ENERGIES RENOUVELABLES
sol(ID)aires
"HYDROGÈNE ÉNERGÉTIQUE"
2007
ENERGIES RENOUVELABLES
| A new kind of efficient, solar-powered
laser has been developed by researchers at the Tokyo Institute of Technology,
in Japan. They hope to use the laser to help them realize their goal of
developing a magnesium combustion engine. The researchers described the
new laser in a recent issue of Applied
Physics Letters.
The idea, says Takashi Yabe, a professor of mechanical engineering and science at the Tokyo Institute, is to make a powerful laser capable of combusting the magnesium content of seawater. In the process, large amounts of heat and hydrogen are given off. Magnesium has great potential as an energy source because it has an energy storage density about 10 times higher than that of hydrogen, says Yabe. It is also highly abundant, with about 1.3 grams found in every liter of seawater, or about 1,800 trillion metric tons in our oceans, he says. Moreover, the magnesium oxide resulting from the reaction can be converted back into magnesium, says Yabe. The catch? Recycling the magnesium oxide back into magnesium requires temperatures of 4.000 kelvins (3.726 ºC)--hence the need for a laser to generate such temperatures on a small spot. But for a magnesium combustion engine to function as a practical source of energy, the lasers need to be powered by a renewable energy source, such as solar power. Solar-pumped lasers already exist: they work by concentrating sunlight onto crystalline materials such as neodymium-doped yttrium aluminium garnet, causing them to emit laser light. Until now, however, most solar-pumped lasers have relied on extremely large mirrors to focus the sunlight on the crystal. |
Yabe and his colleagues have developed a compact
laser that offers a threefold improvement in efficiency over previous designs,
in terms of how much power it can deliver compared with the available sunlight.
This is partly due to the use of Nd:YAG crystals that are additionally doped with chromium, enabling them to absorb a broader range of light. Adding the chromium makes a greater proportion of the spectrum available, says Yabe: "Thus the efficiency from sunlight to laser is greatly enhanced." The other innovation of Yabe's laser is the use of a small Fresnel lens instead of large mirror lenses. Fresnel lenses reduce the size and amount of material needed to build a lens by breaking it into concentric rings of lenses. Typically, 10% of incident light is focused on the crystal, whereas with the Fresnel, it's around 80%. "In our case, we used only 1.3 meter squared and achieved 25 watts," says Yabe. Although this is only a threefold increase, the laser output exponentially increases with the increasing area. "So we are expecting 300 to 400 watts with the four-meter-squared Fresnel lens," he says. It's an unusual approach, says Sunita Satyapal, head of the Department of Energy's hydrogen-storage team, in Washington, DC. But it's not the first time that metals, such as magnesium, and water have been explored as a means of hydrogen production, she says. What is needed now is a total-efficiency budget for the entire system, says Satyapal: "The key issue is cost and total efficiency." There are much simpler ways of generating hydrogen using sunlight, such as by employing solar cells to split water using electrolysis, she adds. |
| If given the go-ahead, the energy
research centre would be located close to a Hydrogen Office building, also
proposed for the Methil area.
The facility would house a novel hydrogen production system which has the potential to become a world-leading renewable energy solution. The Scottish Enterprise Fife plans have been submitted to Fife Council. Fuel cell
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The energy centre is one of a number of potential
projects earmarked for the emerging energy hub at Methil and we are confident
that, if given the green light, the project will deliver significant economic
benefit not only for Fife, but for Scotland as a whole."
It is hoped the project will become one of the world's first fully integrated alternative energy projects, combining traditional wind and geothermal source heat pump technology with hydrogen and fuel cell energy storage techniques. The project aims to use surplus renewable electricity to convert tap water into hydrogen, which researchers say is a sustainable means of storing energy. The quantities of hydrogen stored by the project would be small and comparable in energy terms to the petrol carried by three family cars. |
| Le laboratoire Energy's Brookhaven
National Laboratory a construit le premier réacteur d'essai
dans lequel les bactéries produisent de l'hydrogène gazeux
en présence d'oxygène.
Jusqu'à aujourd'hui, la production d'hydrogène par des bactéries anaérobies semblait impossible car celles-ci meurent en présence même minime d'oxygène dans le milieu. Cependant, le chercheur Niels van der Lelie et son équipe ont récemment mis en évidence que la bactérie Thermotoga neapolitana, associée à des composés biochimiques, est capable de se protéger contre la toxicité de l'oxygène tout en produisant de l'hydrogène à partir de sucres. |
La bactérie Thermotoga est dite extremophile,
c'est-à-dire qui se développe dans des conditions extrêmes
comme les sources thermales dans ce cas précis.
Elle est capable de décomposer les hydrates de carbone sans utiliser d'oxygène. Ces bactéries peuvent produire une grande quantité d'hydrogène à partir de déchets agricoles, à une température de 167°C, sous pression atmosphérique et avec un faible taux d'oxygène. Selon le chercheur, la découverte de cette bactérie est importante pour le marché de l'hydrogène, car elle permettra de construire des bioréacteurs agricoles capables de produire de l'hydrogène de facon continue et peu onéreuse. |
| Les expérimentations menées
dans le parc expérimental de Sotavento à Monfera devraient
débuter très prochainement. Leur but: obtenir de l'hydrogène
à partir de l'eau en utilisant l'énergie éolienne.
Les essais qui devraient se poursuivre tout au long de l'année sont
financés à hauteur de 400.000 euros par le conseil de l'industrie
et du gaz naturel.
On espère pouvoir fournir des données précieuses sur la possibilité d'emmagasiner l'énergie éolienne en la convertissant en hydrogène stocké dans des réservoirs. Pour obtenir l'hydrogène, l'énergie générée par les aérogénérateurs sera conduite jusqu'à un électrolyseur. Cet appareil décompose l'eau à l'aide d'un courant électrique en dihydrogène et en oxygène. L'oxygène sera relâché dans l'atmosphère et l'hydrogène sera conservé et utilisé pour obtenir de l'électricité réinjectée ensuite dans les turbines éoliennes. |
Si les tests sont concluants, les parcs éoliens
pourraient alors absorber les surplus d'énergie en cas de forte
production et produire de l'électricité malgré l'absence
de vent.
On pourrait aussi gérer plus précisement la production éolienne, afin de l'adapter à la demande du réseau. Pour en savoir plus, contacts :
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