Alkaline Water Electrolysis Powered by Renewable Energy: A Review

Abstract

Alkaline water electrolysis is a key technology for large-scale hydrogen production powered by renewable energy. As conventional electrolyzers are designed for operation at fixed process conditions, the implementation of fluctuating and highly intermittent renewable energy is challenging. This contribution shows the recent state of system descriptions for alkaline water electrolysis and renewable energies, such as solar and wind power. Each component of a hydrogen energy system needs to be optimized to increase the operation time and system efficiency. Only in this way can hydrogen produced by electrolysis processes be competitive with the conventional path based on fossil energy sources. Conventional alkaline water electrolyzers show a limited part-load range due to an increased gas impurity at low power availability. As explosive mixtures of hydrogen and oxygen must be prevented, a safety shutdown is performed when reaching specific gas contamination. Furthermore, the cell voltage should be optimized to maintain a high efficiency. While photovoltaic panels can be directly coupled to alkaline water electrolyzers, wind turbines require suitable converters with additional losses. By combining alkaline water electrolysis with hydrogen storage tanks and fuel cells, power grid stabilization can be performed. As a consequence, the conventional spinning reserve can be reduced, which additionally lowers the carbon dioxide emissions.

Modeling the Dynamic Power‐to‐Gas Process: Coupling Electrolysis with CO2 Methanation

“…Various approaches with different complexity can describe the system behavior of alkaline water electrolyzers. While physically reasonable models are setup-independent since system dimensions can be defined by the required input parameters, empirical correlations are only valid for the actual electrolyzer system [2]. Often, the parameters for physically reasonable models are challenging to quantify and the development of such models is a recent research topic [7].…”

“…A trend for PtG is the development of small-scale container-based units for decentralized energy storage applications. These units usually consist of an alkaline water electrolyzer (AEL) for the production of H 2 owing to low investment and maintenance costs as well as a high lifetime [2]. Due to the limited space, an intensified reactor is required in terms of heat and mass transfer, e.g., a microstructured reactor.…”

Faraday’s Efficiency Modeling of a Proton Exchange Membrane Electrolyzer Based on Experimental Data

“…This model has been obtained from experiments performed on a PHOEBUS electrolyzer (26 kW, 7 bar, T = 40 • C, 0.25 m 2 , 21 cells) [10]. The Faraday's efficiency given by Equation (9) has been plotted according to the current density in Figure 3. This model has been obtained from experiments performed on a PHOEBUS electrolyzer (26 kW, 7 bar, T = 40 °C, 0.25 m 2 , 21 cells) [10].…”

“…This model has been obtained from experiments performed on a PHOEBUS electrolyzer (26 kW, 7 bar, T = 40 °C, 0.25 m 2 , 21 cells) [10]. The Faraday's efficiency given by Equation (9) has been plotted according to the current density in Figure 3.…”

“…The partial load range is an important issue when coupling electrolyzers with renewable energy sources to ensure decarbonized hydrogen production. Since renewable energy sources are very dynamic sources, the electrolyzers must be able to absorb the energy during dynamic operation and even at low wind speed [9]. However, the limited partial load range and low current densities of alkaline electrolyzers make them less efficient during dynamic operation.…”