This may not answer your question, but will help your curiosity.  Be carefull of thinking that solar power can run high amperage devices like a heat pump or especially an air conditioner.  Also you have to remember that all the specialists agree there is no energy shortage problem, there is an energy storage problem.  So think of your hurdle to alternative energy and payback with the storage system cost in lieu of the solar energy production cost.  I'm pretty sure you dont want to power your apartment complex at night with batteries.

I'm sure that the payoff would be beyond 10 years.  Don't be thinking that solar power will be running all those AC units during the day.  Heating is less of a problem depending on where you live.