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When we think about hydrogen and the future “H2 economy”, we tend to think about the production of H2 for use as a fuel in a fuel-cell based transportation system.  However, there are many opportunities for H2 use beyond transportation, including grid-scale energy storage.

One concept that has received increasing attention in recent years is that of “power-to-gas”, the idea of converting excess electricity into H2 through water electrolysis. Power-to-gas could play an important role in grid-scale energy storage thanks to its ability to quickly absorb large amounts of excess electricity produced by intermittent renewable resources such as solar or wind.

In Germany, which currently gets a higher percentage of its electricity from solar and wind than any other country, the government has initiated 20 power-to-gas demonstration projects:

http://www.technologyreview.com/news/530331/germany-and-canada-are-building-water-splitters-to-store-renewable-energy/

Many of these projects will be based on polymer electrolyte membrane (PEM) electrolyzers, which use electricity to electrochemically split water into H2 and O2 at very high current densities, typically 2-4 A/cm2. A leading company in the application of PEM electrolyzer-based systems for power-to-gas is Hydrogenics, a Canadian company.

After being produced, the H2 from power-to-gas plants must be stored until electricity prices go back up. Presently, many demonstrations seek to leverage the existing natural gas infrastructure for this purpose.  This can be achieved by reacting H2 with with CO2 in a methanation reactor for direct production of CH4, or, as is being done in a number of the German demonstration projects, the H2 can be input directly into the current natural gas piping infrastructure.   H2 is compatible with CH4 at low percentages, and can therefore be stored in the existing infrastructure at minimal cost, and the mixture can then be burned in a natural gas power plant to be converted back into electricity.

For a full list of power-to-gas pilot plants for stationary applications, see this article:

http://www.sciencedirect.com.ezproxy.cul.columbia.edu/science/article/pii/S0360319912026481#

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