Regulate the power of electrical radiator

Hi all,

I am wondering, if anybody has ever made an interface to an electrical radiator, e.g. like this one from Purmo.

I have a solution in place, where my HA steers the heaters in the rooms per Generic thermostat. This system ist convenient, since all users can individually steer their room and make individual schedules.

But, in this concept, the radiotors can have only the status ON or OFF. I cannot regulate the power of the radiator, e.g. to 10%, 50% or 100% of its maximaum power.

Has anybody some hints, about a solution to regulate the power of electrical radiator?