The 4% efficiency is starting from sunlight. This overstates the case, because any solar scheme wastes most of it. That doesn't mean solar energy is impractical, any more than the roughly 1% conversion (if that) of sunlight to food calories in a farmer's field would make agriculture impractical.

Also, that scheme is a thermochemical scheme for sunlight to hydrogen. Producing H2 gas by electrolysis driven by PV would be more efficient.

It's a common nuclear talking point that solar is impractical because of efficiency. This is a bogus argument, since comparing efficiency of schemes that use different inputs is comparing apples and oranges. Sunlight is cheap and abundant and can be wasted without intolerable pain.