Invisible Heating Systems is pioneering the concept of leveraging the heat absorbing capabilities of asphalt by burying a network of pipes under a road, or parking lot, which functions as a quasi solar hot water heater. In addition to generating hot water, the system also potentially reduces the use of salt in de-icing roads in the winter. The idea originated in the Netherlands, where it has been used in flyovers and airports. [via treehugger]