Hybrid hydrogen-battery system for off-grid PV-powered homes

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

“To the best of our knowledge, no published study used the hydrogen system as the main storage when hybridizing renewable energies with batteries and, most importantly, no studies have considered the variable start-up requirements for proton exchange membrane (PEM) electrolyzers for hydrogen production and storage when designing off-grid renewable energy systems,” the group stated, adding that the batteries are intended to be used to avoid curtailment 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 where the hydrogen system acts as the main storage unit coupled with a battery as secondary storage. They also stressed, however, that the hydrogen generated via electrolysis needs to be dried and purified from traces of water and oxygen before it can be used.

The proposed system is intended for storing surplus solar power, 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 lithium-ion battery. “The fuel cell can only supply power directly to the consumer and it does not charge the battery nor support the electrolyzer,” the academics explained. “The electrolyzer and fuel cell require demineralized water and air for operation, respectively.”

The system also relies on a pressure control valve to set the output pressure of the hydrogen, which can be set to almost 50 bar without external means. It is also able to maintain the electrolyzer running when surplus solar power is close enough to the electrolyzer’s minimum power and the expected surplus power in the following 10 minutes is relatively high. “It uses the battery to store energy when the power or the duration of the power from renewables is insufficient for the electrolyzer system to start up and operate,” the scientists said.