Loss of efficiency here just results in less water converted to hydrogen in the electrolysis process. The only pollution that exists in hydrogen resulting from a less than 100% efficient conversion process is water vapour.

In the case of hydrogen consumption, what is not converted to water just remains unconsumed hydrogen, we can't somehow conjure up carbon molecules in this, its either hydrogen & oxygen, or water.
It is really deceptive that hydrogen academic reference textbooks often refer to unconverted hydrogen or water escaping the energy conversion proocess as pollution. Can only guess the reason is because most hydrogen research to date was funded by fossil fuels companies.
There is no material pollution and no material losses in any of the hydrogen energy chain lifecycle, only heat, which can never be more than the heat which would have occurred had we not used the energy going to heat from the sun in the first place.
So there can never be a positive temperature impulse from solar energy use. Use of it can only ever have the effect of less temperature, never more.
This is why we should always incorporate efficiencies as part of a systemic temperature impulse, since this is what is important, if we are not so worried about where the energy at the input will come from, and the cost of it, if it even pays for its own scaling up by sales of hydrogen fuel from it, it is only the temperature impulse caused by the solar hydrogen energy chain, relative to the fossil fuel energy chain, or even nuclear fuel energy chain, none of the extracted energy chains can even come close to having a negative temperature cost, only solar hydrogen has this, only it can actually absorb and store unlimited energy which has to go to heat when nature is not storing it.
This is what I mean by energy debt to the planet, our energy debt is what we liberated to heat, which should be stored. We put it back into storage by solar hydrogen.
All makes sense to you?