Hybrid hydrogen battery system for off-grid photovoltaic homes – pv India magazine

May 24, 2024 Emiliano Bellini

Researchers at the Hanze University of Applied Sciences in Groningen, the Netherlands, have explored for the first time how to combine hydrogen production and battery storage with rooftop photovoltaic power or small wind turbines in off-grid households.

“To the best of our knowledge, no published study has used a hydrogen system as primary storage when hybridizing renewable energies with batteries and, most importantly, no study has considered the variable start-up requirements of proton exchange membrane (PEM) electrolysers for hydrogen production and storage designing off-grid renewable energy systems,” the group said, adding that batteries are intended to be used to avoid constraints when hydrogen production cannot be prioritized.

The researchers explained that hydrogen systems based on PEM electrolysis have the advantage of being fast-response systems, suitable for storage systems in which the hydrogen plant acts as primary storage combined with a battery as secondary storage. However, they also stressed that hydrogen produced by electrolysis must be dried and cleaned of traces of water and oxygen before it can be used.

The proposed system is designed to store surplus solar energy, with the battery acting as primary storage only when immediate hydrogen production is not 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 lithium-ion battery. ” fuel cell it can only supply energy directly to the consumer and does not charge the battery or support the electrolyzer,” the researchers explained. “The electrolyzer and fuel cell require demineralized water and air, respectively, to operate.”

The system also uses a pressure control valve to set the hydrogen output pressure, which can be set to almost 50 bar without the use of external means. It is also able to keep the electrolyzer running when the solar surplus is close enough to the minimum electrolyzer power and the expected surplus power in the next 10 minutes is relatively high. “It uses a battery to store energy when the power or duration of renewable power is insufficient for the electrolyzer system to start and operate,” the researchers say.

The research group simulated the system’s performance using Python software and, based on multiple inputs, decided how to store electricity in the event of a surplus. They assumed that the system would be implemented in a typical Dutch single-family house, whose annual demand is 4 MWh.

The simulation showed that the best system configuration for the photovoltaic source is a 2.65 kW photovoltaic array with a tilt angle of 35 degrees and an azimuth angle of 180 degrees. The cost of the photovoltaic system was assumed to be EUR 1,317 ($1,430)/kW, while the cost of the electrolyzer and fuel cell was estimated at EUR 9,677 and EUR 7,500, respectively. The cost of the hydrogen tank was estimated at EUR 1,915 and the cost of the 2.93 kW battery at EUR 372.5/kWh.

The analysis showed that the electrolyzer was by no means able to operate at its maximum nominal power, which means it can be reduced, thereby reducing system costs, the researchers stressed. “A sensitivity analysis on changing the nominal power of the electrolyzer showed that an electrolyzer with a nominal power of 1,550 W to 2,000 W is more suitable and cost-effective for the base case configuration defined in this study,” they further explained, adding that the optimal battery capacity was set at level of approximately 3 kW.

A series of simulations also showed that using only wind power was more cost-effective than using only solar power, with a combination of the two providing the best results. “The energy required by the purification unit can be considered negligible in all scenarios,” the researchers added, noting that future research should test the proposed solution on a larger scale or in a system integrating heat production.

The system was introduced in the study ““Simulation and analysis of hybrid renewable energy storage using hydrogen batteries for a Dutch off-grid home system”, published in: International Journal of Hydrogen Energy.