure Gauge
95 psi shows the static head of almost 220 feet of head.
Hugh Piggott, Scoraig Wind Electric
Hugh Piggott, Scoraig Wind Electric
David Seymore, Asian Phoenix Resources
David Seymore, Asian Phoenix Resources
Denis Ledbetter, Lo Power Engineering
Denis Ledbetter, Lo Power Engineering
Christopher Freitas, WiFu Energy
Christopher Freitas, WiFu Energy
Joseph Hartvigsen, Hartvigsen-Hydro
Joseph Hartvigsen, Hartvigsen-Hydro
Scott Davis, Friends of Renewable Energy BC
Scott Davis, Friends of Renewable Energy BC
Excavator Placing Pipe
An excavator lifting a 3,000-pound section of 8-inch steel onto a steep slope. The pipe was then pulled 500 feet up the hill using the excavator and a long steel cable through a pulley.
Microhydro Intake
Microhydro Intake Site
Asian Phoenix’s Power Pal Low-Head Turbine
Altimeter
Don Harris
Measuring Head with the Bucket Method
Measuring Head with a Pressure Gauge
Hugh Piggott, Scoraig Wind Electric
David Seymore, Asian Phoenix Resources
Denis Ledbetter, Lo Power Engineering
Christopher Freitas, WiFu Energy
Joseph Hartvigsen, Hartvigsen-Hydro
Scott Davis, Friends of Renewable Energy BC
Excavator Placing Pipe

Obviously, water that is not moving has no energy in it. And water that is being pumped is not a source of renewable energy, since it takes more energy to develop the pressure than can be gotten back from it. Some fish-bearing streams may not be a wise choice for development due to environmental impact. And of course, you need to have legal access to the water source, and the ability to tap it without undue restrictions.

Very high-head sites (above 500 feet) can be costly to tap because of long pipe runs and high pressure. Tapping a part of the available head can be a viable solution. Also note that water sources that have very high water at some time in the year make for difficult intakes. High water often means a lot of debris comes down the stream, which can clog or damage intakes. And some intake designs do not function well if submerged.

Other inappropriate sources would be using drinking or irrigation water systems just to make electricity. These sources often rely on energy to pump and pressurize the water, so they are not actually renewable energy sources. And the intended end uses often need pressure, which a hydro system brings to zero. In addition, the volume of flow is usually not adequate to make much energy. 

Q: Once you’ve identified a potential site, what measurements do you take to assess the site’s production capacity? What are the best methods for taking these measurements?

Several measurements are needed, and there are multiple ways to obtain most of them. Most important is to take very accurate measurements of head and flow. This will tell you how much power is available, and the type of turbine appropriate to the site.

To measure vertical drop (head), you can use:

  • Altimeters, if meter accuracy is good
  • GPS units (some may have enough accuracy)
  • Survey level or laser level
  • Maps with good contour lines, for higher-head sites
  • Google Earth (in some cases) for offsite pre-assessment
  • Accurate pressure gauge (if there is an existing pipeline)

To measure flow (this is best done multiple times throughout the year to ascertain seasonal variations):

  • Bucket and stop watch to measure gallons per minute for small- to medium-flow sources and time surface velocity
  • Weir with measuring notch and appropriate flow tables
  • 100-foot (or longer) tape measure to determine the cross-section of stream 

See “Intro to Hydropower, Part 2: Measuring Head & Flow” in HP104 for more details.

Q: What do you consider to be the maximum feasible distances for penstock length and transmission wire run?

This depends on the scale of the system, the power available, cost of alternatives, the system voltage, and the terrain, among other factors. Penstock and transmission cable lengths of more than a mile are workable in the right situations, though less than 1/2 mile is more typical.

If you need long pipe and long cable, the site will need to be very good or the economics may not work. But if you need a long pipe and a short cable or a short pipe and a long cable, you may have a viable site. There are too many variables involved to generalize on distance limits, because so much depends upon the diameter and the material composition of the penstock that is required for the local conditions, and the voltage, distance, and size of wire.

Comments (3)

Heetel64's picture

If you are lucky enough to have a water source, study it.
An example would be a water source with a bend. Consider putting two independent wheels, smaller one on the outside ( faster flow ) and larger one on the inside with reducer gearing ( slower flow ). Should you find that the water supply is reduced, then design your system to allow for moving the larger wheel into the outer bend.
Never think that your water source will never change.

Frank Heller's picture

For remote sites where the owner has access to enough water to generate 1+ KW; it may be advisable to install microhydro should the distance to the nearest power line be 2 or more poles away. In Maine, a pole typically costs about $9,000.

On the other hand going off the grid is not for the faint hearted.

Frank Heller's picture

Don't dismiss the water wheel so quickly. A large slowly turning water wheel can provide enough torque to power a transmission so that a 300:1 or greater increase in RPM can be obtained. A large wheel with a small amount of water may do the same. Depends on whether it is in the current or powered by the weight of falling water.

There are also large volumes of water impounded in tidal pounds that can power a modern equivalent of the Roman tub turbine. In Maine we have 11' tides and there is an infrastructure of tidal ponds which ran approx. 2,000 tidal water mills.

OREC and others now use variations of the Gorlov turbine in swift underwater ocean currents. Tidal barrages using compression waves can also drive large turbines, i.e. SEABELL of Tokyo.

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