If you cook in bulk you will be making efficient use of your oven’s energy. Cook meals in large quantities, and set aside extra portions for another day. Professional chefs will tell you that for them cooking a meal for 6 and 60 takes almost the same prep-work.
When you’re done portion and freeze it. Reheating uses less energy than preparing a new meal and will save you time too. This will also help keep your freezer running more efficiently.