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What to do with electricity generated by wind and sun, which is not used immediately in times of reduced power consumption? In order to integrate renewable energies fluctuating in a sustainable energy system, it is necessary to find ways to store excess energy produced. It is already possible to store electricity in the form of water (hydro Pumped Storage-turbine), again transformed into electricity through turbines during peak periods. But these storage capabilities are very limited.

An alternative to this method has been developed by the Austrian company Solar Fuel Technology (Salzburg), in cooperation with the Fraunhofer Institute for Wind Energy (IWES), Centre Research on solar energy and Hydrogen (ZSW) in Stuttgart and University of Linz: to store excess electricity produced by wind energy or photovoltaic as methane, synthetic neutral for the environment, gasometers and gas lines already exist. A demonstration plant is already operating successfully in Stuttgart. The first plant of 10 MW should be built by 2012.

The process involves converting the excess electricity produced in natural gas. The intermediate energy can be stored in chemical form in the natural gas network. The infrastructure for the reverse transformation of intermediate chemical energy is also operational: to burn natural gas and generating electricity in gas turbines or steam. The technology combines two processing methods of chemical energy into electricity, explains Michael Specht, a researcher at ZSW: the separation of water into hydrogen and oxygen using electricity (electrolysis) and transformation CO2 into methane (biogas) (methane is the main component of natural gas). Anaerobic digestion is itself a multi-step chemical process: CO2 is converted to methane (the final product) via the formic acid, formaldehyde and methanol. The main benefit of this technology lies in the possibility to use the existing natural gas network. Moreover, according to Michael Specht, conversion efficiency of electricity with natural gas exceeds 60%.

Local energy suppliers tanks and large centralized reservoirs are sized so they can cover the methane need for several months. The storage capacity of the natural gas network browsing is important and Germany amounted to 200 TWh – the consumption of several months. The grid has only 0.04 Wh. The integration infrastructure is easy, natural gas can be integrated into the supply system, pipelines and tanks, to fuel vehicles or light natural gas heaters.

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