104 Time September 23, 2019
Randall munRoe is a caRToonisT, auThoR, engineeR, scienTific TheoRisT and The cReaToR of The
web comic xkcd. Below are two tongue-in-cheek proposals for new ways to generate emissions-free energy—
both are clearly not viable, but perhaps they’ll inspire someone to come up with something better. After all, we
need all the ideas we can muster if we’re to reach zero emissions. —elijah WolfsonTectonic plates
The ground exerts a force over a distance, and
that equals energy. An inch of movement a year
isn’t much, but it has a virtually infinite force.
Could you harness it to generate electricity?
In theory, yes!
Suppose you built a pair of giant pistons on two
sides of a fault line created by two areas of crust sliding past each
other. As, say, southward- and northward-moving pistons approached
each other, they could compress a reservoir of fluid between them.
Escalators
Escalators give
energy to their
riders. When
you get on an
escalator and start
moving up ward,
the escalator
consumes extra
electrical energy
to turn the motors
that lift you. This energy is transferred to you in the form of potential
energy. If you turn around and slide down the railing back to the lower
level, you’ll arrive at high speed—having turned the potential energy
from the escalator motors, which you got for free from the escalator,
into kinetic energy.With the help of some simple mechanisms, you can turn that
potential energy into electrical energy instead. Escalators are really
just big metal waterfalls, and you can use the moving stairs to turn an
axle, just like a waterfall turning a waterwheel at a mill.A simple wheel with flat paddles
will interlock awkwardly with the
escalator. You can make it work
more smoothly by building a wheel
with curved paddles that mesh
with the escalator. If you shape
the paddles carefully, the wheel
can stay in constant contact with
the escalator without sliding.The amount of power you can extract from an escalator this way can
be substantial. The mechanical work an escalator does each minute
is simple to calculate—it’s equal to the peak number of passengers
per minute times weight per passenger times the escala tor’s height
times the acceleration of gravity. When fully loaded with people, a two-
story escalator might easily output 10 kilowatts of mechanical power,
much of which you could capture with a well-designed wheel. That’s
enough to run an entire house.An escalator waterwheel could extract significant amounts of energy,
but that also means it would cost the escalator owners significant
amounts of money. If you force an escalator to exert an extra
10 kilowatts of power for 12 hours a day,
that could cost the owners more than
$400 a month extra in electricity bills.
Needless to say, they probably won’t be
thrilled if they find out.The pressure on the fluid would build up over time and could be used
to drive a tur bine. This whole system is ridiculous and technically
infeasible for a lot of reasons. A big one is cost.
The “roots” of the structure that anchored the generator would need
to extend outward a great distance to enlist a lot of crust. Too small
an area of crust might just be
locked in place by the generator,
causing new fault lines to crack
around it. Of course, size presents
problems. If the roots were made
of steel and extended 5 km in
each direction, they would weigh
60 billion tons and cost around
$40 billion.
That’s a lot of money, but you’d be
saving about $1,100 per year on
energy costs, so you’d make your
money back in ... 36 million years.
Adapted from How To by Randall Munroe. Published by arrangement with Riverhead,
a member of Penguin Random House LLC. Copyright © 2019 by xkcd inc.Two bad ideas forgreen energy
By Randall Munroe