A solar powered fan for your attic is a good choice if switching completely to solar power is not feasible. The fan will have a temperature sensitive gauge and switch itself on when necessary. This will remove heat and lower the cost of cooling. It's also solar powered, so you don't have to pay to power it.
You have likely already made the choice to remove your reliance on fossil fuels and start a new life using solar energy as your main source of power. The technology used today is less-harmful on the environment and more efficient than what was in use years ago. Breakthroughs occur every day and every day you could be saving even more.
This is a Solar Install i did on my Mobile Home. I worked on it for several months.