I don't understand what you mean about “square meter years”.
Germany is an especially difficult case, being very industrial, very densely populated, and fairly polar, though less so than, say, England.
Germany uses about 72 gigawatts of electricity and about 400 gigawatts of fossil fuels, according to https://en.m.wikipedia.org/wiki/Energy_in_Germany (but converted to SI units). It comprises some 82 million humans, so this works out to about 5 kW of fossil fuels per person. (Your "48000 kWh/year" comes out to 5.5 kW.) Generally 1 W thermal is worth about 0.4 W electric—less as transport fuel, more for industrial process heat, but generally about that. (I think this might be what you're saying about power plant inefficiencies?) We can take 0.5 W to be generous and we get 2–3 kW per person.
This would come out to 12–19 square meters of panels per person, using low-cost 160 W/square-meter panels, but those aren't average watts, but peak watts. Typical capacity factors (average÷peak) for PV installations in the US are 15–30%, so you'd normally need on the order of 60 to 120 square meters to get that much power on average, but the number Wikipedia is reporting for Germany is 10.6%. Maybe that's just a function of polar latitudes but it seems pretty extreme! Maybe something else is going on there, like production curtailment due to inadequate storage resources and demand response, or plants being offline due to equipment failure?
So I think that low capacity factor already incorporates some overprovisioning in that sense.
When I mentioned "50x", that was not because that's an overprovisioning ratio that is ever actually needed. I'm sorry that was unclear! It is far in excess of what is needed. I think 10x is pretty much the limit of what you need outside of the polar circle: instead of the 3.3 peak watts per average watt you'd need in Perú, you provision 33, and enough storage to get you through the night, and then you'll be fine even if every day has storm clouds blocking 90% of the light. In Germany that would be 400–600 square meters per person. Yes, that does mean covering 10–15% of the country in solar panels. The Germans would be well advised to put some of those panels in other, more equatorial countries, with lower population densities. Or work on demand response.
I mentioned the grossly excessive 50x number because even that ridiculous level of overprovisioning is still cheaper than a week-long battery storage system. (But not if you have to invade Egypt to install it, I suppose.) My point was that battery storage is far too expensive for anything where there is any alternative. In particular it is not a viable option to deal with seasonal variability. (Some other form of energy storage might be.)
Earth's population density is only 20% that of Germany, so getting the world's human population to be as energy-intensive as Germany without any demand response, you'd need to pave "only" 2–3% of it in solar panels. Fortunately or unfortunately, that includes the sea.