Potential of Membrane Alkaline Water Electrolysis in Connection with Renewable Power Sources

Hydrogen is an efficient energy carrier with numerous applications in various areas as industry, energetics, and transport. Its potential depends also on the origin of the energy used to produce the hydrogen with respect to its environmental impact. Where the standard production of hydrogen from fossil fuels (methane steam reforming, etc.) doesn’t bring any benefit to decarbonisation of society. The most ecological approach involves water electrolysis using ‘green’ electricity, such as renewable power sources. Such hydrogen thus stores energy which can be used later. Hydrogen, used in the transport sector, can minimize its environmental impact together with preserving the driving range and decrease the recharge/refill time in comparison with a pure battery-powered vehicle. For transportation the hydrogen filling stations network is required. Local production of hydrogen is one of proposed scenarios. The combination of electrolyser and renewable power source is the most viable local source of hydrogen. It is important to know the possible amount of hydrogen produced with respect to local environmental and economic conditions. Hydrogen production by water electrolysis is an extensively studied topic. Among the three most prominent types, which are the alkaline water electrolysis (AWE), proton-exchange membrane (PEM) electrolysis and high-temperature solid-oxide electrolysis, AWE is the technology which is widely used in the industry for the longest time. In the recent development, AWE is being modified by incorporation of anion-selective membranes (ASMs) to replace the diaphragm used as the cell separator. In comparison with the diaphragm, ASMs perform acceptably in environment with lower temperatures and lower concentrations of the liquid electrolyte, thus, allowing for very flexible operation similarly to the PEM electrolysers. On the other hand, ASMs are not yet in a development level where they could outperform the diaphragm and PEM in long-term stability. Renewable sources of energy, predominantly photovoltaic (PV) plants and wind turbines, operate with non-stable output of electricity. Considering their proposed connection to the water electrolysis, flexibility of such electrolyser is of the essence for maximizing hydrogen production. The aim of this work is to consider a connection of a PV plant with an AWE. Power output data from a real PV plant are taken as a source of electricity for a model AWE. The input data for the electrolyser were taken from a laboratory AWE. The AWE data were measured using a single-cell electrolyser using Zirfon Perl® cell separator with nickel-foam electrodes. Operation including ion-selective membranes was also taken into consideration. Data from literature were used to set possible operation range and other electrolyser parameters. Small-scale operation was then upscaled to match dimensions of a real AWE operation. Using the before mentioned data, a hydrogen production model was made. The model takes the power output of the PV plant in time and decides whether to use the power for preheating of the electrolyser or for electrolytic hydrogen production. Temperature of the electrolyser is influenced by the preheating, thermal-energy loss of the electrolytic reactions, or cooling to maintain optimal conditions. The advantage of the created model is its variability for both energy output of the power plant or other instable power source and the properties of the electrolyser. It can be used to predict hydrogen production in time with respect to the electrolyser and PV power plant size. The difference between standard AWE and AWE with ion exchange membrane is mainly shown during start-up time where membrane based electrolyser shows better efficiency. Frequency of start-stop operation modes thus influences the choice of suitable electrolyser type. Another output is to optimize design of an electrolyser to fit the scale of an existing plant from economical point of view. This knowledge is an important input into the plan which is set to introduce hydrogen-powered transport options where fossil-fuel powered vehicles is often the only option, such as unelectrified low-traffic railroad networks. Acknowledgment: This project is financed by the Technology Agency of the Czech Republic under grant TO01000324, in the frame of the KAPPA programme, with funding from EEA Grants and Norway Grants.