Energy and Human Ambitions on a Finite Planet, 2021a

10 Renewable Overview 169
of 1,000 J/kg/ ◦ C under full sun, we can proceed as follows.
The table will absorb 1,000 J per second, 19 <strong>and</strong> therefore receives
600,000 J over the course of ten minutes. Multiplying the specific
heat capacity by the table mass means the table absorbs 20,000 J for
every 1 ◦ C of temperature rise, <strong>and</strong> therefore would climb 30 ◦ C in 10
minutes, in this case. That’s a little unrealistically high, because a real
table would also have cooling influences from the air <strong>and</strong> infrared
radiation. But the main point is to show how absorbed sunlight heats
things up—like the Earth.
19: Because a Watt is a Joule per second <strong>and</strong>
the table area is 1 m 2 ; the black property
essentially means that it absorbs all light
that hits it.
Box 10.2: Making New Fossil Fuels
We know from Chapter 8 that fossil fuels get their energy from ancient
photosynthesis trapped in buried plant matter. 20 We also now have a
figure for how much solar power goes into photosynthesis: 100 TW.
We can compare this to the power that goes into making new fossil
fuels right now by noting that the entire fossil fuel resource contains
roughly 21 10 23 J (page 127), <strong>and</strong> formed over something like 100
million years, or about 3 × 10 15 seconds. Dividing the two gives a
power of about 3 × 10 7 W, or 30 MW. 22
Three neat insights come out of this. First, we currently burn fossil
fuels at a rate of about 15 TW, which is 500,000 times faster than they
are being replaced! It’s like short-circuiting a battery in a dramatic
explosion of power. Imagine charging a phone for 2 hours <strong>and</strong>
discharging it 500,000 times faster: in 0.014 seconds! Now look at the
extravagant lights of Las Vegas: should we be proud of the blaze of
glory or appalled? 23
Secondly, out of the total 100 TW photosynthetic budget on Earth, only
30 MW gets captured as fossil fuels, which is one part in three-million.
Therefore, the chances that any given living matter on the planet
today eventually ends up converted to fossil fuels is exceedingly slim.
Finally, if we only used fossil fuels at a rate of 30 MW, 24 , then we could
consider fossil fuels to be a renewable resource, as the sun/geology
will slowly make more! So whether or not something is renewable
also relies on the rate of use not exceeding the rate at which it is
replenished.
20: In some cases, animals ate the plants
first, but the energy starts in plants.
21: It is not important to nail down precise
numbers for this exercise.
22: For reference, a single large university
consumes energy at about this rate.
23: Also coming to mind is the Big Bay
Boom in San Diego, July 4, 2012, when the
entire fireworks display that was meant to
last 15–20 minutes all went off in a few
dazzling seconds. LMAO. Best ever!
24: This amount of power could supply
only a single campus-sized consumer on
Earth.
10.4 Renewable Snapshot
Table 7.1 (p. 106) already gave an account of the mix of energy use in
the U.S., including many of the renewables. This section revisits those
numbers, in slightly more detail.
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.