| lundi 6 septembre 2010 SINTEF
There is a solution for the world's insatiable
energy needs. It is CO2-free and safe. And it's located right
under our feet.
Ever since Jules Verne wrote in 1864 about
a trip to the Earth's interior, people have dreamed of bringing up heat
from the centre of the planet. So far we have only scratched the surface,
but researchers are now beginning to work down into the depths.
The fact is that 99% of the planet has a temperature
above 1.000°Celsius. The heat is what's left over from when the Earth
was first formed, and there is more than enough of it for us to transform
it into energy.
"If we can drill and recover just a fraction
of the geothermal heat that exists, there will be enough to supply the
entire planet with energy – energy that is clean and safe," says Are
Lund, senior researcher at SINTEF Materials and Chemistry.
Inexhaustible source
Geothermal heat offers incredible potential.
It is an inexhaustible energy source that is nearly emission-free. Heat
energy is found in the different rock types that make up the Earth's surface,
and deeper in the crust. The deeper you get, the hotter it is.
Around one-third of the heat flow comes from
the original heat in the Earth's core and mantle (the layer closest to
the Earth's crust). The remaining two-thirds originate in radioactivity
in the Earth's crust, where radioactive substances continuously decay and
generate heat. The heat is transported to rock layers that are nearer the
Earth's surface.
Different depths
Geothermal energy that comes from 150-200
metres below the surface is called low temperature geothermal energy. At
these depths, temperatures hover between 6 and 8°C and can be extracted
with heat pumps, combined with an energy well. This type of geothermal
energy is exploited at a fairly large scale.
The Norwegian company Rock Energy wants to
be an international leader in geothermal heat and energy. A pilot plant
has been planned for Oslo that will collect heat from 5500 metres deep.
Temperatures from this depth can heat water to 90-95°C and can be used
in district heating plants. The pilot plant will be built in cooperation
with NTNU, which is studying the thermal aspects of the plant.
The plan is to drill two wells, an injection
well where cold water is pumped down, and a production well where hot water
flows back up. Between these will be so-called radiator leads that connect
the wells. The water is then exchanged with water in Hafslund's district
heating plant.
The normal lifespan for a well like this is
approximately 30 years. After that the rock will be so cooled by the cold
water that has been injected into the wells that it will no longer produce
enough heat. However, after 20-30 years, the heat will have built up again,
and the well can be used once more.
The Rock Energy facility will be a major step
forward in exploiting Norway's geothermal heat resources.
Supercritical water
However, if we want to reduce CO2
emissions and provide clean energy on a scale that will make a difference,
we will need go much further down into the Earth itself.
Researchers at NTNU, the University of Bergen
(UiB), the Geological Survey of Norway (NGU) and SINTEF believe this is
possible. In 2009, deep geological energy enthusiasts formed the Norwegian
Centre for Geothermal Energy Research (CGER), with partners from universities,
colleges, research institutions and the industry.
The researchers' goal is to reach depths of
10,000 metres or more to exploit deep geothermal heat. Drilling that deep
will enable wells to reach what is called supercritical water with a temperature
of at least 374°C and a pressure of at least 220 bar. That multiplies
by a factor of 10 the amount of energy you can extract from such an arrangement,
and the amount of geothermal energy produced can match that created in
a nuclear power plant.
But there is a very important difference:
Geothermal heat does not create radioactive waste. It is clean energy.
"If we manage to produce this kind of energy,
it would clearly be a ‘moon landing'. This is one of the few sources of
energy that we really have enough of. The only thing that we need is the
technology to harvest it," says researcher Odd-Geir Lademo at SINTEF
Materials and Chemistry.
Pros at 5.000 metres
Today's oil companies are making a good living
by extracting oil that is as deep as 5.000 metres, where temperatures are
as high as 170°C. Drilling any deeper than this results in a range
of engineering problems, both in terms of the drilling itself and materials.
Steel becomes brittle, and materials such as plastics and electronics will
be weakened or melt. Electronics operate normally only a short time at
temperatures hotter than 200°C. These problems will have to be solved
for the deep geothermal industry to be profitable.
Nevertheless, SINTEF scientists think that
Norway is in a unique position to capture geothermal heat.
"We have a strong and innovative oil industry
this country. Because the oil industry has wanted to develop oil and gas
deposits from inaccessible areas, drilling technology has evolved tremendously
over the past ten years. There are test wells for oil that go 12.000 metres
into the Earth. Knowledge from the oil and drilling industry may be used
in the future to capture geothermal energy," say Lund and Lademo.
The Norwegian drilling and oil and gas industries
all demand equipment that makes it possible to drill ever deeper at an
affordable cost. The oil fields that are being discovered now are generally
deeper and more complicated than before. Even though there have been a
number of wells in the world that have been drilled to 10-12.000 meters,
the technology does not yet exist to allow for precision drilling at these
depths.
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"We have to have a common commitment. Multidisciplinary
expertise is required. Here at Materials and Chemistry, we are working
with an internally funded project in which we are assessing SINTEF's overall
ability to contribute. The goal is to work on projects with industry and
the Research Council of Norway," Lund said, adding, "If research
and industry succeed in developing the materials and technology needed
to bring up the most difficult-to-reach oil, in the long run we will be
able to replace oil with geothermal energy for heating and electricity."
Available everywhere
One of the unique aspects of geothermal heat
is that it is found everywhere throughout the world. Call it a "democratic"
energy source that anyone can take advantage of, regardless of the conditions
at the Earth's surface, such as the weather.
How far down you have to drill into the Earth's
crust to reach the temperature that you're interested in varies from country
to country. This is because the crust varies in thickness, and controls
what is called the geothermal gradient. At more northerly latitudes, like
Norway, the temperature increases by about 20 degrees per kilometre into
the Earth's crust. In other parts of the world, it is 40 degrees per kilometre.
The average is around 25 degrees.
The United States, the Philippines, Mexico,
Indonesia and Italy are the international leaders in terms of producing
electricity from geothermal energy. Iceland comes in at a surprising 8th
place.
Volcanic Activity
The fact that Iceland is on the list at all
is because it is home to some of the most extensive volcanic activity in
the world – and consequently has access to a great deal of geothermal
energy. Volcanic eruptions are too uncontrolled to allow their heat to
be used for energy purposes. But weaker heat sources, such as geysers and
hot springs, are used extensively both in Iceland and other countries with
volcanic activity.
This places the country in a class by itself
when it comes to using geothermal resources. Since 1930, Iceland has used
geothermal energy for district heating, and today about 60% of the population
is connected to geothermal heating in some way.
Hundreds of holes have been drilled outside
of Reykjavik to harness geothermal temperatures between 100 and 150°C.
This warm water is transported to the capital through pipes with a diameter
of 35 cm. The pipes are buried under roads, so that they keep the roads
free of ice during the winter. Heat loss between the plant and Reykjavik
is just 5°C.
Playground in the land of the sagas
"They're now drilling for supercritical
water in Iceland. Geothermal heat is so readily available, the country
is essentially a laboratory and the biggest playground for the use of geothermal
energy. We're watching them closely to learn from their experiences,"
said Lund.
If geothermal energy is going to be produced
on a scale that makes a difference in terms of energy demand worldwide,
it will have to be produced everywhere - even without volcanic sources.
These kinds of geothermal energy plants could then be placed near towns
and energy intensive industries.
More and more people beginning to realize
that geothermal heating offers a viable energy alternative. The critical
question is whether the technology required for deep, safe and economic
drilling can be developed.
Enova hesitates
Enova, a government-financed energy efficiency
agency, is among the institutions and individuals who question the costs
associated with producing geothermal energy.
"Deep geothermal heat from thousands of
metres deep could be promising. But the cost picture here is still uncertain,"
said Kjell Olav Skjølsvik, a senior adviser at Enova.
The organization has not ranked deep geothermal
heat as a possible future energy source. "Many technologies are competing
for this title, and we consider it more likely that a future energy system
will use multiple sources and multiple technologies in a cost-effective
mix," says Skjølsvik.
However, Enova also recognizes the potential
in geothermal energy, and has therefore granted support to Rock Energy's
project in Oslo.
"We hope the project can help to clarify
how mature the technology is, and help us figure out how to calculate the
cost of deep geothermal heat in Norway," says Skjølsvik.
"It will succeed"
Odd-Geir Lademo and Are Lund are not discouraged
by these criticisms. They think it should be possible to unite industry,
researchers and government to find solutions that are needed to harness
the promise of geothermal heat.
"The oil and gas industry is conservative.
To begin to develop geothermal energy from ten to twelve thousand metres
deep will be expensive. But the benefits will also be enormous. That is
why the industry will eventually begin to invest. In the 1960s, we were
beginners when it came to pumping oil from the North Sea. Tackling that
challenge was a huge boost in many ways. As a nation, we bet and we won,"
says Lademo.
"I believe we can develop the knowledge
we need about materials to get down to 300°C in ten years time. It
might take 25 years or more of research and development to get down to
500°C," Lund said, with agreement from Lademo.
"We are convinced that this is possible.
But it requires us to further develop existing technology. To do that requires
money, a lot of money. Public funding is the key that's needed to get the
industry overall to invest. Geothermal energy is a unique opportunity for
the oil industry to develop in a new way. They will come to realize this,
it's just a matter of time." |
