Energy and Human Ambitions on a Finite Planet, 2021a

10 Renewable Overview 171
away from physics <strong>and</strong> address how all this new information might fit
into future plans at societal <strong>and</strong> personal levels.
10.6 Problems
1. Based on what you already know or suspect about the alternative
energy sources listed in Section 10.1, which ones do you suspect 30
are pollution free (no emissions, no waste)?
2. Based on what you already know or suspect about the alternative
energy sources listed in Section 10.1, which ones do you suspect 31
have no negative environmental impacts? Explain your reasoning.
3. Which of the truly renewable (“Yes” without asterisk) entries
in Table 10.1 are limited (finite) in terms of the scale 32 we could
achieve on Earth (explain the nature of the limit), <strong>and</strong> which are
not limited (<strong>and</strong> why)?
30: Don’t worry about correctness, as this is
an opportunity to think <strong>and</strong> gauge current
underst<strong>and</strong>ing.
31: Don’t worry about correctness, as this is
an opportunity to think <strong>and</strong> gauge current
underst<strong>and</strong>ing.
32: . . . not how long it can last; how much
power is available
4. Which four entries in Table 10.1 do not ultimately trace entirely to
solar energy input to Earth?
5. If, for some terrible reason, the sun ceased shining <strong>and</strong> humans
managed to survive for 1,000 years longer, 33 what options would
be left for obtaining energy?
33: It’s nearly impossible to imagine that
survival is at all realistic in this dire situation.
6. About 30% of the 1,360 W/m 2 solar power arriving at Earth
is immediately bounced back without a trace. Of the part that
remains, when distributed/averaged around the whole sphere, 34 34: account for projected vs. total surface
what is the average energy deposition rate per square meter into
area
the earth system?
7. Based on the numbers in Table 10.2, Figure 10.1, <strong>and</strong> in the text,
what fraction (in percent) of all biological activity on Earth do (all)
humans represent, from a metabolic energy st<strong>and</strong>point?
8. Based on the numbers in Table 10.2, Figure 10.1, <strong>and</strong> in the text,
what fraction (in percent) is human societal energy production (all
activities; fossil fuels, etc.) compared to all biological activity on
the planet?
9. What fraction (in percent) of the solar energy that is absorbed by
Earth’s surface goes into evaporation (the hydrological cycle; refer
to Table 10.2, <strong>and</strong> Figure 10.1)?
10. If we add up the five smallest pieces in Table 10.2, what fraction
(in percent) does this set of energy flows represent in comparison
to the total solar energy absorbed by the earth system?
11. The percentages of absorption <strong>and</strong> reflection in Figure 10.1 represent
averages over weather conditions. On a clear day with the
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.