Estimating Micro Hydro Head

Head is the vertical height difference between the point at which water is taken into a micro hydro system and the point at which it is discharged. On a high head site, this is typically the difference in level between the intake and the turbine location. On a low head site, such as a site with a weir, it is normally the difference between upstream and downstream water levels.

Head is fundamental because it directly affects the energy available within the water. A site with modest flow and good head can be very attractive, while a site with large volumes of water but little usable drop may be less productive than first expected.

At this stage, the aim is not to produce a survey-grade figure. The aim is to develop a sensible early-stage estimate so that the site can be screened properly before moving on to more detailed work.

A practical first step is to use mapping to identify the proposed intake position and the likely turbine location. This approach allows an initial estimate to be made quickly. It is not intended to replace proper site measurements, but it is often enough to determine whether a scheme is likely to justify further attention.

An early estimate of gross head is useful, but the scheme will ultimately depend on net head. Net head is lower once losses through the pipework, fittings and hydraulic arrangement are taken into account.