Skeptics of the transition to renewable energies in the U.S. argue that doing so will make for an unstable grid that will cost too much, but Stanford professor Mark Jacobsen and University of California-Berkeley scientist Mark Delucchi think otherwise. The two have proposed a system that combines renewable energy with underground energy storage that works on demand. The system relies on the ability to store and retrieve heat, cold and electricity in order to meet demand at all times. For example, heat captured by solar collectors on rooftops in the summer could be stored in soil or rocks, and used to heat homes in the winter. The system’s ability to retrieve heat, cold and electricity would make it able to meet demands year-round and would severely lower costs and emissions through its use of natural conductors.