I lost power for three days two summers ago - thank goodness it wasn't incredibly warm, but it was warm enough. Try to do as suggested above, especially in providing lots of water - I put bowls in every room in the condo.
Did you have an electrical inspection when you made your offer? Sometimes a older place needs to have a fair amount of electrical upgrading before adding newer lines in. My place is about 30 years old and were I to add any more major appliances, I'd have to have a major electrical overhaul. I do suggest making sure your guy is a licensed electrician, not just a handyman. Good luck!