The word "autarkic" means "not dependent on any support." Energy self-sufficient means that an object (e.g., a house or a device) requires no external energy. It supplies itself with energy.
The essentials Radiator Thermostat Energy Self-Sufficient BT is an example of an energy-autonomous device. Conventional smart home radiator thermostats require batteries (i.e., extra energy that must be supplied) to function. The essentials radiator thermostat operates without batteries. It draws its energy from the available heating system with the help of an integrated thermoelectric nanogenerator. This principle of energy generation is called Energy harvesting .