Anyone who has ever seen a large waterfall understands the enormous amount of energy present in rushing water. Harnessing a natural force of this magnitude requires advanced engineering skill and colossal constructions. Modern hydro power plants have dams that may be over one hundred metres high, huge man-made lakes and turbines weighing hundreds of tonnes.
Huge reservoirs store energy
Dams create reservoirs that allow for greater heights of fall and also serve to regulate energy withdrawal. Water is stored and used when electricity demand is the greatest. The water is directed from the reservoir to a lower level through tunnels, passing a turbine on the way. The type of turbine used depends on the size of the power plant, height of fall and other conditions. The Francis and Kaplan turbines are the most common types, used chiefly in hydro power plants with medium heights of fall. Hydro power plants with higher heights of fall (in the Alps and Norway, for example) normally use a Pelton turbine. A generator then converts the mechanical energy generated by the rotating turbine shaft into electrical energy, a transformer increases the voltage and the electricity is transmitted to the grid.
Long useful life and low operating costs
Hydro power plants are expensive to build. But once the plant is in operation, hydro power is extremely inexpensive. The plants are almost entirely automated, no fuel needs to be purchased and maintenance costs are low. In addition, the useful life of a hydro power plant is long. Many of the plants in operation today were built over 50 years ago and their useful life will continue for many years to come. Investment costs are quickly recouped once the plant is in operation.
Hydro – a balancing power
Hydro power plants can be used both to generate baseload power (the amount of electricity that is always needed) and as balancing power (electricity output that can quickly be turned on to meet variations in demand).
A problem with electricity is that it cannot be stored to any great extent. Water, on the other hand, can be. Water reservoirs next to hydro power plants function as large "batteries". Energy can be stored during the times of the year when water inflow is high and electricity demand is low, and the energy can then be used when demand is greatest.
Output can be turned on quickly
An important characteristic of hydro power is that it generates a great deal of electricity as soon as the water is released, and is not dependent on weather, wind or long, complicated start-up processes, a characteristic not shared by many other types of energy. Hydro power generation can be increased, for instance, to cover shortfalls from wind power and other types of energy that cannot be directly controlled, or from nuclear and coal power plants which take longer to get started.