EPS219 – Energy and the Environment
Homework#8 – Due in class, Thursday, April 2, 2015
1) (10 pts) Explain why a power utility company might be justified in charging homeowners a monthly “net metering” surcharge if they install rooftop solar panels.
The cost of maintaining the grid of power lines is still the same, and without the surcharge for rooftop-solar users, they would have to charge everyone else a little bit more, and this might adversely affect low-income people who could never afford to install solar panels.
[other answers possible]
2) (10 pts) Explain why a power utility company might not be justified in charging homeowners a monthly “net metering” surcharge if they install rooftop solar panels.
The solar panels would be operating during the day, when power companies have their heaviest load and often have to produce extra electricity at greater costs (such as with gas or natural gas-fired turbines) during the day to meet demands. So, solar panels lessen the utility companies need to produce costly electricity.
3) (10 pts) Explain how the evolution of the way that electric power utilities charge homeowners for electricity has paralleled the history of how individuals have paid for cell-phone usage.
For both, there used to a flat rate for usage. Now, both have varying plans that offer users different rates at different times.
4) (5 pts) Explain the difference between the “shifting” and “curtailing” options for “Demand Response” programs.
With curtailing, consumers will actually use less electricity. With shifting, consumers still end up using the same amount of electricity, but move some of it to off-peak times.
5) (15 pts) The gradient of the Mississippi River is about 0.37 ft/mile as it passes through New Orleans. Suppose that you dammed the river so that the reservoir extended 3 miles behind a hydroelectric dam. How much power could you theoretically get out of the dam? (Hint: You will need to find on the web what the discharge of the River is.)
Answer: (15 pts) (Can be done two different ways)
(From my powerpoint lecture) Power (kW) = 5.9 x Flow (m3/s) x Head (m)
Head = 0.37 ft/mi x 3 mi = 1.1 ft = 0.34 m
Average Flow = ~ 17,000 m3/s [Answer can vary]
Power = 5.9 x 17,000 x .34 = 34,000 kW = 34 MW [Answer can vary][In this case, the “5.9” accounts for a loss in efficiency]
Or
E = mgh so Power = mgh/s = volume x density x g x h /s =
(17,000 m3/s)(1000 kg/m3)(9.8 m/s2)(0.34m)= 57 MW [This doesn’t take loss of efficiency into effect]
6) (10 pts) Explain why are there two high tides and two low tides each day?
Answer: (10 pts) Because there are two bulges from the tides, one on the front and back of the earth. So, as Earth rotates over a day, a point on Earth will pass through both bulges, so will experience two high tides.
7) (20 pts) Suppose you are a municipal electricity supplier and you need to provide a steady source of power. Explain what the separate concerns are for each of hydroelectric, wind, tidal, and ocean wave energy in terms of providing a steady and continuous power source (i.e., what are the forms and sources of the uncertainties in continuity?)
Answer: (20 pts)
Hydroelectric – mostly quite constant, but the amount of power can change over longer periods of time (months to decades) if the amount of rainfall changes between seasons or over the course of an extended drought.
Wind – Very unpredictable. Can change over many different time scales, from minutes to days. One day it can be very windy, the next, not windy at all.
Tidal – VERY predictable, but the magnitude varies significantly over both daily and monthly cycles. But you know what they will be.
Ocean waves – Like wind, it can change over minutes to days. Some days the wave can be small, sometimes large.
8) (10 pts) Explain why a hydroelectric dam reservoir tends to fill up with silt over time.
Flowing water can carry more sediment when it is flowing than when it is standing still. The water that flows from a river into a dam reservoir is initially carrying sediment, but when the water stops moving, the sediment drops out, and the dam can fill us with silt.
9) (10 pts) Explain how a hydroelectric power plant built in the mountains is likely to be less disruptive to the region than a plant built in a relatively flat region.
In a mountainous area where the sides of the canyon are steep, a relatively small area is flooded to make the dam reservoir. In the flat region, the same vertical height for the dam could result in a very large area that gets flooded, displacing many more people from their homes.