1. Energy, Power, and Climate Change 8.6 Hydroelectric Power
We can divide hydroelectric power production into two groups: sun-derived (gravitational energy), and moon-derived (tidal energy).
THE HYDROELECTRIC DAM
The traditional hydroelectric dam uses water at a high potential energy to drive a turbine as the water descends under the gravitational pull to a lower level:
© 2006 By Timothy K. Lund

2. Energy, Power, and Climate Change 8.6 Hydroelectric Power
We can divide hydroelectric power production into two groups: sun-derived (gravitational energy), and moon-derived (tidal energy).
THE HYDROELECTRIC DAM
Calculate the energy yield for the water shown in the reservoir below:
Since each m3 of water has a mass of 1000 kg, we have the total mass of water in the reservoir given by
© 2006 By Timothy K. Lund
m = 1000(1000)(2000)(25)
m = 51010 kg
Since each kilogram of water drops an average of ( )/2 = 87.5 meters, the total potential energy relinquished is given by
U = mgh
= (51010)(10)(87.5)
= 4.381013 J

3. Energy, Power, and Climate Change 8.6 Hydroelectric Power
We can divide hydroelectric power production into two groups: sun-derived (gravitational energy), and moon-derived (tidal energy).
THE HYDROELECTRIC DAM
If the water flow rate is 10 m3 per second, what is the power provided by the moving water?
Since each m3 of water has a mass of 1000 kg, we have the total mass of water each second given by
© 2006 By Timothy K. Lund
m = 1000(10)
m = kg/s
Since each kilogram of water drops an average of ( )/2 = 87.5 meters, the total energy per second is given by
U = mgh
= (10000)(10)(87.5)
= 8.75106 J
FYI: Since 1 J / s is a watt, the power provided by the water is 8.75 MW.

4. Energy, Power, and Climate Change 8.6 Hydroelectric Power
FYI: At night, when power demand is at its lowest, power plants can keep running and use excess power to pump water into a dam's reservoir. This has the effect of storing energy for future use. This is called the PUMPED STORAGE SCHEME.
Energy, Power, and Climate Change 8.6 Hydroelectric Power
We can divide hydroelectric power production into two groups: sun-derived (gravitational energy), and moon-derived (tidal energy).
THE HYDROELECTRIC DAM
If the water flow rate is 10 m3 per second and the reservoir is NOT replenished, how long will it provide power?
The total volume of water in the reservoir is given by
V = 1000(2000)(25)
© 2006 By Timothy K. Lund
V = 5107 m3
5107 m3
1 s
10 m3
= 5106 s
1 h
3600 s
1 d
24 h
= 579 d
FYI: Unlike nuclear and coal power plants, hydroelectric plants can be turned off and on just by controlling the water flow.

5. The Hoover Dam in Colorado can generate 1.5109 watts.
© 2006 By Timothy K. Lund

6. Energy, Power, and Climate Change 8.6 Hydroelectric Power
We can divide hydroelectric power production into two groups: sun-derived (gravitational energy), and moon-derived (tidal energy).
THE TIDAL BARRAGE
In some rivers and on some coastlines, the tidal range (the difference between high and low tide) can be up to 10 to 15 meters.
A dam, called a barrage, is built across the bay, or river, and takes advantage of a two-way turbine scheme: Once when the dammed water is rising, and once when it is falling.
© 2006 By Timothy K. Lund

7. The tidal barrage in Rance, France.
After the tide has brought water into the estuary it is held back and slowly released through 24 turbines producing 240 MW.
The tidal range is up to 13.5 meters at his location.
© 2006 By Timothy K. Lund