There are many solar plants not mapped due to lack of high quality, up-to-date aerial/satellite imagery, or volunteers.
Germany is country mapped best, not necessarily having significant share of solar.
Might also be how it’s displayed. Germany has quite a bit of solar but its less concentrated in giant solar parks and the country is smaller than US, China, or India.
So for example US has multiple solar farms over 500MW and several over 200MW but none of Germany’s solar farms are over 200MW and only 4 are over 100MW.
A quick google tells me that as of 2021, the US had ~23GW of installed solar generating capacity, and Germany had ~59GW. As the US has roughly 4x the population of Germany, that means that Germany has roughly 12x the amount of installed solar capacity per capita.
In addition, the US govt says [0] this year should have added 46,100 MW to the total. Electrek, if they are accurate, predicted an additional 5,600 MW on residential rooftops in 2022 [1].
So for example US has multiple solar farms over 500MW and several over 200MW but none of Germany’s solar farms are over 200MW and only 4 are over 100MW.