Generator
Burns ore and coal for power. The first generator you'll build, and the only one that asks about Combustion.
Feed it something that burns. Raw ore burns for 2 to 12 seconds each, at 1 to 6 power a second, depending on its Combustion. Coal burns 2.1 times longer and harder, which is why it's worth the trip to the smelter.
Building one earns the "Power of Your Own" advancement.