# Hydraulic Head

The hydraulic head is the distance that water flows from the higher elevation where it is stored, to the hydro-turbine generator.

The measurement includes the distance water travels down through the penstock and into the turbine.  It is the distance between where the water begins to descend, and the hydro turbine generator.  The larger the elevation of the hydraulic head, the greater the force of the flowing water.

Hydraulic head is usually divided into three categories: low, medium, and high head.

Elevations above around 100 meters are usually considered high head, while low head system elevations range around 10 meters in height.

There are a few ways to measure the hydraulic head height when deciding a location for a new system. The easiest and most efficient way is to use a GPS system; this will give the exact elevation of the turbine and the elevation of the original water source.  The difference in height is the head height.

You could also use the simple “garden hose” method, where two people hold a garden hose filled with water: one at the original starting point of the water flow, and the other at the location of the turbine.  The person at the location of the turbine will slowly lift the hose until the water stops flowing out, meaning that the hose is at equal elevations at both ends.  Then, by measuring the distance that the hose has been lifted off the ground, you will get the  hydraulic head height.

## High Head Hydro Turbine

A high head hydro turbine is a hydropower system in which the water traveling through the turbine originates from a significantly higher elevation.

A high head hydro turbine system requires less volume of water flow to operate because the momentum collected from gravity through the longer distance of falling water makes up for the loss of volume.

The high head systems also require a smaller turbine because of the lower volume of water flow needed.

The size of the turbine needed in a high head system is what makes the system advantageous.  The smaller turbine required greatly lowers the price of the turbine and generator compared to a high volume, low head system.

A high head hydro turbine is the style of turbine that will most likely be used in a home micro-hydro power system.  Micro-hydro systems have been growing in popularity over the last several years, and have become a great resource for anyone looking to use hydropower electric generation in their home.

## Low Head Hydro Turbine

A low head hydro turbine is usually used in a flowing river with little elevation change, or in moving ocean tides.

A low head system with a high volume of water usually requires a much larger turbine generator to efficiently convert the water energy into electricity.

Building a dam is not always required in a low head system, hydroelectric dams are a very common form of hydroelectric generation today and usually consists of large turbines with a high volume of water.