> It looks like big parts of Pennsylvania only average about 3.5 hours of sunlight per day over the year.

3.5 hours of sunlight per day != 3.5 average hours of full-sun per day.

Additionally, if you re-read your page, the number is higher than your claim of 3.5, it's 3 hours and 50+ minutes for all PA locations listed. So you misrepresented what the page describes and you misstated the numbers. What's the point of your original comment?

https://www.altestore.com/pages/solar-maps-for-the-usa

The desert southwest is only at most around 6 kWh/m^2/day, mind you.

This is horizontal irradiation; a PV module tilted properly would receive more effective hours per day. Also, half the solar intensity for twice as long would enable inverters to be downsized, even if the average kWh/m^2/day were unchanged.