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The penetration of renewable energy sources (RES) has caused some challenges for grid operation, including frequency variation, low power quality, and reliability issues. These challenges can be mitigated with the help of battery energy storage systems (BESS) which are characterized by long lifetime and high-power capability. Among the different types of high-power storage devices, lithium titanate oxide (LTO) batteries and lithium-ion capacitor (LIC) cells attract more attention. The performance behavior, the total cost of the battery system, and the system's size are some other criteria for cell selection. This research compares the performance behavior of an LTO battery type for this application with two LIC type storage system at positive and negative temperatures and also considers the system size, cost, and lifetime of the BESS. The result proves that LICs are better candidates for low and high temperature applications in terms of energy efficiency and capacity drop. However, in terms of cost and size, the highenergy LTO cells are a better selection.

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Instead of storing the energy produced by photovoltaic panels in batteries for later use to power electric loads, green hydrogen can also be produced and used in transportation, heating, and as a natural gas alternative. Green hydrogen is produced in a process called electrolysis. Generally, the electrolyser can generate hydrogen from a fluctuating power supply such as renewables. However, due to the startup time of the electrolyser and electrolyser degradation accelerated by multiple shutdowns, an idle mode is required. When in idle mode, the electrolyser uses 10% of the rated electrolyser load. An energy management system (EMS) shall be applied, where a storage technology such as a lithium-ion capacitor or lithium-ion battery is used. This paper uses a state-machine EMS of PV microgrid for green hydrogen production and energy storage to manage the hydrogen production during the morning from solar power and in the night using the stored energy in the energy storage, which is sized for different scenarios using a lithium-ion capacitor and lithium-ion battery. The mission profile and life expectancy of the lithium-ion capacitor and lithium-ion battery are evaluated considering the system’s local irradiance and temperature conditions in the Australian climate. A tradeoff between storage size and cutoffs of hydrogen production as variables of the cost function is evaluated for different scenarios. The lithium-ion capacitor and lithium-ion battery are compared for each tested scenario for an optimum lifetime. It was found that a lithium-ion battery on average is 140% oversized compared to a lithium-ion capacitor, but a lithium-ion capacitor has a smaller remaining capacity of 80.2% after ten years of operation due to its higher calendar aging, while LiB has 86%. It was also noticed that LiB is more affected by cycling aging while LiC is affected by calendar aging. However, the average internal resistance after 10 years for the lithium-ion capacitor is 264% of the initial internal resistance, while for lithium-ion battery is 346%, making lithium-ion capacitor a better candidate for energy storage if it is used for grid regulation, as it requires maintaining a lower internal resistance over the lifetime of the storage.