Homework 6, due fri Nov 13, 2009
			ENVR 30: Fall 2009 

1. Name the four basic types of solar energy devices and give a 2 or 3 sentence
explanation of each.  Rank the four methods in terms of efficient use of solar
energy?  State which method you think will be the most useful eventually and why.

2. Suppose you have a small 1000 square ft. roof, and you cover it with 
photovoltaics.
Use information from the lecture to figure out how many kilowatt hours
you can get per month.  Look at your electricity bill (or someone elses)
and see whether the amount you calculated is more or less than the amount used.
Could you get all your electricity needs met with PV on your roof?
[Hint:  convert area to square meters and multiply by factor in lecture to
get Watts.  Then use efficiency of PV to reduce this.  Then multiply this
available power by time to get energy in one month.]

3. Suppose you have a small 1000 square ft. roof, and you cover it with 
flat plate solar collectors to heat hot water.
Use information from the lecture to how many Btu's of energy you could get per
month.  Use the efficiencies in the lecture to calculate how many gallons of
hot water you could heat from 50 degrees F to 140 degrees F.  Compare this
to the number of gallons of water you estimate you use per month (check water bill).

4. The three Gorges Dam on the Yangste river will be the largest hydroelectric
plant in the world.  
The height of the water will be 80.6 meters and the flow rate will be
about 30000 cubic meters of water per second.  Assume 90% efficiency in
the turbines. (water weighs 1000kg per cubic meter)
a. Calculate how much power it is predicted to produce.
b. How many 1 GW nuclear or coal fired power plants will this replace?
c. The cost is around 30 billion dollars, more than 1 million people had to 
relocate, and it may lead to the "environmental collapse" of the Yangtze river
eco-system.  Look up Three Groges Dam online and answer the question:  
"In your opinion is the three Gorges hydroelectric system worth it"?
Please write your answer in the form of a letter for the editor, backing
up your opinion with facts and giving clear reasons for what you are saying.