Another great idea hiding in plain sight: Redirect heat from asphalt road and parking surfaces for productive uses. Several years ago I visited a house that had rooftop solar thermal panels plumbed to tubes embedded in the driveway. During the summer, the asphalt surface acts as an additional solar collector for domestic hot water. During the winter, the driveway loop can be used to melt snow. Imagine how many BTUs could be pulled from a Walmart parking lot in midsummer. --b.d.s.