But making them harder to heat in winter.

Is that a problem if a majority of the energy for heating is renewable?

How so?

I have solar PV on my roof and it makes no direct difference to the heating required. Except that I have a little generated energy that provides some warming inside from the appliances that it powers.

If solar panels block the sun from heating the roof in Summer (making it easier to cool) then the reverse is true in Winter. Some amount of free energy is no longer hitting the roof and potentially changing the energy equation.

Is it a meaningful difference, I am not sure. However, it is only fair to count the impact on both seasons. Heating costs are significantly higher than cooling (larger absolute temperate delta required to go from 30f to 70f than 90f to 70f)

There is no meaningful solar heat transmitted in through the roof in winter, at least in a climate and building like mine, which is fairly typical.