HYDROELECTRIC ENERGY

For centuries, mankind has used water as its main source of mechanical energy. The first historical registry of such a use of water belongs to Antipater of Thessalonica, who lived in the first century BC. In more recent times, the great hydroelectric dams have been the answer to our society’s increasingly higher requirements for electricity.

In a dam, the potential energy of water in the reservoir is transformed into kinetic energy during the fall. Water drives the turbine/generator which in turn generates electricity. Even a slight difference in the level of water, as in the case of large plain rivers, is enough to generate electricity.

Hydraulic turbines can be generally classified as action runners (e.g. Pelton runners) and reaction runners (e.g. Francis and Kaplan runners). Runners are selected depending on the head of water and the flow.  The efficiency of hydraulic turbines oscillates between 80% and 90%.

Water is also used as a means of storing energy. In a pumped-storage hydroelectric power plant, water is pumped from the lower reservoir to the elevated one during the hours of minimum consumption of electricity (off-peak periods). The process is reversed to generate electricity during the peak-load periods. The efficiency of these plants runs between 60% and 70%.

Two serious drawbacks for the construction of large hydroelectric plants are the need of a huge investment and the fact that they may alter the local climate and environment.  Nevertheless, the benefit of clean electricity generation clearly outweighs these drawbacks. Also, small hydroelectric plants on local waterfalls are a useful solution for places that are far from the national electric grid.

GMF2004