From Unofficial Stationeers Wiki

The RTG - Radioisotope Thermoelectric Generator is a power source currently only available in creative mode. It provides a limitless supply of power, with a potential for 4.0kW. The RTG is placed on the same grid as wires, allowing to fit 3 on top of a single frame.
They do require they are placed on Frame structures, either iron frames or steel frames.