So happens, I have a couple of windows in the basement, above ground level.
I simply attach the solar charger on the inside of the WEST window. Good voltages all day long.
PS. Then when I go on a road trip later in the Spring thru FALL, I mount the solar panel on the inside of the rear window of my "service van". THOSE DARN BRIGHT LIGHTS in the rear view mirror always keep my 12 volt system charged.