A stable energy supply in the future can only be ensured with the storage of energy on a large scale. On the basis of the liquid organic hydrogen carrier system (LOHC) and with the aid of PEM electrolysis and solid oxide fuel cells, the dimensions and above all the capacity of a storage power plant to replace…

… a conventional power plant will be determined using the example of a lignite-fired power plant. If this is applied to all lignite-fired power plants in Germany, the potential of using surplus electricity from hydrogen becomes apparent.

In order to enable the energy turnaround to progress, energy produced by wind and sun must be able to be stored over longer periods of time in the terawatt hour range. By 2022, when the nuclear phase-out will also take place, 30 percent of the coal capacity is to be shut down. Electricity is already being produced in excess of demand and is currently largely regulated, i.e. not used. The large-scale storage of energy in the form of hydrogen is of great importance for the temporal compensation of fluctuations in electricity production and for meeting the electricity demand during a dark lull.

How could electricity supply be guaranteed when coal-fired power is phased out, so that the energy turnaround can be implemented? How, for example, could H2 be used to replace a lignite-fired power plant? What storage capacities are required?

Surplus electricity for H₂ generation

With the help of the literature, it can be determined that large-scale storage system such as pumped storage power plants and compressed air storage power plants have little expansion potential, so that energy can only be stored on a large scale with H₂. Above all, surplus electricity should be stored using this. In the currently used electricity system, which is not very flexible, surplus electricity is generated not only by weather-dependent renewable energies, but also by must-run power plants, most of which are operated conventionally. If too much electricity is generated, solar and wind power plants are switched off, power plants are shut down or ramped up, or electricity is exported. Much energy is lost from year to year in increasing measure unused, although this energy could be used for hydrogen, which is produced by electrolysis.

PEM electrolysis with high efficiencies of up to 74 % is best suited for the conversion of fluctuating power generation [1]. Fuel cells can then, if required, re-introduce the energy stored in chemical form. The solid oxide fuel cell appears to be the most suitable for continuous power delivery in terms of current efficiency at 50 to 65 % and the possibility of using the waste heat. In turn, the PEM fuel cell would be preferred for the provision of control power due to its flexibility in load changes and short start-up times.

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read more in H2-international October 2019

Authors:
Sabrina Schiefelbein
Prof. Klaus-Michael Ahrend, Hochschule Darmstadt, and board member, HEAG
Prof. Johannes Windeln, Wilhelm Büchner Hochschule‎