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Renewable hydrogen from water electrolysis could contribute to the defossilization of various energy intensive sectors but continues to suffer from unfavorable economics. Attention is being paid to the direct supply of renewable electricity to electrolyzers; in particular from photovoltaic (PV) and wind units, whose fixed remuneration period has expired. However, detailed analysis of such operating strategies via modeling and simulation of the dynamic behavior of alkaline electrolysis (AEL) and polymer electrolyte membrane electrolysis (PEMEL) is lacking. In this work, an electrolyzer model is developed for both AEL and PEMEL and analyzed for PV and wind power input data sets from the region of northwest Germany. It is shown that key performance indicators (KPI) such as hydrogen production efficiency, electricity utilization rate, product output and net production costs are highly reliant on the shape of transient power input signals as well as the electrolyzers ability to cope with them. PEMEL technology generally has higher electricity utilization rates than AEL, while AEL still achieves relatively large hydrogen production quantities due to its higher efficiency. Thus, the better operational flexibility of PEMEL cannot generally be considered advantageous in terms of hydrogen production quantities – the same applies for economics. The most competitive hydrogen production costs were 4.33 € per kg for the AEL technology with direct electricity supply from old wind farms, which no longer receive fixed remuneration. • Modeling and simulation of dynamic electrolyzer operation over a period of one year. • KPI's are reliant on transient power profile and electrolyzer operating flexibility. • Cheapest hydrogen production costs are 4.33 €/kg for AEL with onshore wind. [ABSTRACT FROM AUTHOR]

PEM (Polymer Electrolyte Membrane) fuel cells have the potential to reduce our energy use, pollutant emissions, and dependence on fossil fuels. In the past decade, significant advances have been achieved for commercializing the technology. For example, several PEM fuel cell buses are currently rated at the technical readiness stage of full-scale validation in realistic driving environments and have met or closely met the ultimate 25,000-h target set by the U.S. Department of Energy. So far, Toyota has sold more than 4000 Mirai PEM fuel cell vehicles (FCVs). Over 30 hydrogen gas stations are being operated throughout the U.S. and over 60 in Germany. In this review, we cover the material, design, fundamental, and manufacturing aspects of PEM fuel cells with a focus on the portable, automobile, airplane, and space applications that require careful consideration in system design and materials. The technological status and challenges faced by PEM fuel cells toward their commercialization in these applications are described and explained. Fundamental issues that are key to fuel cell design, operational control, and material development, such as water and thermal management, dynamic operation, cold start, channel two-phase flow, and low-humidity operation, are discussed. Fuels and fuel tanks pertinent to PEM fuel cells are briefly evaluated. The objective of this review is three fold: (1) to present the latest status of PEM fuel cell technology development and applications in the portable and transportation power through an overview of the state of the art and most recent technological advances; (2) to describe materials and water/thermal transport management for fuel cell design and operational control; and (3) to outline major challenges in the technology development and the needs for fundamental research for the near future and prior to fuel cell world-wide deployment. [ABSTRACT FROM AUTHOR]