What can I do to avoid wasting energy when I’m on vacation or when I close up the house for the season?

There are several ways to save energy while you’re away:

If you are not going to be home for a while, turn your AC up to 82 degrees or higher in the summer and 65 degrees or lower in the winter. If you can program your thermostat, set it to 72 degrees for two hours every morning before the sun’s up and at 88 degrees the rest of the day to prevent mold.
For even more savings, use portable dehumidifiers (1 for every 1000 sq. ft.) instead of the AC. You can set them at 58% by sinks and showers, but make sure to have them in a place where the water can drain.
Turn off and/or unplug all of the systems and electronics you will not need like your water heater, TV, internet, toaster, microwave, etc.
Set your pool pump to run no more than six hours a day.
If your fridge/freezer is empty, turn it off (including the ice maker), clean it, and prop the doors open. If you want to leave it on, turn it to the warmest setting.