The Pyrothermic Generator (PTG) is the first craftable power generator available to the player. The power per second (PPS) it generates is determined by the fuel it is burning and by the depth it is placed. Place the fuel in an adjacent hopper and the Pyrothermic Generator will supply power to any adjacent machine that consumes power. It will only start burning fuel once its internal buffer drops below half, and takes several seconds to ramp up. Each unit of fuel will burn for 30 seconds. The following table lists the power generated per second for each fuel type (on 'Plentiful' power setting).
The generator becomes less efficient the further below the surface it is placed because of a lack of air. The lowest depth it can work at is -56m at an efficiency of 10%.
08 Jan 2017: Updated to version 15.5 by Lovely Santa.