Passive solar used to be the way everyone built... at least before way back with the Ancient Greeks and Chinese. But when we stopped relying on sun for energy, most of us stopped building this way.<p>I would guess passive solar gained popularity in the seventies due to more attention to energy conservation (oil crisis and all) and then when oil got cheap again, it wasn't so trendy. Hope that's not that case now.<p>Though cheap oil and global warming aside, I'd still prefer to live in a home heated by the sun and cooled by the earth. AC gives me a headache and I much prefer the feel of sun through a window than the blast of central heating.