I use these two books and lots of infographs to start this discussion. There are also a ton of authentic resources on this topic. Google in your language the term for “saving energy in the home” and voilà. This topic works really well with vocabulary for rooms in the house, household objects, and many verbs for saving, economizing, and turning off!
Here are some websites and infographs to start students looking for things they can do in the house to conserve energy. I like this one in French and this one in Spanish.
Which appliances use the most energy?
How can you make your house, school, community more energy efficient?
Have students list at least 5 ways they can save energy in the target language.