you say 'If you want private panels in pretty much any country outside of America, they're going to have to go on the roof as we don't exactly have the land to waste elsewhere.'

https://www.worldometers.info/geography/7-continents/ says the population density of north america is 28 people/km², and south america is 25. meanwhile, europe is 33, africa is 49, asia is 153, "australia/oceania" (???) is 5, and antarctica is 0. so basically the population density of europe is the same as america, africa is just a little bit higher, asia is much higher, and australia is much lower

possibly by 'pretty much any country outside of america' you meant either nigeria or singapore

but let's consider the worst case continent, asia. 153 people per square kilometer means 6500 square meters per person. hopefully you are aware that the average home size in asia is not 6500 square meters or even 65 square meters, and that a substantial fraction of people live in apartment buildings which share a roof. so the vast majority of land even in asia is not roofed. this is also obvious from looking at any satellite photo. but enormous numbers of people live in houses with gardens or even farms attached

if we assume a 15% average solar capacity factor and 21% efficient solar panels, 6500 square meters per person is 200 kilowatts per person. current world marketed energy consumption is something like 2, 2½ kilowatts per person. that's still too much to put on the average roof but it's not exactly a major fraction of the total land area either

even nigeria is only 250 people per square km

you're right about singapore tho