Estimating Head

Estimating Head

Head is the vertical height difference between the point at which water is abstracted and where it is discharged.

For a high head site this would be the difference in height between where the pipe starts and the location of the turbine. For a low head site it is the difference in water levels across a weir.

Head that is below 10 meters is considered low, on low head sites a high volume of flow is required to generate electricity. Head that is above 20 meters is considered high, on high head sites less flow is required because gravity adds to the pressure reaching the turbine.

Once you have an estimate of both head and flow you can enter it into our Output Calculator to obtain an outline of the power available at your site.

For low head sites, such as a site with a weir, simply measure the difference in height between the upstream and downstream water levels.

Estimating Head – For a high head site, follow the simple steps below:

In your web browser go to www.streetmap.co.uk and enter your postcode or grid reference (click here for guidance on how to obtain a grid reference) and hit Enter or click ‘Go’.

Estimating Head

Using the Move Arrow button relocate the arrow on the map to be at the top of your proposed pipe, i.e. the intake location of the proposed hydro system. Also use the zoom function to show a 1:25000 scale map.

Estimating Head

On the map below is a red oval to highlight that you should check that the contour lines are in 10 meter intervals. You can see from the map that this example shows the height of 410 meters with the next interval being 400 meters. The map you are looking at should display 10 meter intervals on the contour lines. Also on the below map is the arrow showing the proposed intake. Now you need to mark where the turbine will be, in our below example we have used a red cross (X).

Estimating Head

By simply counting the contour lines between the intake point (arrow) and the turbine location (red X) and multiplying the number by 10 you will have an idea of the height difference between the two points, this is the head.

Calculate Estimating Flow