Iceland review - 2013, Side 82

80 ICELAND REVIEW
ing, Einar replies, “Undoubtedly examples
can be found whereby utilization of geo-
thermal energy has changed over time. If a
lot is pumped up, the water level can lower
in the area. A new level of equilibrium is
often reached, although occasionally the
water cools when the water level diminishes
because cold water streams in due to a reduc-
tion in the geothermal reserve. One must
respond to these conditions, for instance by
reducing pumping or even by insulating the
boreholes better.”
The use of geothermal energy for district
heat production is generally sustainable, as
the heat is used directly and environmental
effects are insignificant.
gEothErmAl For ElEctricity
When geothermal energy is used for produc-
ing electricity, the situation is more complex.
Only high-temperature areas are used as a
source. And it’s difficult to predict how a
given geothermal area will respond when
exploited for electricity production. Experts
can drill boreholes and assess how much
energy can be tapped, but in the case of a
large area any estimates are pure guesswork.
The geothermal power plants at Svartsengi
and Nesjavellir in Southwest Iceland both
produce a combination of electricity and
hot water for district heating. Both were
developed in stages and neither has caused
problems from an environmental point of
view. Both sites were researched thoroughly
beforehand.
When an environmental impact assessment
(EIA) was carried out for two geothermal
power plants, including Hverahlíð, not far
from the Hellisheiði plant, the National
Energy Authority (Orkustofnun) sent the
Icelandic National Planning Agency a letter
in which they pointed out that considerable
uncertainty reigned concerning the com-
bined effect of the proposed development of
the geothermal resource in the area around
Hellisheiði, saying that experience has shown
that the nature of the resource places limits
on its sustainable utilization.
Because the operator of the Hellisheiði
plant, Reykjavík Energy, is bound by contract
to provide a constant amount of energy, steam
from the Hverahlíð site will probably be piped
overground to Hellisheiði to make up the
deficit. Scientists believe this will present an
opportunity to find out how the geothermal
area as a whole will react when energy is
tapped in different areas. The Hverahlíð site
had previously been scheduled for construc-
tion as soon as funding was available, but
Reykjavík Energy had been forced to delay
construction of the plant until a solution has
been found to the excessive levels of hydrogen
sulfide that emanate from the Hellisheiði plant
due to the vicinity of the magma chamber to
the geothermal system. This will take time.
One way of recharging a system is to rein-
ject waste steam back into the ground. This
has worked well with the Svartsengi plant,
but when waste steam has been reinjected
into the ground to a depth of 800 m (2,620
ft) in an attempt to recharge the energy
reserves around Hellisheiði, the experiment
has worked in some boreholes but not in
others. The process has also caused a series of
earthquakes.
thE ProBlEm oF hydroPowEr
The original hydropower stations tapped lakes
such as Þingvallavatn and Mývatn, which have
no glacial input. Some sort of water collection
system is needed in these cases, such as a reser-
voir. However, “this sort of power plant would
not be agreed these days due to its environ-
mental impact,” says Sveinbjörn Björnsson
from the National Energy Authority.
The glacial rivers that are now used for
hydropower in Iceland carry a great deal of
sand and silt. “Silt deposits are not a problem
for power stations that should last for 200-300
years. After that the glaciers will have changed
anyway if current climate trends continue,”
Sveinbjörn continues.
With hydropower stations, the size of the
plant is not important when it comes to sus-
tainability. Ragnheiður Ólafsdóttir, environ-
mental manager at Landsvirkjun, the national
power company, says they are working with
the Hydropower Sustainability Assessment
Hellisheiðarvirkjun.
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