The possibility to save the surplus of green electricity efficiently and independently of location by transforming it into methane gas and storing it in the natural gas network can be very important to guarantee a more effective use of renewable technologies.

At the end of June a new power-to-gas plant, probably the biggest worldwide, was inaugurated in Werlte (Germany) .
The plant uses green electricity from a neighboring biogas production plant, water and carbon dioxide to produce hydrogen by electrolysis and then synthetic methane, called e-gas. The hydrogen could be used directly to power fuel-cell vehicles, but for the time being, in the absence of widespread use of hydrogen cars and of an area-wide infrastructure, methanation is carried out as a second step. Hydrogen is reacted with CO2 (once again coming from the biogas plant) to produce synthetic methane, that can be easily used in cars or fed into the national natural gas distribution system. The waste heat resulting from methanation is used as process energy in the adjacent biogas plant, significantly increasing the overall efficiency.

The plant was built by the German automobile manufacturer Audi in collaboration with ETOGAS GmbH and its project partner MT-BioMethan GmbH, and should start working at full capacity in fall 2013. It is expected to produce about 1,000 metric tons of methane per year, chemically binding some 2,800 metric tons of CO2 . This roughly corresponds to the amount that a forest of over 220,000 beech trees absorbs in one year. Water and oxygen are the only by-products.

The project aims to provide the company customers with certified green fuel, since they can order a quota of e-gas when they purchase their car. However, the benefits of a project like this can extend also outside the automobile industry: since Germany is a major producer of electricity from non-programmable renewable sources, many German energy utilities are working on the idea of power-to-gas cogeneration as well, and following with projects of their own.

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