Development of a Modular Direct Current System for Decentralized Hydrogen Production from Renewable Energies

In the "mDC2H2" project, we have developed a modular, efficient direct-current system for integrating PEM electrolyzers for decentralized hydrogen production. The focus was on developing a highly efficient DC/DC converter for the voltage adaptation between the DC bus and the electrolyzer. By employing a lossless resonant circuit topology and state-of-the-art SiC semiconductors, we were able to significantly reduce the system costs.

Initial Situation

With the amendment to the Climate Protection Act, the federal government tightened the climate protection targets and anchored the goal of greenhouse gas neutrality by 2045. By 2030, emissions are to fall by 65 percent compared to 1990. In June 2020, the national hydrogen strategy of the federal government was adopted, according to which by 2030 Germany should have hydrogen production plants with a total capacity of up to 5 GW. The economic production of hydrogen imposes various technical and economic requirements on the electrolyzer of a Power-to-Gas installation.

Direct-current-based energy systems have advantages for integrating photovoltaic, battery, and electrolyzer systems; modular DC/DC converters enable efficient decentralized hydrogen production.

Objective

The project’s aim, in addition to developing the DC/DC converter, was to explore DC networks, which are becoming increasingly important in industry. We also gained insights into the interaction between electrolyzers and batteries.

Approach

As part of the project, in collaboration with the industrial partner Handtmann, we developed an efficient modular direct-current system for integrating PEM electrolyzers. Hydrogen production from renewable energies on-site as well as from the grid is possible with the highly efficient DC technology and was evaluated with a technology demonstrator. The DC infrastructure enables the integration of various components, such as PV systems, batteries, and even an electrolyzer as a hybrid storage system. An intelligent operating-management system enables the optimal coordination of local feed-in/storage.

Results

The developed system consists of modular, scalable power-electronic converters in a plug-and-play principle, each with a rated power of 30 kW per rack. The innovation of the system architecture arises from the reduced system costs and the high efficiency of the hybrid PEM-battery storage:

• Modular overall system with decoupling of the AC and DC sides (scalability of converter power over the DC bus, adaptation to power class and partial-load operation of the energy generators, minimization of grid feedback)
• Increase in power density and efficiency through the use of new power semiconductors (SiC), higher switching frequencies, and innovative technologies (soft-switching topologies)
• Lifetime extension of PEM electrolyzer stacks (modularity in 100-kW units and high quality of the power supply)
• Increase in the electrolyzer’s utilization hours by integrating additional DC-bus participants (e.g., bidirectional DC industrial devices) or by absorbing surplus capacity from the grid
• Integration of the converters into existing DC infrastructure (PV, e-mobility, battery storage, industrial grids)
• DC-bus management and higher-level operations management with intelligent energy management

The "mDC2H2" research project was funded by Invest BW on behalf of the Baden-Württemberg Ministry of Economic Affairs, Labour and Tourism and supported by VDE/VDI/IT. In addition to the Fraunhofer Institute for Solar Energy Systems ISE, Handtmann e-solutions GmbH & Co. KG acted as project coordinator.