The Mini LED sign is a neat compact 24VDC backlit LED sign. It is available in a range of colours and can be supplied as a single-colour, single-message sign, or as a dual-colour, dual-message sign. For example it can be used to say Open in green and then it can be switched to say Closed in red. A 24VDC switched power supply is required.
Often used next to doors – or on doors – the mini LED sign is used in hospitals, universities, prestigious buildings, hotels, supermarkets, commercial and industrial enterprises worldwide.
Comment: Hydrogen requires a long-term mindset
I am not sure that a consensus is possible - unless it goes for liquid hydrogen (as an end product) - as (unless airships are revived) the parasitic...