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II/ Geothermal energy is the solution for the future

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.

     "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."

I/ La géothermie, un don de la Terre
Xavier Ducarme

     Le car serpente depuis plus d'une heure dans la montagne. Le paysage de la forêt d'ifs est maintenant traversé d'un réseau d'interminables canalisations de gros calibre. Une vague odeur soufrée plane dans l'atmosphère. Et puis, au détour d'un virage, de puissantes colonnes de vapeur s'échappent du sol.
     C'est ici, à Los Azufres, à 3.000 m d'altitude, au beau milieu de la cordillère néovolcanique, à quelque 200 km à l'ouest de Mexico, que s'étend sur plus de 30 km², l'une des rares centrales géothermiques de dimension industrielle dans le monde. Ici, pas besoin de pétrole, de gaz, de charbon, d'uranium ou même de bois pour produire de la vapeur et faire tourner un générateur électrique. Non, ici, la vapeur sort directement du sol, sous une pression suffisante pour entraîner une turbine et produire directement de l'électricité, sans produire le moindre gaz à effet de serre. "Un don de la Terre", commente Frédéric Sauze, directeur de la branche géothermie d'Alstom Power, le géant français de l'énergie qui a construit sur le site quatre nouvelles unités de production électrique clé sur porte, pour une puissance totale de 100 mégawatts. L'ensemble de la zone comporte 14 unités, pour une puissance totale de 197 MW, soit l'équivalent d'une vingtaine de grosses éoliennes. "A la différence qu'ici, les turbines tournent en permanence. Une éolienne, s'il n'y a pas de vent, ne produit pas le moindre kilowattheure" commente encore M. Sauze.
     Bref, il y a ici, de quoi alimenter en électricité une bonne partie de Morelia, la ville voisine d'un million d'habitants.
     La zone de Los Azufres n'a pas été choisie au hasard. L'importante activité sismique des lieux y fait affleurer de grandes quantités d'eau chaude, que l'on peut facilement capter en creusant des puits. Il y en a 59 dans la zone. La puissante vapeur qui s'en dégage est canalisée grâce à un écheveau de pipelines vers les unités de production. Non sans avoir été lavée de ses impuretés, histoire de ne pas abîmer les précieuses et précises ailettes des turbines de générateurs. Une partie de ce qui n'est rien d'autre que de l'eau en ébulition s'échappe alors dans l'atmosphère, une autre se condense et est réinjectée dans le sol. Car si la source est abondante, elle n'est pas, si l'on n'y prend pas garde, inépuisable. La production doit en effet être calibrée à la mesure des réserves d'eau chaude que recèle la zone.

          Si l'on exploite trop de vapeur, les réservoirs souterrains d'eau chaude n'ont pas le temps de se régénérer et la ressource perd alors de sa puissance. C'est ce qui est d'ailleurs arrivé à la plus grande centrale du monde, "The Geysers", au nord de San Franscisco, au Etats-Unis. Ses exploitants ont été trop gourmands. Quatre fois plus grosse et étendue que Los Azufres, la centrale californienne a constaté récemment un appauvrissement de sa réserve, consécutif à une surexploitation de la nappe. "Mais si on gère convenablement la production, si on veille à l'équilibre entre l'exploitation et la capacité de régénération, la source d'énergie peut rester constante durant des millénaires". Si on est trop pressé, trop avide, elle s'essouffle, et il faut de nombreuses années avant qu'elle ne retrouve son régime naturel.
     C'est exactement ce que veut éviter le Mexique. Le quatrième producteur mondial d'électricité géothermique mise sur cette ressource providentielle que seuls quelques rares pays privilégiés peuvent exploiter. Pour réduire de 50% ses émissions de CO2 d'ici 2050 comme il l'a annoncé, le pays se doit d'utiliser toutes les énergies renouvelables qui sont à sa disposition. Le potentiel de son sous-sol lui autorise d'envisager un triplement de la production. Un beau challenge. Mais qui, à l'échelle d'un tel pays, reste une goutte d'eau. Le très polluant charbon, toujours lui, pas cher et abondant devrait continuer à produire quelque 60% de l'électricité mexicaine.
Première fois
     C'est à Larderello, dans un petit village de Toscane où coulent des sources chaudes et soufrées déjà appréciées dans l'Antiquité par les Romains, que la chaleur de la Terre fut pour la première fois utilisée pour produire de l'électricité. En 1904, le prince Ginori Conti parvient à allumer cinq ampoules grâce à la vapeur naturelle. Un an plus tard, une première centrale expérimentale de 20 kW voit le jour. Aujourd'hui, la centrale toscane développe une puissance de 800 MW, soit l'équivalent d'un réacteur nucléaire de taille moyenne. Le tout au pétrole oblige, Larderello sera restée pendant un demi-siècle la seule centrale géothermique du monde. Ce n'est en effet qu'en 1958, à Wairakei, dans une zone de geysers de Nouvelle-Zélande, et ensuite au Mexique et en Californie, que seront construites de nouvelles centrales électriques industrielles.