Here is an optional exercise for you to contemplate over the holiday weekend. (It might make for a good final exam question, hint, hint).

1. The world consumes about 500 quads of energy today

2. Projections are that the world will consume 700 quads by 2030

3. Energy efficiency (EE) can be thought of as the inverse of energy intensity (EI) -- that is GDP/TE rather than TE/GDP -- so an increase in energy efficiency is equivalent to a decrease in energy intensity.

4. In the Kaya Identity CO2/GDP equals the product of energy intensity and carbon intensity -- CO2/GDP = TE/GDP * CO2/TE

5. Using your new-found appreciation of Excel and exponential growth equations, please calculate the rate of efficiency gains necessary to offset the projected increase in energy consumption by 2030 (#2 above)

6. Do the same thing for a 30% reduction in energy consumption from 2011

7. If the world consumed 355 quads in 1990, how do your projected rates of efficiency gain compare with reductions in EI from 1990-2011?

8. Convert your numbers in #5 and #6 into (a) carbon dioxide emissions and (b) nuclear power plants equivalent

9. What does this math say about the potential for efficiency to contribute to emissions reduction goals? If not efficiency, then what? (Hint look at the Kaya Identity)

10. BTW, the numbers in #1 and #2 leave 1.5 billion people in the dark with no energy access. So redo the exercise assuming (a) these people gain energy access at 20% of today's per capita US level (i.e., add 100 quads to #2), (b) these people gain energy access at 50% of the 2011 US level (i.e., add 250 quads to #2).

Understanding these numbers is, I think, a prerequisite to having a complete understanding of the role of efficiency gains in the debate over emissions.

To be clear on my views -- from TCF and the magazine article that I shared with you will know that I think that (a) energy efficiency is a very good thing and should be pursued, and (b) it is very limited in its potential to contribute to goals for emissions reductions. The math exercise above will help you to understand why I have come to this conclusion.

## 02 September 2011

### Energy Efficiency and Carbon Emissions: Class Assignment

Here is the assignment I gave my students in my graduate seminar on energy efficiency, motivated by this well done article: