They probably run it very hot since the computer controller can prevent scalding. If the glycol elevates the boiling point, you could store energy above 100 C.

They probably run it very hot since the computer controller can prevent scalding. If the glycol elevates the boiling point, you could store energy above 100 C. The human-safe temperatures on a normal water heater must be closer to 50 or 60 C. Room temperature is about 20? I imagine if you more than double your temperature difference, you might more than quadruple your energy storage, that might offset the lower heat capacity of the glycol. Sort of like high-voltage power lines being able to use thinner wires but requiring thicker insulation (meters of air) so they don't kill anyone. User 15457345234 pointed out that you could just pressurize the water. But building a steam pressure vessel requires a weight-safety tradeoff. Maybe a mixture that boils hotter is cheaper overall than safely containing steam pressure.