Quite a misleading article. They say it has the potential to be "highly efficient" in the intro. But later say it can achieve 64% of it's Carnot efficiency. If we assume their max 21C temp differential is from 20C to 41C, the Carnot efficiency is only 6.7%. Taking 64% of that, and you're looking at 4.3% efficient. That is a pretty far cry from the 300% or more that we expect from conventional refrigerant based systems.
The max temp differential may just be the initial prototype they constructed, and not an inherent limitation of the technology.
In general, capacitance isn't dependent on temperature. Capacitor temperature limitations are really just an optimization for density. There may be another choice of inexpensive materials that works over a vastly greater temperature differential.
Refrigerant-based systems are 300% Carnot efficient? Perhaps you mean Coefficient of Performance?
Refrigerant based systems aren't bounded by Carnot efficiency.
Yes, I mean Coefficient of Performance. It is directly equivalent to efficiency.
I don't understand how this thermal capacitor arrangement works, but if they're comparing it to Carnot efficiency, I assume it is bounded by Carnot efficiency. In the most common refrigeration applications, cold side is going to be -40C or above, and hot side max probably 50C. The Carnot efficiency between those temperatures are always going to be terrible to conventional heat pumps.
