Good point - the comms satellites are not even "keeping" some of the energy, while a DC would. I _am_ now curious about the connection between bandwidth and wattage, but I'm willing to bet that less than 1% of the total energy dissipation on one of these DC satellites would be in the form of satellite-to-earth broadcast (keeping in mind that s2s broadcast would presumably be something of a wash).

I am willing to bet that more than 10% of the electrical energy consumed by the satellite is converted into transmitted microwaves.

There must be many power consumers in the satellite, e.g. radio receivers, lasers, computers and motors, where the consumed energy eventually is converted into heat, but the radio transmitter of a communication satellite must take a big fraction of the average consumed power.

The radio transmitter itself has a great efficiency, much greater than 50%, possibly greater than 90%, so only a small fraction of the electrical power consumed by the transmitter is converted into heat and most is radiated in the microwave signal that goes to Earth's surface.