Where did you get that map ? Those numbers seem way too high ! I couldn’t find it on the NREL site. I’d like a link so I can interpret their numbers.
Even in southern states, you won’t get more than 0.5kwh per square meter from current PV panels. Which is fine, since 60 square meters isn’t that much and would provide all the electricity the average home uses.
This graph shows over ten times the values it should. You wouldn’t get 6.5kwh even in Arizona with a 100% efficient PV. Luckily, you don’t need to. A lower solar radiation value just means you need more area, and area is rarely an issue. Only cost is an issue.