Tapping into Previously Unused Green Electricity

Electrolysis can react to fluctuations in the supply generated by renewable energy in a matter of milliseconds – much faster than previous methods. The prototype of a storage facility equipped with PEM technology produces between two and six kilograms of hydrogen per hour.

One such facility, which is rated at 0.3 megawatts at peak capacity, went into operation at the Coal Innovation Centre at the RWE power plant in Nieder­außem as part of the CO2RRECT (CO2‑Reaction using Regenerative Energies and Catalytic Technologies) project.

It will simulate operational situations resulting from conditions that could be caused by fluctuations in the amount of electricity fed into the grid. Siemens and its partners in the project, including RWE, Bayer, and ten academic institutions, aim to use electrolytically harvested hydrogen to convert carbon dioxide into a raw material that can be used in the industrial production of chemicals.

Energy storage facilities for electricity from renewable sources are important components of the energy transition. Compressed hydrogen gas has a high energy density and could be stored in underground salt caverns, for example. When desired, the hydrogen can be converted to electricity, and it can also be used as a fuel and as a raw material for industry. Until now, electrolysis facilities were not conceived or designed to be able to react flexibly to large energy fluctuations.

At Siemens' Industry Sector a new low-maintenance electrolysis technology has been developed based on research from Corporate Technology. In the electrolyzer a proton exchange membrane (PEM) separates the electrodes on which hydrogen and oxygen form. One reason this electrolyzer can react so quickly is that the membrane is very stable in response to pressure differences in the two gas chambers. Because it is equipped with internal cooling and is designed for high current densities, it can easily handle three times its rated capacity for some time and needs almost no electricity at all when in standby mode.

Smaller versions of this system could soon be installed at filling stations to produce hydrogen for fuel cell vehicles. Modular systems with outputs of up to ten megawatts should be available in a few years. These would be appropriate for industrial and other applications.

In the long term, systems using PEM electrolysis should be able to operate in the triple-digit megawatt range that would be necessary to handle the output of offshore wind farms and/or provide load balancing capacity for primary and secondary control reserves. Siemens will continue to develop the design, materials, and manufacturing processes for PEM electrolysis.