So my power company, like any other, sends regular bills reporting my usage for the month. You also get a bar graph display historical usage. If you've been a customer long enough, you'll see a full twelve months worth. I'm not totally sure of their reasoning, other than to point out that hey, summer's hot, and possibly to convince that it might be a smart idea to sign up for flat rate billing, average billing, or whatever marketing promotion they have going. You know what I see when I look at these graphs? Well, I teach Pre-Cal, so guess.
These could prove to be a lovely introduction to oscillations and be a nice "What Can You Do With This?" for a first act on graphs and/or the inevitable "why do I care about sine functions?" question.