==Hydroelectric power==

==8.4.15 Distinguish between different hydroelectric schemes.==

Ways to gain gravitational energy:

1.) The water cycle: rain falls and is collected in reservoirs
2.) Tidal power: water is trapped during high tides and released during low tides
3.) Water pumps: water is pumped from a low reservoir to a high reservoir, then the water flows back downhill. Large scale method of storing energy.


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8.4.16 Describe the main energy transformations that take place in hydroelectric schemes.


To get electricity, hydroelectric power plants transform the gravitational potential energy from water moving downhill to "generate electrical energy" (tim kirk)

The water moves down through a penstock to gain kenetic energy from its graviational protential energy from its raised level. The water then transfers its kenetic energy to the kenetic energy of a turbine, which moves a magnet through coils of wire to create electricity.
Power Plant

8.4.17 Solve problems involving hydroelectric schemes. hydro.gif

Using the diagram shown above:

a.) State whether the height of the water will remain constant or will change. Explain in detail how such a system might work to provide electrical energy form tides .

b.)Using the following information, find the energy in kWh produced form the hydro electric scheme:
- maximum water height above turbine= 20.0 m
- the dam is 30.0m wide and the lake is 500. m long
-the density of water is 1000.kgm^-3

ANSWER:

a.) this is a damming hydroelectric scheme, so the water source is a river. A river is a non-dminishing water source so the height will be constant.

b.) Potential Energy = mg∆h
g = 9.81ms^-2
h = 20.0m
Density = Mass / Volume
Mass = Volume x Density
Volume = Area x Depth
Area = Width x Length = 30.0m x 500.0m = 15000m^2
Depth = 20.0m
Volume = Area x Depth = 20.0m x 15000m^2 =300000m^3
Mass= Density x Volume = 1000.kgm^-3 x 300000m^3 = 3.0x10^8kg
Potential Energy = (3.0x10^8kg x 9.81ms^-2 x 20.0m) = 5.90x10^10J
Energy = 5.9x10^10J / 3.6x10^6JkWh^-1 = 16350kWh = 1.64x10^4kWh