If heat pumps get inefficient at low temps could we not program them to run full blast during the warmest parts of the day and preheat the home. Thus needing to run less at night.
However for other hydronic applications such as solar water heaters there is typically a thermal storage tank which can help store heat like a battery.
Keep in mind a few things. One is some heat pumps are now operating down around -22*F. Second is geothermal is a water to water heat pump that isn't affected as much by the limitations of air temperature (but has other limitations). Third is radiant heat flooring with tubes in concrete acts as a thermal storage tank. Finally heat pumps for heating work best at low temperature hydronic water and can also be used for other applications such as DHW (domestic hot water) which needs to be at slightly higher temperatures than a buffer tank has.
I live in New England in a small house (<700 sqft), and it easily drops 5 degrees an hour when it's 65 inside and 15 outside.