A group of researchers at Qatar's Hamad Bin Khalida University is proposing a new concept for standalone EV recharging stations, based on the hybridization of multiple renewable energy sources and different types of storage.
The system, which is designed to ensure uninterruptable charging operation during night times, cloudy days, and low wind speeds and to fast-charge 80 electrical vehicles daily, is powered by a combination of concentrated photovoltaics and thermal solar (CPV/T), wind energy, and biomass combustion technologies, and incorporates storage technologies based on lithium-ion, hydrogen, ammonia and phase change material (PCM).
The charging station also embeds a lithium bromide Li–Br absorption cooling system, which is used for the cooling of lithium-ion batteries and liquefying the generated gaseous ammonia for safer storage purposes.
The electricity produced by the CPV/T unit is used for hydrogen production, EV charging, ammonia production and battery storage in a consecutive manner. “If sufficient electricity is produced from CPV/T in a day, all the mentioned processes may be supplied with electricity from this subsystem,” the researchers explained. “Otherwise, the first-in-order processes will be supplied until all the produced electricity from CPV/T is consumed and the other energy sources shall take over to supply the deficit.” The thermal energy generated by the CPV/T device is used for charging PCM in the thermal storage unit and supplying the cooling system.
Wind power is used for EV and battery charging subsequently, while the biomass system is utilized to complement the other sources during night times and unfavorable weather conditions.
The scientists conducted an analysis of the performance of the whole system, as well as of the energy efficiencies of the subsystems and main components, and found that its overall energy efficiency is 45% and the exergy efficiency is 19%, which they said are in the higher range compared with similar multi-generation systems in the existing literature. Exergy efficiency computes the effectiveness of a system relative to its performance in reversible conditions while energy efficiency computes how much energy is produced in a process versus the amount of energy given. “The CVP/T thermal efficiency and electrical exergy efficiency are found to be 45% and 37%, respectively,” the academics specified. “The energy efficiencies of hydrogen and ammonia fuel cells are found to be 77% and 72%, respectively.”
The research team aims now to improve the overall efficiency of the system by re-utilizing the heat loss generated from CPV/T for external applications, increasing the CPV/T water flow rate, and creating hourly scheduling to balance supply and demand. ”
The system is described in the paper Development of an off-grid electrical vehicle charging station hybridized with renewables including battery cooling system and multiple energy storage units, published in Energy Reports.
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