Hydrolysis from solar is '30% efficient' of nearly limitless solar radiation. Hydrogen fuel cells emit no CO2. Its hard to underestimate what a gigantic win that is.
Unless we have enough photovoltaic energy production to close down all coal plants, the "limitless" part isn't really there. And even then it is cheaper to store the electricity directly in batteries - they are even cheaper than the devices required for hydrogen fuel cell cars. Hydrogen fuel cell cars still need a battery, though a smaller one, then the expensive fuel cell and finally the gas tank which has plenty of issues by itself.
But the relevant comparison is to batteries, which are more efficient.