Small Hydropower & Micro Hydropower

Q: What Causes Hydrostatic Head or Hydraulic Water Pressure?
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Q: How do you Measure Hydrostatic Head for
Small & Micro Hydropower System Site Evaluations?

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A:  Hydrostatic Head – is the pressure rise caused by gravity acting on a column of water or fluid that is not in motion. In the case of a small or micro hydropower system it comes from the difference in elevation between the intake of the hydro system penstock and downhill to the input side of the water turbine.

Figure 1 Hydrostatic Head Measure using a Surveyors Transit or Straight Board & Levels – Method 1 of 3 see page link for more details on all 3 methods.

Link to Details on all 3 Methods for Measuring Hydrostatic Head for your site.

Hydraulic Head in Height Difference or Pressure

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Head can be given as either the difference in elevation or vertical height (Head is a measured height in feet or meters) or it can be expressed as the pressure of the same water column at the turbine inlet (Pressure stated in PSI, KPA, Newtons/m^2, etc.) Either hydraulic head elevation difference or head pressure can be used as it is relatively simple to convert between them as we discuss later.

For Small & Micro Hydropower Systems, Measure Head Accurately!

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The hydro system head measurements will need to be made very accurately since these head measurements play an important role in determination of other hydroelectric system parameters as well.

These head-pressure related system parameters include things such as; hydro turbine selection, system efficiency and fluid dynamic issues. For example; Kaplan, Cross-flow, Francis or Pelton turbines, hydrodynamics of turbine runner blade or bucket design, penstock material and strength, valve types, etc. are all impacted directly by the head measurement. All of these in turn impact the engineering and financial side of the hydro system design.

Because good hydro system design is so dependent on the accuracy of head measurement we will skip the use of mechanical altimeters and GPS units. Typically these have altitude errors on the order of tens of feet or more unless special survey quality GPS instruments are used. As you will see in method 3 below there are instruments that can do the job accurately, repeatedly, with ease and reasonably low cost.

Three accurate hydropower head measurement methods for measuring hydrostatic head are given in the links below, pick one that fits your need or budget and feel free to let us know about any new hydro head measurement methods you have:

The detailed article on the 3 Methods for Measuring Hydrostatic Head for your hydro site is on a different page.  Read the full article page on methods 1 to 3 for more…

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Or you can visit the SmallHydro Info page if you wish to visit that article later.  We’ll be placing a few important reference article links there as we move through the 12 step Small & Micro Hydropower program. The summary follows…

Method 1 – Hydro Head Measure with Surveyors Transit, Levels & Pole

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This method uses a Surveyor’s transit or contractor’s levels and a marked pole. You can use a 20 ft section of PVC pipe marked with a measuring tape attached for easier reading. The transit can be replaced by a straight board and level for economy, watch out for hydro head error buildup with short segments or warped boards or bad leveling though.   For more visit;  Method 1 to 3 details…

Method 2 – Measure Head indirectly with Hose and Pressure gauge

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If the distance is short enough, you can use one or more garden hoses to measure Head.  This method relies on the fact that each vertical foot of Head creates 0.433 psi of water pressure.  For example, 100 vertical feet will generate 43.3 psi in the lower end of your Penstock.  By measuring the pressure in the hose, you can use this conversion factor to calculate the elevation change of your system. We give metric conversions at the bottom of the detailed article too.

Method 3 – Measure Hydro Head with Precision Zip-Level Pro 2000™

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Zip Level Pro 2000 Measure Head

This method is unique to DoradoVista’s approach to hydropower head measurement. We will also show how to use it for accurate flow measurement in a later post about flow measurement methods. It is a very accurate differential pressure based geotechnical instrument. It is extremely accurate when used according to the instructions given by Technidea the manufacturer. This instrument saves time, labor (one person operation is easy) and is the most accurate method we know of for a decent price. 

Read SmallHydro’s Review of the ZipLevel Pro 2000…

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The following diagram depicts DoradoVista’s twelve steps to evaluate a Small or Micro Hydropower site.  As mentioned last month we will be covering each of the twelve evaluation steps in more detail as we update our Small & Micro Hydropower posts.  Again please add comments or questions to each post so that we can address your needs more adequately.

12 Step Small & Micro Hydropower Evaluation Process

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When it comes to hydropower one of the first steps in hydro site evaluation is to perform a site energy survey.  Basically regardless of whether its small or micro hydro the power, a needs survey will help you to tell just how much value there is for the hydro electric energy potential that your site has.

Generally, the Micro Hydro sites will be easier to evaluate since more is known about the site power usage.  A simple checklist of power loads and maximum wattage will suffice to get the initial data.

For Small Hydro sites that plan to export power to the grid, you will need quite a bit more information about grid interconnects and local vs. remote loads, energy price structures and various generation vs. transmission charges associated with commercial power. Frankly this part of project evaluation can be quite intimidating for some energy markets.  Let us know if you need help performing this type of survey and we’ll see what can be done.

Regardless of hydro system size, keep your focus on answering the following question; “What is the market going to pay for this power?”  Later you will need to evaluate “What is the power generation going to cost?”

For a simple appliance load calculation form see ABS Alaskan’s:  Simple Energy Survey Form
Note:  This application does not save data, so fill it and print it out.

One problem with energy surveys is getting a handle on peak power usage. This peak energy need will determine the required maximum hydro generator or battery-inverter capacity. It can be tempting to simply take the sum of all devices and use that for power estimation, don’t do it.  In reality the overall system load capacity will limit out at the maximum rating for the home, farm or cabin’s maximum service panel rating (the big breaker or fuse feeding the whole system.)

Also, it may be worthwhile to count Heating loads as fed by gas or other sources since these can require much larger peak energy loads than is practical.   Hint: Hydropower Load dumps can supply part of this stored heat for a more system savings.

These calculations are designed to compensate for battery inverter conversion losses. Remember your system may have a different conversion efficiency factor. Also remember the hydro turbine and power generator have their efficiency factors as well.

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