I just did a quick calculation:
PV produces ~150W/m^2 for a very optimistic solar input of 1000W/m^2. PV produces this output only 50% of time (when sun is up, very very optimistic), so 75W averaged on 1 day
France Nuclear production is 61370MW [1]
To replace all the nuclear power plants, we would need 818 million square meters of PV panels, which amounts to a square grid of 30km.
Obviously you'd have to spread this along the longitude so that eastbound PVs would still be alight when the westbound have fallen out of the terminator.
It doesn't look like much actually. But I'm not counting the batteries to compensate for the night fallout, and I'm assuming 100% sun input all the time.
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