Surplus renewable power (solar/wind generation that would otherwise be curtailed) can be split between two storage paths. The electrolyzer uses electricity to split water into hydrogen and oxygen (H₂O → H₂ + ½O₂), storing the hydrogen in a compressed tank; later a fuel cell recombines that hydrogen with oxygen to regenerate electricity. The battery stores the same surplus electrochemically and returns it directly.
- Round-trip efficiency = electricity out ÷ electricity in, measured live from the moment you last reset the stats.
- Hydrogen path loses energy twice — once making H₂ (~70% efficient), once converting it back (~50% efficient) — for a combined ~30-45%.
- Battery path loses energy once, in resistive/chemical losses, for ~85-95% round trip — but a real lithium battery also bleeds a small amount of charge every hour just sitting there (modeled here), which the hydrogen tank essentially does not.
That is why grids favor batteries for daily solar/demand cycling, but reach for hydrogen (or other long-duration media) to bridge weeks or seasons — e.g. storing summer solar surplus to burn in winter.