One website didn't give a score, per se, but it rated the payback time in years. Both houses, according to that website, would have taken about 8 years to pay off the investment, with savings after 8 years going into my pocket. That's cool and all, but I was hoping for something lower, like 4 years in Florida's sun, not the same as in the snowbelt.
The other site just came out and said that the Milwaukee house got a score of 91, while the Jacksonville house just got an 80. It recommended more panels on the FL house, resulting in more energy per year, but a higher initial investment.
The Milwaukee house had an 80/80 for something called "building solar," which is the size, orientation, and shading of the roof. The Jax house had a 66/80. Maybe it's better to have a steeper pitch on the south-facing roof, but the Milwaukee house probably loses out more on the north side than a website can predict. The biggest factor, I assume, is the sheer size of the roofs: our two story with a small garage in Florida has about 1500 square feet of roof space, while the Milwaukee ranch and larger garage comes in at just over 2000 square feet of roof with which to work.
Daylight hours and mostly sunny days are actually fairly similar, with Wisconsin getting a little more sun overall during the year. However, I'm not sure the solar scores can account for weeks in the winter when snow covers the roof. If solar shingles were installed, this might be more of an issue than angled panels, but it's a consideration in the north.
The last element that does not seem to make sense at first is the freakin heat. It doesn't help solar panels. In fact, my research (Googling it) indicates that 77 degrees is the optimum temperature, and that means Jacksonville gets several months of non-optimum operating temperatures. In fact, it makes sense why California would lead the country in solar installations. Jacksonville spends about half the year above 77 degrees as a high, and those are the months with the most daylight hours. Wisconsin, on the other hand, spends its most productive months pretty much AT the optimum operating temperature, with June, July, and August being nearly perfect solar producers, averaging a couple more hours of sunlight than Jacksonville's best months of October, November, March, and April.
It is potentially significant to note that solar panels can decrease the temperature on a roof just by being there, so that means that having them will make the air conditioner work less than not having them, but they will also stop the sun from heating a roof in Wisconsin in January, so I might spend more on heat because of the panels.
All this means that the best place for solar is Southern California, where it rarely gets above 85 or below 70 all year, and it only rains about 25 days a year. The rest of us have compromises. If you're like me and own a house up north and in Florida, then it's not as obvious as you might think which house would benefit more from solar.