Hydroelectric generating stations are generally acknowledged to be the cleanest, cheapest and most efficient method of producing electricity on a large scale. They cause no environmental pollution, use renewable energy and have a very high energy conversion rate. These advantages apply equally to micro-hydro installations; and the chief criticism levelled against large hydro plants, that they disrupt the natural environment, does not apply to most small hydro systems.
Then and Now
Water power has a very long history. It is reported that hydroelectricity first provided light in 1878, when Sir William Armstrong illuminated his picture gallery at Cragside, in Northumberland, with electricity generated by a small hydroelectric plant installed on his estate, powered by water from the lakes. Three years later, the streets of Godalming were lit by hydroelectricity generated by two waterwheels at Westbrook Mill. But the use of waterwheels to provide mechanical power to mills predates electricity generation by very many centuries.
Modern micro hydro installations use water turbines or propellers instead of traditional waterwheels. Water from a stream or small river is diverted into a water intake; it then flows into a penstock pipe running to the powerhouse, where the turbine is situated. The water rushes through the turbine and then returns to the stream via the outflow system. Screens are also installed to prevent fish from swimming into the turbine, and to filter out rubbish and debris that could block or damage the turbines.
Modern turbines are highly efficient, typically converting between 70 and 90 per cent of the energy into electricity. The actual amount of electricity generated depends on the rate of flow, which is dependant on how far the water falls to reach the turbine, and is also affected by the volume of water in the stream. Small domestic turbines typically produce around 5 kilowatts. Installations rated up to 100 kilowatts are classed as micro hydro.
The electricity produced can be used as a direct electricity supply to a nearby building, through an inverter; or it can be stored in a battery bank. Alternatively the system can be connected to the National Grid so that unused electricity can be ‘sold’.
Well-sited micro hydro systems are a reliable source of power. Compared with solar power, supply is better matched with demand because water flow tends to be greatest in winter, when electricity consumption is normally higher. In places where the volume of water in the stream is severely reduced in summer, a good solution can be to use a micro hydro installation in conjunction with a solar powered system. The two energy sources complement each other well because it is normally in hot, sunny weather, when solar power is plentiful, that streams begin to run dry; so between them they can maintain a supply of renewable electricity throughout the year.
The Economics of Micro Hydro Installations in the UK
Installation costs will vary from site to site, but can be high. Once installed, very little maintenance is required, and life expectancy is normally around 25 years. If a system is likely to generates sufficient power to supply all household needs, the anticipation of ‘free’ electricity for 25 years could in itself make this an attractive investment. But the most striking attraction of micro hydro, is that it uses a fully renewable and sustainable energy source and makes zero contribution to climate change.
Globally, water power is the most widely used form of renewable energy, and a number of countries – Norway, for instance – use it to produce well over 90 per cent of their electricity. Unfortunately this is never likely be the case in the UK, as there are no sites suitable for large hydroelectric projects. However, there is plenty of scope for more micro hydro installations, and because of their efficiency and the fact they operate continuously, they would reduce consumption of electricity generated by fossil fuels and make a measurable contribution to lowering the country’s CO2 emissions.