Turning Electricity into Natural Gas

The Federal Government is setting ambitious targets for expanding renewable energy. In our series we present projects that promote the Energiewende (energy-system transformation) in a very practical way.

Storing electricity in the natural gas network may sound somewhat far-fetched, but is in fact an example of forward-looking technology. The idea is to eliminate fluctuations in the supply of wind and solar power.

Conventional power stations that burn gas and coal or use nuclear power provide a continuous supply of electricity and can be switched on or off as demand rises and falls. This is only possible to a limited extent with “green” power from hydroelectric, biomass and geothermal plants, however. Because the availability of wind and solar energy varies, a balancing system is needed to compensate when too much or too little energy is fed into the network.

Currently, two main technologies are used to “store” surplus electricity so that it is available when needed – the time-tested pumped storage power plants in low and high mountain ranges and, more recently, large accumulators in buildings for solar power generated on the roof. Neither will be sufficient to stabilize the electricity system in future, however. One possible solution here is the “power-to-gas” technology that is currently being trialled in around 20 pilot plants in Germany – for example in Stuttgart, Frankfurt am Main and Bad Hersfeld.

In a power-to-gas plant, surplus green energy is used to break down water by electrolysis into hydrogen and oxygen. The hydrogen is either stored in small proportions directly in the natural gas network or is first converted into methane. Methane is also a major component of normal natural gas. The German natural gas network is around 400,000 kilometres long. Later, the gas can then be used in power stations to generate electricity again.

As yet, the technology is in its infancy, and is still expensive. The main problem is that a relatively large amount of the energy is lost in the conversion process. Nonetheless, experts hope that “power-to-gas” will soon be ready for large-scale rollout. Recently, the world’s biggest research plant for the methane variant was opened in Stuttgart-Vaihingen. It is run by the Centre for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW).



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