Overview of Sources of Energy

Most hydro-power plants run off of the mechanical power available from water, whether the source be from rivers, tides, waves, etc.  The oldest and most widespread source of hydro power is from flowing rivers by either damming the river to use potential energy or letting the river run through the plant to capture kinetic energy.  Although mainly still in development, some methods have been implemented to obtain energy from ocean water mainly from tides and waves.

Conventional Damming

Dammed rivers the most widespread source of hydro-power with the largest plant in the world generating over 20,000 MW.  The way that power is obtained from a dam is very simple, a dam is constructed that obstructs the path of a river to form a reservoir of water behind it.  Water behind the dam is then allowed to flow through a pen-stock, an opening in the dam, to a turbine.  The turbine then converts the energy from the flowing water to power the generator in order to obtain electrical power.  In this manner, the dam converts the potential energy of the water behind the dam into a final product of electrical energy.

In some instances, the water behind the dam is actually pumped there from another another lower elevation reservoir.  This method is known as pumped storage and actually consumes a net amount of energy instead of producing it.  However, economically this a feasible option for companies that generate power as the water is pumped during times of low energy consumption when energy is at a lower cost. Then the dam is then turned on during times of high consumption and when energy costs are higher to support other power plants and obtain a profit for the company.

The power available from a conventional dam is extraordinarily easy to calculate and understand and relies off of the basic equations for mass flow.

$P=ρ*Q*g*h*ɳ$
(Taken from Basic Thermodynamics by Cengel and Boles)

Where ρ is the density of the river, Q is the flow of the river in volume per second, g is the gravitational constant, h is the difference between the inlet and the turbine in term of elevation, and $P=ρ*Q*g*h*ɳ$ is the efficiency of the turbine and generator at converting the energy.