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Conceived by a Dutch research group, the proposed system aims to store surplus renewable electricity through hydrogen generation and battery storage, with the latter being used only when hydrogen generation is not immediately available. Despite its high initial cost, the system can offer stable operation.
Researchers at the Hanze University of Applied Sciences in Groningen, the Netherlands, have for the first time studied how to combine hydrogen production and battery storage with rooftop photovoltaics or small wind turbines in off-grid homes. “To our knowledge, no published study has used the hydrogen system as primary storage when hybridizing renewables with batteries and, more importantly, no study has taken into account the variable startup requirements of hydrogen membrane electrolyzers. proton exchange (PEM) for hydrogen production and storage when designing off-grid renewable energy systems,” the group stated, adding that the batteries are designed to avoid cuts when hydrogen production cannot be prioritized.
The scientists explained that hydrogen systems based on PEM electrolysis offer the advantage of being fast response systems, suitable for storage systems in which the hydrogen system acts as the primary storage unit coupled to a battery as secondary storage. However, they also stressed that hydrogen generated through electrolysis must be dried and purified of traces of water and oxygen before it can be used.
The proposed system is intended to store excess solar energy, with the battery acting as a primary storage unit only when hydrogen generation is not immediately available. It consists of a 4.5 kW PEM hydrogen electrolysis system, a 0.85 m3 hydrogen storage tank, a 0.8 kW purification unit, a PEM hydrogen fuel cell and a hydrogen ion battery. lithium. “The fuel cell can only supply energy directly to the consumer and does not charge the battery or support the electrolyzer,” the academics explain. “The electrolyzer and the fuel cell need demineralized water and air to operate, respectively.”
The system also relies on a pressure control valve to set the hydrogen outlet pressure, which can be adjusted to almost 50 bar without external means. It is also capable of keeping the electrolyzer running when the surplus solar energy is close enough to the minimum power of the electrolyzer and the expected surplus energy in the next 10 minutes is relatively high. “It uses the battery to store energy when the power or duration of the power of the renewables is insufficient for the electrolyzer system to start and operate,” the scientists explain.
The research group simulated the operation of the system using Python software and used multiple inputs to decide how to store electrical energy when there is a surplus. They assumed that the system would be deployed in a typical Dutch single-family house with an annual demand of 4 MWh.
The simulation showed that the best system configuration for the PV source includes a 2.65 kW solar field with a tilt angle of 35 degrees and an azimuthal angle of 180 degrees. The cost of the photovoltaic system was assumed to be 1,317 euros ($1,430)/kW, while that of the electrolyzer and fuel cell was estimated at 9,677 euros and 7,500 euros, respectively. The cost of the hydrogen tank was indicated at 1,915 euros and that of the 2.93 kW battery was assumed at 372.5 euros/kWh.
The analysis showed that, in no case, the electrolyzer could operate at its maximum nominal power, which means that its size can be reduced, thus reducing system costs, the researchers emphasize. “The sensitivity analysis on the variation of the nominal power of the electrolyzer demonstrated that an electrolyzer with a nominal power between 1,550 W and 2,000 W is more suitable and profitable for the base case configuration defined in this study,” they further explained, adding that the optimal battery capacity was identified around 3 kW.
The series of simulations also showed that relying solely on wind power was more cost-effective than using solar power alone, while a combination of both sources offered the best results. “The energy required by the purification unit can be considered negligible for all scenarios,” the academics added, noting that future research should test the proposed solution on a larger scale or in a system that integrates heat production.
The system was presented in the study “ Simulation and analysis of hybrid hydrogen-battery renewable energy storage for off-electric-grid Dutch household system ” the electrical grid), published in the International Journal of Hydrogen Energy . |
