Only a handful of companies are involved in consulting on and building micro-hydro schemes. Ellergreen is one of these companies, working in an industry that has matured steadily since the Feed-in Tariff scheme in April 2010 guaranteed a price for generated capacity.
Most of the schemes use ‘run-of-the-river’ (ROR) designs which use water available at any instant, which means there is little or no storage from a dam. The flow of the river is diverted through turbines, which spin the generators before the water is returned to the river downstream. The ROR designs can be defined as high-head or low-head, defining the distance that the water will drop, anything from 2-5 metres is a low-head, high-heads can be hundreds of metres.
The two installations are suited to different locations and require different equipment, although they work on the same energy principles. Low-head installations are normally redundant water mills at river points and have open bypass channels alongside large generators like Kaplan turbines or Archimedes Screws. High-head schemes, in contrast, are located around streams with steep falls.
They use a hidden penstock pipe to transport the water downwards where the pressurised water is fed through a turbine, such as the Pelton wheel. The high-head installations create greater water pressure, meaning that you get a faster rotating turbine, with lower costs as the torque is higher.
There is also a lower environmental impact, with buried pipelines for the water to run through. However there are strict regulations in place so as not to harm local wildlife. Screens are put in place so that fish cannot get into the generating pipe. These turbines will be particularly useful in remote locations, such as north Wales, Scotland or the Lake District, where it is not possible to export electricity economically.