(417b) Dynamic Modeling and Control of a PEM Electrolyzer for Solar Photovoltaic Power Smoothing

The variability and intermittency of solar photovoltaic (PV) electricity under increasing renewable penetration can lead to frequent and steep ramping operations of conventional fossil fuel power plants. Hydrogen production via water electrolysis can serve as a controllable load and provide both short and long duration energy storage to reduce grid fluctuations and improve the resiliency of the grid system. The high efficiency and quick dynamic response of a polymer electrolyte membrane (PEM) electrolyzer can be used to both generate hydrogen and serve as a controllable load [1,2]. The capacity factors of both PV field and PEM electrolyzer can affect the performance of PV smoothing on the cloudy day. The generated green hydrogen must be stored under high pressure for subsequent utilizations (e.g., hydrogen fuel cell electric vehicle refueling). PEM electrolyzers directly producing high pressure hydrogen are more energy efficient than ambient electrolyzers followed by mechanical compression, but higher pressure leads to more undesired hydrogen permeation back to the oxygen side, which can cause lower hydrogen production efficiency, cell degradation, and safety risk of hydrogen explosion limit [3,4]. Electrolyzer operational pressure optimization under fluctuating electricity (i.e. current density) is developed for an integrated hydrogen system (renewable solar with green hydrogen production and storage). Different PV smoothing scenarios and varied pressure operation conditions of the PEM electrolyzer are investigated.

A high-fidelity dynamic model of a PEM electrolyzer cell/stack is developed with consideration of one-dimensional ("through-plane") mass/heat transfer coupled with electrochemical kinetics. The electrochemical reactions are modeled using Butler-Volmer kinetics with varying surface molar concentrations of components. Maxwell-Stefan diffusion equation is used to calculate the gas-phase species molar concentration in the backing and catalyst layers. Hydrogen permeation through membrane by diffusion and convective transport as a function of operational pressure is assessed. To evaluate the transient response of the PEM electrolyzer stack, real-time PV data based on a solar farm from Orlando Utilities Commission (OUC) is smoothed by the electrolyzer using a power signal control algorithm. The developed PV smoothing control algorithm and the electrochemical dynamic stack model show the effectiveness of an electrolyzer in smoothing the PV signal to increase the grid stability and flexibility.

[1] Kumar, S.S. and Himabindu, V., 2019. Hydrogen production by PEM water electrolysis–A review. Materials Science for Energy Technologies, 2(3), pp.442-454.

[2] Götz, M., Lefebvre, J., Mörs, F., Koch, A.M., Graf, F., Bajohr, S., Reimert, R. and Kolb, T., 2016. Renewable Power-to-Gas: A technological and economic review. Renewable energy, 85, pp.1371-1390.

[3] Trinke, P., Bensmann, B., Reichstein, S., Hanke-Rauschenbach, R. and Sundmacher, K., 2016. Hydrogen permeation in PEM electrolyzer cells operated at asymmetric pressure conditions. Journal of The Electrochemical Society, 163(11), p.F3164.

[4] Scheepers, F., Stähler, M., Stähler, A., Rauls, E., Müller, M., Carmo, M. and Lehnert, W., 2020. Improving the efficiency of PEM electrolyzers through membrane-specific pressure optimization. Energies, 13(3), p.612.