I live in Florida, and in my very very limited experience with outdoor tanks, tanks with no shade are going to get either green water or an algae explosion. My father had a 29 on the side of the house loaded to the gills with plants and some guppies and no matter what he could not get rid of the green water due to the ridiculous amount of sunlight. The tank would also get too hot during the middle of summer. He has a 75g under cover and needs to remove the glass tops and run a fan blowing over the top to keep it cool in the middle of the summer and even with that still struggles with temps at times.
Outside tanks could definitely be done down here, but I would use some sort of shade cloth or shading plants to get them out of the brutal sun. I would think it also helps to have a larger amount of water especially in a tub or livestock rubber maid water container on the ground as the ground will help stabilize temps.
Neighborhood Fish Farms in Miami is an outdoor fish supplier and they use large cement holding tanks for their fish. I think they use a constant trickle of water from a well to keep the tanks cool and for water changes. I've seen them use shade cloths too, but a few months ago when I went they no longer had them.
I hope my limited experience helps.