Windshield melter

A water heater would be designed to survive having a frozen water tank and to melt water a little bit at a time (if the tank is frozen) and to be able to pump that little trickle out at a high temperature. The heater would be designed to take power from a vehicle's alternator. A pipe* would go from the pump to above the windshield. Within a few seconds a trickle of hot water should start traveling down the windshield on a dozen spots. Within a minute it should be enough to significantly loosen any ice build-up, allowing easy removal.

*the pipe would be designed to drain very quickly when not under pressure, so it wouldn't be blocked by frozen water