Hydropower - Environmental Impacts of Renewable Energy - page 128

Mean energy perannum at 80% efficiency= mg ×××
=

h 0 . 8

5 000 000 , , × ×× × 1000 10 300 08 .

= 12,000,0000MJ

12,000,000

Rated output (i.e., mean power) = = 0.381 MW

6 006024 ××× 365

So, maximum power out = 5 × 0.381 = 190 MW, and the time at maximum power
assuming the reservoir falls by 10 m is

Area × DepthDensity

Maximum powe

× ××× gh 0.

r

Days =

1000 × 1000 × 10 × 1000 × 300 × 08 .

=

1 900 000 , , ×× 60 60 × 24

= 146 .days

H ydroturbInes
The two main types of hydroturbines are impulse and reaction (EERE, 2008). The
type of hydropower turbine chosen for a project is based on the height of standing
water—referred to as head —and the flow, or volume of water, at the site. Cost, effi-
ciency desired, and how deep the turbine must be set are other deciding factors. A
cutaway view of a hydroturbine, shafting, and generator connection is provided in
Figure 4.5 , and a typical turbine blade is shown in Figure 4.6 . Figure 4.7 s hows the
generator end of installed turbines, Figure 4.8 s hows the Glen Canyon Dam, and
Figure 4.9 s hows the Grand Coulee Dam spillway.

Impulse Turbine
The impulse turbine uses the velocity of the water to move the runner and discharges
to atmospheric pressure. The water stream hits each bucket on the runner. There is
no suction on the down side of the turbine, and water flows out of the bottom of the
turbine housing after hitting the runner. An impulse turbine is generally suitable for
high-head, low-flow applications.

Reaction Turbine
A reaction turbine develops power from the combined action of pressure and mov-
ing water. The runner is placed directly in the water stream flowing over the blades
rather than striking each individually. Reaction turbines are generally used for sites
with lower head and higher flows than compared with impulse turbines.