I live in a passive solar home. Mine was built in 1995. My energy costs are a quarter of my son's who lives just three streets away in a comparably sized stick built house. My walls and roof are made of SIP (structurally insulated panels) and I have a ventilation system that exchanges stale air for fresh every hour or two.
The strange thing is I didn't know it was passive solar when I bought it, it was a foreclosure, so I was pleasantly surprised when my first utility bills came in. I had an energy audit done by my utility company and they couldn't find anything to improve! :sing: