EPS219 – Energy and the Environment

Homework#11 – Due by email, Thursday, April 30, 2015

1) (10 pts) In the article http://www.nytimes.com/2015/04/12/science/drinking-seawater-looks-ever-more-palatable-to-californians.html#, it talks about how a great deal of energy is used to desalinate water in the desalination plants in California. One way to desalinate water is to boil it, but that is not how these plants operate. What the method here for desalination, and how does it work?

“The technological approach being employed here, and in most recent plants, is called reverse osmosis. It involves forcing seawater through a membrane with holes so tiny that the water molecules can pass through but larger salt molecules cannot.”

2) (10 pts) In the article http://www.nytimes.com/2015/04/23/business/energy-environment/catching-waves-and-turning-them-into-electricity.html, there are two different designs by the Ceto technology company of using buoys to generate electricity and desalinate water. Explain the difference between the two different models.

One model has buoys a couple miles from shore. The up-and-down motion of the buoys pumps water through pipes that head back to shore where the pressure of the water runs electricity turbines and pushes water through the reverse osmosis membranes. The other technology has larger buoys farther out from shore, where the electricity is generated within the buoys, which then gets carried back to shore through electric cables, and the electricity can be used to run the desalination pumps.

3) (10 pts) As explained on Tuesday’s Skyped presentation from Steve Tsu (the powerpoint is on Blackboard), the U.S. solar power industry might undergo a setback following the year 2016. Explain why.

The solar ITC (Investment Tax Credit) of 30% drops to 10% after Dec. 31, 2016, making the purchasing of commercial and residential solar power less financially attractive after that point.

4) (10 pts) Explain how a rate structure for buying electricity (different rates as a function of time of day and time of year) makes rooftop solar more financially attractive than a flat rate.

The most expensive time to buy electricity is during peak usage times, which is during the day and during the summer (when air conditioners are most needed), but these are the times when solar power is most efficient. As a result, if you have solar panels, you don’t need to purchase as much electricity at peak times, or if you sell it back to the grid, you sell it at the highest rates.

5) (20 points) Do you personally think that power from nuclear fission should be an important part public electricity generation over the next century? In justifying your argument, you should include the topics of climate, safety, and nuclear waste.

Answers will vary. Full credit if their answer touches upon the issues of climate, safety, and waste.

6) (20 points) Do you personally feel that Washington University faculty should spend the time and resources carrying out research on ways to lessen the impacts of using coal for electricity generation (such as research on capturing and sequestering carbon)? Explain/justify your answer.

Answers will vary. Full credit if they give a reasonable explanation.

7) (20 points) How far should we go now to making our energy use sustainable for the future? Or, put another way, how far out into the future (a year? a decade? a century? a millennium? indefinitely?) should we be planning for. Where are you on a scale of 1 to 10? (1 = we should do everything possible now to stop pollution from energy consumption, reduce the release of greenhouse gases, enact severe energy conservation practices, and reduce impacts on the biosphere and other environmental systems as much as possible, even if the economic cost is severe; 10 = we do not worry about the impacts of energy consumption on environmental systems, we do not plan for running out of fossil fuels, we choose actions that are the least expensive today (even if there might be long-term costs and consequences for future generations), we let today’s market forces determine our actions). Explain why you chose the number you did.

Answers will vary. Full credit if they give a reasonable explanation.