There are many types of turbines used for hydropower, and
they are chosen based on their particular application and the height of
standing water—referred to as "head"—available to drive
them. The turning part of the turbine is called the runner. The most
common turbines are as follows:
A Pelton turbine has one or more jets of water impinging on the buckets of
a runner that looks like a water wheel. The Pelton turbines are used for
high-head sites (50 feet to 6,000 feet) and can be as large as 200
A Francis turbine has a runner with fixed vanes, usually nine or more. The
water enters the turbine in a radial direction with respect to the shaft,
and is discharged in an axial direction. Francis turbines will operate
from 10 feet to 2,000 feet of head and can be as large as 800 megawatts.
A propeller has a runner with three to six fixed blades, like a boat
propeller. The water passes through the runner and drives the blades.
Propeller turbines can operate from 10 feet to 300 feet of head and can be
as large as 100 megawatts. A Kaplan turbine is a type of propeller turbine
in which the pitch of the blades can be changed to improve performance.
Kaplan turbines can be as large as 400 megawatts.