Les énergies renouvelables sont-elles décentralisées? / Are renewable energies decentralized?

Renewable energy sources are often presented as decentralized. Such a representation is very widespread in the media, and is popularized by writers such as Jeremy Rifkin. The possibility of collecting free energy from the environment, thus getting rid of large industrial companies is of course  most appealing. Unfortunately, reality is, for the time being, quite different. Hydraulic and biomass energy do not follow such a logic. The Three Gorges Dam in China is one of the largest human installations ever made. Windwill farms now gather frequently more than a hundred giant windmills. They require an expensive transmission network for transporting the intermittent electricity production. One day, perhaps, if new disruptive storage systems are developed, this situation might change. It is important to carry on research in that direction. But it is better to avoid illusions, so frequently encouraged by the media that public opinion becomes convinced that they correspond to the current situation.

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Les énergies renouvelables sont le plus souvent présentées comme décentralisées. Ceci correspond à la représentation, popularisée par des auteurs comme Jeremy Rifkin, de la possibilité pour chacun de générer sa propre énergie. Cette représentation est séduisante, car chacun rêve de devenir autonome et indépendant des grandes compagnies énergétiques. Pouvoir capter sa propre énergie à l'aide de quelques capteurs,  éviter les problèmes associés aux énergies fossiles semble la solution idéale. Malheureusement, la réalité est pour le moment assez différente. 

Le stockage d'énergie, condition de déploiement des énergies renouvelables / Energy storage as a prerequisite for renewable energy sources deployment

An extensive use of renewable energy sources requires finding an appropriate solution for energy storage. Renewable energy sources, such as wind and solar, are intermittent, and therefore some kind of back-up is needed for meeting the demand.  It can be provided by a gas-fired combibed cycle power-plant, but for increasing the penetration of renewable energy sources, while reducing the use of fossil fuels, some kind of energy storage system is needed. Large capacity storage is provided by pumped hydro-storage systems, but they are limited by the number of appropriate natural sites and the large size of the installations. In such a case, the storage location is generally located far from the production site. Therefore, large electricity transport costs are involved, together with resulting energy losses.  Such systems are clearly not appropriate for short duration intermittencies.  Other storage systems , such as batteries or flywheels,  are then required. Energy storage is quite costly. As practised now, it can represent 50 to 150 €/ MWh. These figures do not include the cost of electricity transportation. It is therefore a priority to develop new more cost-efficient energy storage systems. It is especially important to develop systems which could be cost-effective while being displayed near the production site. Liquid phase chemical systems, compressed air storage systems are potential candidates, but no option can  be considered as wholly satisfactory and energy storage remains until now the main hurdle to overcome for developing renewable energy sources.  

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Un recours très étendu aux énergies renouvelables implique de résoudre un problème particulièrement critique qui est celui du stockage d'énergie. En effet les énergies renouvelables, éolien et solaire sont intermittentes. Le vent peut s’arrêter et souffle à des vitesses très variables. Le rayonnement reçu du soleil est aussi très variable et s'annule la nuit. L’intermittence des systèmes de production d’électricité utilisant une énergie renouvelable (solaire, éolien), peut être compensée en modulant la puissance d’une centrale thermique opérant en back-up (telle qu’une centrale au gaz à cycle combiné). Pour augmenter le niveau de pénétration des énergies renouvelables, il faudra dans l’avenir recourir à des systèmes de stockage d’énergie de grande capacité.