Hydroelectricity is electricity obtained from hydropower. Most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator, although less common variations use water's kinetic energy or dammed sources, such as tidal power. Hydroelectricity is a renewable energy source.
The production of energy via hydrology is perhaps the oldest form of harnessing renewable energy. Water wheels were used several thousand years ago and the method progressed substantially with the advent of the Industrial Revolution. In simple terms, the movement of water into kinetic energy creates modern hydroelectric power.
To produce hydroelectric power it is necessary to utilise the movement of significant amounts of water. Therefore, one would need to utilise a stream or weir. This requirement can prove problematic for many people, however, providing there is a hydro source relatively close by, it would be possible to set up a community hydro project.
Hydro systems can be either connected to the main electricity grid, or off-grid entirely. If the system is on-grid, the excess energy produced can be sold back to energy companies with the potential that you could have a negative electricity bill! An off-grid system would require a battery bank and inverter or you could provide the power direct to the appliances that required it.
A typical hydro system would require a weir to divert the water flow as appropriate, a penstock pipe to pass the water to the turbine, a "powerhouse" (to convert the kinetic energy of the water into electricity), an outflow to release the water back to source and power cabling to deliver the electricity to the necessary points.
There is a small visual impact and the turbines produce some noise, however, these can be avoided by careful planning. The most important environmental aspect to note is that the ecology of the source of water is not negatively disturbed by water flow through the turbine.