Iceland's secret power - Jean-Baptiste P. Koehl
While the weather in Iceland is
often cold, wet, and windy,
a nearly endless supply of heat bubbles
away below the surface.
In fact, almost every building in the
country is heated by geothermal energy,
in a process with virtually
no carbon emissions.
So how exactly does this renewable energy
work?
Between the Earth’s core and its crust
is a mixed layer
of solid and partially molten rock
called the mantle.
Temperatures here range
from 1,000 to 3,500 degrees Celsius.
Some of this heat comes from the
radioactive decay of metals.
But much of it comes from Earth’s core,
which has been radiating energy
since the planet formed
over four billion years ago.
While the mantle moves slowly,
circulating roughly 40 kilometers
below the Earth’s crust,
there are places where
it surges closer to the surface.
Here, the magma forms pockets
and veins in the ground,
heating underground rivers and pools
to temperatures reaching 300 degrees.
Controlling heated water is at the heart
of harnessing geothermal energy,
and there are two primary models
for how to do it.
One is to build a geothermal power plant
which uses these hot, deep pools
to produce electricity.
First, engineers drill a well several
kilometers into permeable rock
like sandstone or basalt.
As the hot, highly pressurized groundwater
flows into the well,
the rapid change in pressure
and temperature
produces huge amounts of steam.
This steam then turns the blades
of a turbine to generate electricity.
Finally, the remaining cooled water
and condensed steam
are injected back into the ground
to create an open loop
that provides electricity
without losing water.
However, we don't have to drill this deep
to take advantage of the planet's heat.
Thanks to solar radiation,
dirt just 1.5 meters deep can reach
temperatures over 20 degrees Celsius.
Geothermal heat pumps pipe water
or antifreeze liquid
through this layer of earth
to siphon its energy.
These liquids are then pumped
through local infrastructure,
dispersing their heat before
moving back through the ground
to absorb more energy.
While external electricity is needed
to operate the pumps,
the energy provided is far greater
than the energy used,
meaning this process is also
a sustainable loop.
In fact, geothermal heat pumps
are both cheaper to operate
and at least two times more energy
efficient than fossil fuel equivalents.
Whether geothermal energy is radiating
just below our feet,
or heating water several kilometers deep,
the planet is constantly radiating heat.
Averaged across one year,
Earth gives off roughly three times more
energy than humanity consumes.
So why does geothermal only account
for 0.2% of humanity’s energy production?
The answer has to do with heat,
location, and cost.
Since geothermal heat pumps rely
on the consistent heat
found in shallow earth,
they can be implemented almost anywhere.
But geothermal power plants require
tapping into
high-temperature geothermal fields;
regions hotter than 180 degrees and
typically several kilometres underground.
These high temperature zones
are hard to find,
and drilling this deep for just one
of the several wells a plant will need
can cost up to $20 million.
There are regions with shallower
geothermal fields.
Iceland and Japan are near active
volcanoes and tectonic plate boundaries,
where magma rises up through the crust.
But these same factors also make
those regions prone to earthquakes,
which can also be triggered
by intensive drilling.
Furthermore, while geothermal energy
is clean and renewable,
it’s not entirely harmless.
Drilling can release vapors containing
pollutants
like methane and hydrogen sulfide.
And drilling tools that use pressurized
water can contaminate groundwater.
Fortunately, new technologies are emerging
to meet these challenges.
Emission control systems
can capture pollutants,
and electromagnetic monitoring can
help detect seismic risks.
We're also uncovering entirely new
sources of geothermal energy,
like pockets of magma
in mid-ocean volcanoes.
So if we can safely and responsibly tap
into the heat sustaining our planet,
we might be able to sustain
humanity as well.
