Hi Canimal, yep you can buy windmills and solar panels in the buy mode. They are supposed to decrease your bills by a fraction but I usually don't bother because I always get sims no bills ever LTR.
Mostly, for my eco-friendly sims, I use the recycling bins, wastebasket for the house and big bin for next to the garbage can; no dryer but use the clothesline; use bike or Kenspa instead of a car; if you use a car, make sure there's more than one sim in it otherwise you get negative moodlet for not carpooling
, and quick showers and not baths cause sim is saving water.
Big positive moodlet for gardening and replenishing mother earth.