8.4 Hydroelectric Power

Question 1

What happens is a volume of water delta V with a height h above a chosen horizontal level drops what happens to the gravitational potential energy?

Answer 1

It is converted to kinetic energy as it flows through the pipe at the bottom.

Question 2

How is the mass of the water related to its potential energy?

Answer 2

Mass is m = delta V where p is the density of water so its potential energy is
mgh = pdeltaVgh. The rate P (power) at which this potential energy is converted is therefore
P = p (delta V/delta t) gh

Question 3

If the surface area of the dam is A then what is its volume and how will this affect the rate at which its volume changes?

Answer 3

V = Ah

delta V/delta t = A(delta h/delta t)
so P = pA(delta h/delta t) gh

The power depends on the height of the water and the rate at which the height changes.

Question 4

What are the advantages of hydroelectric energy?

Answer 4

Unlimited energy supply
No extraction costs
Clean

Question 5

What are the disadvantages of hydroelectric energy?

Answer 5

Very location dependent
Dams and reservoirs require serious changes to the environment
High initial costs

Question 6

What is pumped storage?

Answer 6

A way to store hydroelectric energy on a large scale. Water is pumped to a higher reservoir during low demand periods and then flows back down to generate electricity during high demand periods. This many seem silly since pumping it requires energy, more energy than is regained when it is allowed to flow down again. But if the electricity to pump it up comes from other sources at off peak times when energy prices are lower then the net effect is an increase in energy available at peak times but at off peak rates.