5.3: Methods of Harnessing Hydropower

How exactly is electric power generated at hydropower facilities? There are two major techniques. One is by exploiting rivers in which the stream gradient is not very high, but high is the volume of water flowing downriver. Along the river bed, the flowing water gradually loses its potential energy. If there is a dam on the river giving rise to an artificial lake, however, then the potential energy of water flowing into the lake is “fixed” at a value cor- responding to the altitude of the lake’s surface. Now, if there is an opening in the dam at the lake’s bottom, the water squirts out, its potential energy at the surface level is converted to kinetic energy.

The speed of the “jet” flowing out is given by the solution of the famous tank draining problem, formulated by Daniel Bernoulli nearly 300 years ago – and is:

\[v=\sqrt{2 g\left(H_{\text {high }}-H_{\text {low }}\right)} \notag \]

where g is the acceleration due to the Earth’s gravity. For details of the formula derivation, look, e.g., at this Web site.

Figure \(\PageIndex{1}\): Making a dam saves the energy of flowing water – otherwise, the energy is gradually dissipated along the river bed.

• 5.3.1: The Kaplan and Francis Turbines

• 5.3.2: The Pelton Turbine