Energy and Human Ambitions on a Finite Planet, 2021a

16 Small Players 278
heat to diffuse in, so we’d have to keep moving down, year after year.
This would mean completely replacing the collection network (whatever
comprises it—this is all fantasy) every few years. It’s ludicrous to imagine
we would endeavor to go to such extremes, plowing through the deep
earth to remove every scrap of thermal energy in a massive never-ending
effort. 9 Such a colossal scheme makes oil drilling seem like child’s play.
9: It would not be surprising if the EROEI
is abysmally low or even a net energy drain.
Granted, as one drills deeper, the thermal energy goes up <strong>and</strong> the
efficiency increases as ΔT climbs. The result is quadratic, in that the
energy yield 3 km down is 9 times that at 1 km down. 10 At the same time, 10: . . . because the hotter rock contains 3×
drilling gets more challenging <strong>and</strong> at some point exceeds the current more thermal energy <strong>and</strong> that energy can be
converted to electricity 3× more efficiently
state of the art. By the time the temperature reaches 150 ◦ C—which is
thought of as a minimum viable temperature for traditional geothermal
ventures—drilling technology runs into limitations.
Box 16.2: There Will Be Hype
As long as an idea is not outright impossible, the world is big enough
<strong>and</strong> competitive enough that enterprising individuals will be able to
generate interest <strong>and</strong> investment in ideas that seem viable <strong>and</strong> can be
touted to have great promise. Whether that idea is truly capable of
benefiting humanity as a “good” idea is not fully evaluated. Instead,
if it can make money in the short term, 11 then it may get a green light.
So be wary of claims by people or companies whose financial interests
lie in the perception of success <strong>and</strong> promise. Even media coverage
that should be objective is often quantitatively sloppy, 12 <strong>and</strong> has a
much easier time finding enthusiasts willing to devote time <strong>and</strong>
quotes than non-enthusiast experts who are too busy pursuing their
own projects to waste time poking holes in shoddy ideas.
11: ...oratleast attract investment
12: . . . lacking a staff physicist
16.1.3 Geothermal Reality
Enough, then, about “pipe dreams” of massive geothermal exploitation
on a planetary scale. Geothermal energy is not all fantasy, as some places
are able to capture significant energy from this resource.
In a few locations, hot magma is brought near the surface, offering rare
cracks of access to high temperatures. An electrical power plant, as
depicted in Fig. 6.2 (p. 90), does not care particularly where the thermal
energy derives, as long as it’s hot enough to make steam. The ideal site
has:
◮ magma near the surface—volcanic regions, for instance;
◮ fractured rock above the magma in which water can flow;
◮ water temperatures in excess of 180 ◦ C (under pressure);
◮ a caprock above the fractured rock, able to trap pressurized steam.
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.