Hydro-electric systems convert potential energy stored in water held at height to kinetic energy to turn a turbine, which in turn produces electricity.
Of course, hydro-electric power is only possible where there is a usable source of running water. Simply having a stream is not enough: you need to either have a sufficient drop in your watercourse to create sufficient water pressure to turn a turbine, or you need to be able to create such a drop by damming a stream.
Hydro-electricity can be one of the cheapest methods of providing renewable energy, but it is also very site specific: you cannot simply order a ‘one size fits all’ system and plug it in, it requires careful planning and adapting to create a system that will work for your location. You require a high flow watercourse with a head of water (i.e. the vertical drop) in order to produce reasonable amounts of energy.
There are lots of variations on hydro-electric systems. For low-cost micro-hydro, using a fast flowing stream or river is the simplest solution. Damming a stream or river to create a reservoir requires a fair amount of engineering and has significant environmental impact. Utilising an existing weir or waterfall can be a simpler solution if you have one. One thing that is important: you need fast flowing water: flat water won’t work. If there is no head to create pressure there is no power.
Hydro-electric systems rely on both head and water flow. A good site has a combination of these two. Systems are generally divided into two categories, low-head and high-head systems.