I need to have my foundation repaired before I even consider new windows or putting solar panels on the house. I have two heat pumps and they are pretty efficient (heating and cooling) and insulation in the attic. Those things I did when I first moved in. The foundation is the stumbling block - way expensive to think about right now, so the rest waits. I don't know if all of those changes would add even the amount spent to the value of the house.