The forces of flowing water have been used in a variety of ways for centuries, and were an important factor in the industrialisation process. Other uses of the potentials of small hydropower are not so widely known.
In the past, pressure reduction valves or shafts were frequently used for this purpose. These reduce not only the pressure, but also the potential energy of the water, and convert it into useless heat. However, the energy can just as easily be converted into electricity with the aid of a turbine. Many water supply companies have gradients in their supply pipelines and distribution networks that are sufficient for the production of electricity. Drinking water power plants are an attractive option since they permit optimal utilisation of the available resources and can be constructed at relatively little extra cost.
There are almost 900 sewage treatment plants currently in operation in Switzerland, and these are capable of treating around 5 million cubic metres of water per day. Some of them are fed with water from agglomerations at a higher altitude with the aid of pressure pipes.
In both sewage treatment plants that are located within the agglomeration itself, as well as lower-lying facilities, it is often the case that a gradient exists before or after the plant that can be used for electricity production.
There are two main principles here:
Weir power plants can to some extent be regarded as power plants within power plants. They are usually integrated into the weirs of hydropower plants and utilise the legally required quantity of residual water to produce electricity with the aid of a turbine.