“Green” hydrogen

"Green hydrogen" refers to hydrogen produced by water electrolysis using renewable electricity (wind, solar, hydroelectric, etc.), as opposed to "grey" hydrogen (natural gas reforming steam) or "blue" hydrogen (with CO₂ capture). In buildings and at the regional level, it's not a "hydrogen heater," but a useful energy carrier for storing surplus electricity, securing critical uses (backup, business continuity), and decarbonizing certain processes or fleets. Hydrogen becomes relevant when considering microgrids, neighborhoods, isolated sites, logistics parks, or heat/energy networks seeking long-term flexibility that batteries cannot adequately provide.

Green hydrogen: definition and scope of building/territory

Technically, green hydrogen is obtained via electrolyzers (PEM, alkaline, SOEC) powered by renewable energy sources, then stored (compressed gas, sometimes liquid or solid) and used by fuel cells to produce electricity and heat (cogeneration is possible). At the building scale, typical use cases are:

• Low-carbon electrical backup (heat pump + storage) for data rooms, healthcare, critical sites;
  
  
• Smoothing/storage of local RES (PV) when grid injection is constrained;
  
  
• Resilience-oriented CPE/BMS: covering a few hours/days of energy crisis;
  
  
• Site mobility (forklifts, hydrogen utility vehicles): pooling production and storage.
  At the territorial level, the focus is more on hydrogen hubs: shared production, renewable energy PPAs, guarantees of origin, distribution to captive fleets (buses, dump trucks), industrial parks, and even controlled injection into certain gas networks (blending). The benefit: creating an ecosystem where local renewable energy resources supply electricity and heat… but with delayed demand thanks to hydrogen storage.

Advantages, limitations and points to consider

Interests:

• Decarbonizing emergency services and certain mobility/logistics;
• Medium/long term storage is better suited than battery for durations > a few hours;
• Building/territory resilience (islanding, business continuity);
• Capitalizing on PV/wind peaks (avoiding load shedding), with possible cogeneration useful for DHW/AHU heating.

Boundaries :

• Overall Power-to-H₂-to-Power chain efficiency is modest (often 25–40% depending on the case): hydrogen is not a "plug-and-play" substitute for electricity;
• CAPEX/OPEX still high (electrolyzers, heat pumps, storage, maintenance) and demanding regulatory/safety framework (ventilation, detection, ATEX, installation);
• Firstly, territorial relevance: at the scale of a standard building, passive solutions + BMS + electric heat pumps + batteries often remain more efficient.

Points to consider:

• Hierarchy of solutions: sobriety/efficiency > direct RES > battery storage; H₂ intervenes if a long-term flexibility deficit remains.
• System integration (BMS, load curve, usage profiles), electricity quality (for electrolysis) and heat recovery (heat pump in cogeneration).
• Contractual framework: PPA, guarantees of origin, third-party investment schemes and service sharing (electricity, heat, mobility).

Anecdote — “Too much sun, not enough evening”

A business park by the sea had a generous solar array… which produced a good amount of energy when the offices were empty. Rather than installing an oversized battery, the park tested a shared mini hydrogen hub: during the day, surplus solar power fuels electrolysis; in the evening, a fuel cell provides backup power for several buildings and supplemental heat for the neighboring workshop. Bonus: the same station also fuels two forklifts in the warehouse. Moral of the story: when production and consumption never quite align, a little hydrogen can act as a mediator… with an hourglass instead of a plug.