U.S. patent application 20180313578 (applicant David Kreutzman, Louisville, Colo.):
"Provided herein are systems and methods directed to using renewable energy sources with hot water heating systems. The system and method provide for interconnecting a single electrical heating element of a hot water heater to first and second electrical power sources. ... To achieve additional heat storage, the inventors have recognized it would be beneficial to include a fusion pack with the water heater. The fusion pack [150[ is formed of a phase change material that is adapted to melt and solidify at a predetermined temperature. "