12 hours/day is the average solar duration. You'll get more than 12 hours of sunlight in the summer and less in the winter, but it'll average out.
And sure, if you park under a tree or let your panels get dirty, you'll reduce the amount of charge you can get. Same thing if you park in a garage or paint the roof. We can sit around all day and come up with ways to kill the performance. But you can just choose not to do these things.
Even IC engines have ideal conditions like don’t use a lead foot and light on the brakes, but the average driver isn’t getting the ideal MPG. Similar issue with solar.
Kinda think govs should mandate one per suburb street to give people a mobility option, especially when they don’t require full licence.
700W is perfectly reasonable. I have a 200W panel acting as shade over a tricycle which is much smaller and can easily charge a 1kWh battery in a day..
12 hours/day is the maximum possible solar duration so you really need to cut that in half to account for a full year on Earth. So we're down to 1 kWh/day and realistically much less if you happen to park under a tree or a bird poops on your roof. That will hopefully get you to a charging station but not much further.