SWEDEN hopes to tap into a billion-year-old catastrophe to help heat homes in
Stockholm—and cut the country’s carbon dioxide emissions. A team from the
Royal Institute of Technology in Stockholm wants to extract geothermal energy
from a 10-kilometre-wide impact crater just outside Stockholm, partly covered by
Lake Mälaren. The idea is to reduce the amount of fossil fuel
used to power local heating systems.
Herbert Henkel, project leader at the institute, wants to use energy from the
crater to heat water that can be pumped around people’s homes. “It will
primarily be for winter heating,” he says. What attracts Henkel to the old
crater are the porous rocks beneath it, which were shattered by the meteor
impact. A free flow of water is vital for extracting geothermal energy, so the
first part of the project will measure permeability and drill test holes.
The thermal gradient under the crater is no greater than in many other places
in Sweden. But the researchers hope that the porous rock will extend to a depth
of two kilometres over a wide area. This far down it should be hot enough to
yield energy for local heating systems.
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No one has attempted to exploit impact craters before, says John Finger of
Sandia National Laboratories in New Mexico. Other groups have tried to use the
heat deep in volcanic craters. Fresh volcanic rocks are hot enough for electric
power generation, which requires a large temperature difference between the top
and the bottom of a geothermal well.
Winter heating will work with a much smaller temperature gradient, which
makes exploiting the impact crater feasible. In Sweden, electricity generation
is not a priority as the country has a surplus of nuclear and hydroelectric
power.
Building new geothermal systems can be expensive, but the Stockholm area
already has a network of heating pipes powered by three oil-fired plants. “If
you already had an existing piping system, and all you had to do is add hot
water, that would make a huge difference to the economics,” says Finger.
Henkel reckons the crater rocks could yield some 400 terawatt-hours of energy
in total, enough to supply about 70 per cent of the region’s residential heating
needs for many years.