Solar panel and batteries for AC? A bit of an investment, but you can take it with you, reduce heat (blocking windows), reduce power use (for when AC is NEEDED), and make it more comfortable when it isn't. Could also be used for other stuff when you don't need AC- winter time, use it to charge notebooks, mobile phones, maybe a TV.
Lots of ways to do it efficiently, if not cheap. And solar power will always be of value
