Run of River

Generating electricity from the flow of a river without the use of a dam is referred to as run of river. Rather than creating a reservoir of water it relies on a stream or flow such as a river to supply water to drive a turbine.

The type of turbine and attached generator used will depend on the amount of flow available. The flow of the river or stream may also be diverted or channelled so as to create a greater force. If we had a wide but shallow river and put a small turbine in it, very little of the available water would come into contact with the turbine and the amount of power extracted would be small in comparison to what is available. By making the flow of water narrower or creating a channel to concentrate the flow, placing the same size turbine will have a greater force acting on it and therefore extract more of the natural energy.

One way to achieve this where we have a water flow coming down a hill or mountain side is to have a pipe, called the penstock, collecting water at a high level. The water is then channelled down the incline to a lower level where a generating plant is situated. In such a system the water is now controlled and channelled precisely to the turbine. In such a system, a small dam may be constructed at the higher level though rather than a traditional dam sealing the flow, this will take the form of a construction called a weir. A weir will hold water back and raise the level of the river slightly but is designed so that water freely flows over, under or through it (via sluice gates) so as to not greatly affect the overall flow or course. Holding back this head of water will give a greater stability of supply to the generating station lower down the hillside.

Using run of river systems has the two distinct advantages over dams and reservoirs. Firstly, there is little impact on the environment and secondly, the cost is greatly reduced by not having major construction outlay. There is a major disadvantage though and that is with run of river. If water levels fall through drought conditions or water extraction further upstream takes substantial amounts then the supply to our run of river system will suffer.

A run of river system therefore should be looked upon with the premise that it will be part of a green energy system with other systems in place to cover times of low water. This may simply by adding in an electrical storage system such as a bank of batteries designed to store enough power to continue supply over water shortage periods.

Run of river systems are ideal as well for home use. There are plenty of systems available for implementing oneself and most involve no more than siting a sealed unit into the flow of a water source. These systems, like the one illustrated left may produce just a few hundred watts but others may be obtained to supply several Kw's.