It is impossible to use appropriate run-of-stream turbines to ...

[ahriuashd]

It is impossible to use appropriate run-of-stream turbines to capture tidal energy.
 
  What will be an ideal response?

Question 2

In 1987, the best refrigerator being sold used 515 kWh/yr and the average used 979 kWh/yr. How much money would have been saved on your electric bill between then and 2000 by buying the more efficient one?
 
  What will be an ideal response?

[zhanghao]

Answer to Question 1

There are relatively inexpensive models sold by Chinese companies. Also, new
technologies such as the Davis and Gorlov turbines, hold promise of more efficient but
inexpensive run-of-the-stream devices.

Answer to Question 2

We are not given information about the cost of the two refrigerators, but
(amazingly enough) many times the cost is not significantly different between different
models. Assume they cost the same amount. Then, over 13 years, the cost of the more
efficient model is,
(13 years) x (515 kWh/yr) x 0.10/kWh = (13 years) x 51.50/yr = 669.50
The cost of the average model is
(13 years) x (979 kWh/yr) x 0.10/kWh = (13 years) x 97.90/yr = 1272.70
You would have saved 1272.70 - 669.50 = 603.20 over those 13 years. It is extremely
unlikely that the more efficient could have cost that much more than the average model.
In any case, if the more efficient model is more expensive than the average model, you
would just subtract the extra cost from the savings listed above to find the actual savings.
Over the 19 yr mean refrigerator lifetime, the more efficient model would actually save
881.60 (minus the cost differential, if any) at an electricity cost of 0.10/kWh. If the
electricity cost were just 0.08/kWh, the net savings would be proportionally smaller,
705.28 over the 19 years, 482.56 over 13 years.

[ahriuashd]

Excellent

[Animal_Goddess]

Gracias!