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Water electrolysis will be used to produce renewable hydrogen for energy storage and Power-to-X applications in the future renewable-energy-based energy systems. Therefore, the energy efficiency of hydrogen production will probably become a major issue. In this study, the effect of practical supply power converters on the specific energy consumption of MW-scale alkaline electrolyzers is studied and compared with an ideal DC power supply. The current quality and the stack specific energy consumption are studied in the case of traditional thyristor rectifiers and a transistor-based converter. The stack specific energy consumption is analyzed based on the simulated current waveforms and the electrical equivalent circuit of the electrolyzer stack. It is found that the transistor-based converter offers up to 14% lower electrolyzer stack specific energy consumption than the 6-pulse thyristor rectifier and up to 9.2% lower electrolyzer stack specific energy consumption than the 12-pulse thyristor rectifier as the current varies between 5000 A and 1000 A. The simulated change in the stack specific energy consumption of the MW-scale alkaline water electrolyzer outweighs the losses occurring in the rectifiers. Further, selection of the AC voltage level may have a more adverse effect on the stack specific energy consumption with the thyristor rectifier topologies compared with the transistor-based topologies.

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This paper proposes an extension for feasibility assessment of residential energy (heat and electricity) supply solutions in an operational environment undergoing major changes. In order to improve the life cycle economy of the energy supply, the design has to accommodate technological, economic, and regulatory changes in operational environment over the long time. New elements must be included in feasibility assessments of energy supply to ensure consideration of future economic opportunities and risks. The extended feasibility assessment brings up the profitability of “future proofed” more sustainable solutions with lower risks related to utilization costs and with improved resale value preservation. The findings of systematic literature study were structured and clarified into a decision support matrix to guide the assessment process. The procedure was verified by identifying the optimal energy supply solution for a net-zero energy single-family house in Southern Finland. The verification demonstrated that the procedure provides new insights on the economy and the climate implications of the energy solutions.

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