<http://schema.org/about>
"Passive solar is pretty simple. The solar part is obvious: It refers to the sun. The passive part means it works without any mechanical devices, added energy in"^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.mnn.com/your-home/remodeling-design/stories/heres-how-passive-solar-energy-works>