N°30 I quarterly I july 2013 Focus | 19 w (e.g., behind a hydroelectric dam) at a higher altitude. Pumped-Storage Hydroelectricity (PSH) power plants temporarily store electricity in the form of potential energy. Retrieving it is simply a matter of gravity: the sluices are opened, letting the water from the reservoir flow through turbines that generate more electricity. Six large PSH power plants are currently operational in France, with an installed capacity of about 5 gigawatts (5 GW), but the country’s geographical characteristics make it difficult to envision more installations of this type. The Compressed Air Energy Storage (CAES) technique uses a similar approach, but with air stored below ground. Excess electricity is used to compress air, which can be released later to power turbines and retrieve electricity as needed. “For large-scale storage, another method consists in using giant batteries—or battery arrays—to transform electrical energy into chemical energy and vice versa,” Dollet explains. One such system was installed in Réunion Island in 2010: a high-capacity sodium-sulfur battery capable of releasing 1 MW for 7 hours. But the extensive deployment of electrochemical storage technologies is hampered by several problems, primarily linked to the materials themselves, such as their durability or their ability to be recycled. “This is also an issue in transportation systems, which call for the development of powerful yet lightweight batteries,” Brault adds. TECHNICAL OBSTA CLES The other two main energy vectors, heat and hydrogen, are somewhat easier to store than electricity. Research is underway to develop materials capable of storing high-temperature heat (ceramics, vitrified asbestos-containing wastes, etc.) or fixing hydrogen (hydrides, etc.). Nonetheless, as Brault and Dollet point out, “in the field of energy storage, many scientific and technical obstacles remain. Certain technologies are relatively mature, while others are only just emerging.” CNRS is striving to overcome these barriers and share scientific findings with industry. “Our organization is a key player in energy storage research and one of the four founding members of the French National Alliance for Energy Research Coordination (ANCRE),4” Dollet emphasizes. “By its very nature, energy is a highly multidisciplinary field of investigation, calling upon engineering, chemistry, and physics, but also the life sciences, humanities, social sciences, and many other disciplines. With its 10 Institutes, CNRS not only has expertise in these areas, but also an operational scope that ranges from fundamental research to industrial innovations.” In fact, the CNRS Mission for Interdisciplinarity has just launched an important challenge on “Energy Transition” to encourage the exploration of new research avenues while systematically integrating the social consequences, environmental impact, and availability of the various resources. The problem of energy storage will be central to this initiative. F. D. 01. Source: SOeS (Service de l’observation et des statistiques), Bilan énergétique de la France pour 2011. 02. G roupe de recherches sur l’énergétique des milieux ionisés (CNRS / Université d’Orléans). 03. Procédés, matériaux et énergie solaire (CNRS / Université de Perpignan V ia Domitia). 04. A lliance nationale de coordination de la recherche pour l’énergie (www.allianceenergie.fr). Contact information: Pascal Brault > pascal.brault@cnrs-dir.fr Alain Dollet > alain.dollet@cnrs-dir.fr POT ENTIAL ENERGY. Internal energy of a system subjected to a force (gravitational, mechanical, molecular, etc.). 03 The Verney dam and lake in eastern France are part of a Pumped-Storage Hydroelectricity (PSH) power plant that stores electrical energy. Until the storage problem is solved, renewable energy from hydrokinetic turbines (01) or from wind turbines and solar panels (02) will not be deployable on a large scale. 01 02 03 © F. Od oux/EDF © Eyematri x/fotoli a ENERGY TRANSITION. The conversion from an energy model based on the largescale consumption of fossil fuels to a more ecologicallysustainable model.
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