Energy and Human Ambitions on a Finite Planet, 2021a

10 Renewable Overview 172
sun overhead, a solar panel has access to more light than the 48%
depicted reaching the ground. If we can also capture the portion
that on average is reflected by the ground <strong>and</strong> clouds, 35 what
might we expect for the rate of energy reaching the ground (in
W/m 2 ) if the input at the top of the atmosphere is 1,360 W/m 2 ?
35: Recall, it’s a clear day; no clouds.
12. Similar to Example 10.3.2, how much warmer would you expect
36: i Water has a density of 1,000 kg per
a 10 cm deep puddle of water 36 cubic meter <strong>and</strong> a specific heat capacity of
to get after an hour in full sun,
4,184 J/kg/ ◦ C. Make up whatever area you
if the water absorbs all the energy <strong>and</strong> does not lose it to the want; the answer should be the same for
environment?
any pick.
13. Comparing Table 10.2 <strong>and</strong> Table 10.3, what is the most striking
mismatch, 37 in terms of large potential vs. small contribution to
U.S. energy consumption?
37: In other words, for those sources that
can be matched within the tables, which
st<strong>and</strong>s out as the most underutilized relative
to its input numbers?
14. In one day, a typical residential solar installation might deliver
about 10 kilowatt-hours of energy. Meanwhile, a gallon of gasoline
contains about 37 kWh of thermal energy. But the two ought not
be directly compared, as burning the gasoline inevitably loses a
lot of energy as heat. Correcting the solar output to a thermal
equivalent, 38 how many gallons per day of gasoline could it 38: i Use the 37.5% factor discussed in
the text.
displace?
15. The U.S. occupies about 2% of Earth’s surface area, thus collecting
only part of the 83,000 TW absorbed at the surface. Compare the
amount of solar power received by the U.S. to the total renewable
power in Table 10.3. 39 By what factor are we “underutilizing” the
solar input, under the simplifying assumption that we could use
all of it?
39: . . . since it’s almost all solar in ultimate
origin
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.