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Une usine marémotrice... en Grande Bretagne

Article publié le 24 février 2009

Une usine marémotrice... en Grande Bretagne

Le monde commence à s’agiter ferme pour trouver de nouvelles sources d’énergie et diminuer nos émanations de CO2. Les uns se couvrent d’éoliennes à tout va, d’autres promeuvent le photovoltaïque et certains s’intéressent à nouveau à l’équipement en centrales hydrauliques de leur pays, quasiment abandonné depuis une bonne trentaine d’année. C’est le cas de la Grande Bretagne qui vient d’annoncer un projet... d’usine marémotrice !!

Une technique que l’on croyait abandonnée et sans espoir de retour devant le peu de cas qu’en faisait EDF, pourtant le seul opérateur au monde de cette technique avec l’Usine marémotrice de la Rance. Il est vrai que l’on avait cru savoir que le coût de maintenance en était très élevé du fait de l’action agressive du sable sur les pales des turbines. Et l’on était bien conscient qu’une telle installation avait un effet majeur sur l’écosystème de l’estuaire d’accueil.

Tout ceci ne semble pas effrayer nos amis britanniques qui disposent d’un site particulièrement propice sur l’estuaire de la Severn, la rivière qui sépare l’Angleterre et le Pays de Galles. Un estuaire particulièrement large entre Cardiff coté gallois et Weston Super Mare coté anglais puisqu’il peut atteindre 20 km et une hauteur de marée de 15 mètres d’amplitude. De quoi turbiner des tonnes d’eau de mer tous les jours !

Le projet est pharaonique puisqu’il prévoit d’y installer une usine d’une puissance équivalente à celle de 6 tranches nucléaires type EPR soit 8.6 gigawatts. Attention puissance et production d’électricité sont deux choses différentes, la différence étant qu’une centrale nucléaire peut fonctionner à pleine puissance 24 heures sur 24 alors qu’une usine marémotrice, liée aux marées, ne produit qu’une partie de son temps. Comme d’ailleurs une éolienne (25 % de son temps productif) ou un panneau photovoltaïque (50/70 % de son temps). Cela reste néanmoins une capacité de production très importante.

Le principe est le même que celui de l’usine de la Rance, la marée fait tourner les 216 turbines installées soit à la montée dans l’estuaire soit à la descente. Simplement la capacité de production est 35 fois plus importante. Il en coutera une vingtaine de milliards d’euros d’investissement à l’opérateur et le tonnage d’émissions de CO2 est prévu atteindre 7.2 millions de tonnes sur une durée d’exploitation de 120 ans soit seulement 60 000 tonnes par an soit 660 000 Euros de contribution au profit par an, une contribution marginale mais toujours appréciable à l’équilibre économique du projet.

Seul inconvénient, les associations écologiques hurlent contre l’impact de ce projet sur l’écosystème de l’estuaire de la Severn. Difficile de trancher entre la survie des poissons et oiseaux ou celle de l’espèce humaine. Le gouvernement britannique a néanmoins prévu sur le même site mais plus en amont des variantes moins pharaoniques avec des puissances comprises entre 0.6 et 1.4 gigawatts, des coûts d’investissements bien inférieurs, des émissions évitées de CO2 bien inférieures et moins de nuisances à l’écosystème.

A suivre pour le choix du projet final.

Thèmes

Energie Energies renouvelables

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votez :
par lio (IP:xxx.xx7.132.202) le 25 février 2009 à 16H16

la survie de l’espéce humaine est etroitement liée a celle des poissons et des oiseaux(et d’autres),mais j’ai l’impression que ça vous passe au dessus des genoux pardon de la téte ?

votez :
par Paganel (IP:xxx.xx8.146.203) le 13 mars 2009 à 07H51

Attention tout de même : l’énergie dite "des marées" eest en fait uniquement l’énergie cinétique de rotation de la Terre (ou plus exactement celle de l’inertie de la mer dans le système Terre-Lune, mais cela revient au même), ET S’IL Y A UNE ENERGIE NON-RENOUVELABLE, C’EST BIEN CELLE DE LA ROTATION TERRESTRE, JUSTEMENT. Les astronomes, gens très précis, ont déjà mesuré sur la quatorzième décimal le surcroit de ralentissement terrestre causé par l’usine de la Rance. Si dix mille usines se bâtissent et qu’on les fait tourner dix mille ans (ce qui est très peu par raport à l’histoire de l’humanité), le ralentissement attendra quelques pour cents. Non seulement l’ancienne vitesse de rotation de la Terre ne reviendra *jamais*, mais l’impact sur les phénomènes météorologiques est imprévisible. Tout ce que nous savons, c’est que plus une planète tourne lentement sur son axe et plus les phénomènes météorologiques y sont violents.

Mieux vaut sans doute s’orienter vers la géothermie que de jouer à l’apprenti-sorcier avec ces usines marémotrices. Sans rotation rapide de la terre, pas de cycle source chaude/source froide, et donc beaucoup moins de biomasse possible. Il faut sans doute y réfléchir.

(Accessoirement, le ralentissement terrestre a pour effet d’éloigner un peu la Lune, comme le montre la considération du couple d’inertie du système).

votez :
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votez :
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