Question: I recently purchased an 18 kW whole-house propane-fueled generator. Wasn’t cheap — just trying to keep my family safe with all the weird weather lately. My question is pretty basic. How does the propane actually get transformed into electricity? — JMS, Neshkoro, WI
Answer: I empathize with your weird weather worries. Did the same thing here, but with solar panels and a backup battery. To answer your question … propane doesn’t “actually get transformed into electricity.” The heat energy released by burning propane in an internal combustion engine allows it to push the pistons and spin the crankshaft. The crankshaft is mechanically linked to the generator, which is the device that actually makes your electricity as it spins.
The video shows an electrical generator stripped down to its basics. All you need to generate electricity is a moving magnet and a conducting wire with free electrons. The magnetic field (B) will exert a force (F) on the electrons (Q) that depends on the speed of the magnet (V). That force follows the Right Hand Rule, which is a vector cross product involving three dimensions. The equation is: F=QV×B:
As the magnet rotates between north and south poles the electrons first move one way, then reverse themselves, producing what is called alternating current (AC) — the type of electricity that powers almost everything in your home. So electricity doesn’t actually “flow into your home.” The electrons in your wiring simply oscillate back and forth from their original positions. But they still deliver energy.
Here’s a video that shows the effect in action. We have a magnet suspended like a pendulum, and as it swings back and forth it passes a coil of wire connected to a microammeter. You can see how every pass of the magnet cause a small electrical current to flow in the circuit:
Just like in a commercial electric generator, this one produces AC but with a frequency of ≈1 Hz. What’s delivered to your home is 60 Hz which all appliances are designed for. A few microamps isn’t much electricity but this simple generator shows the basic principle.
Real commercial electric generators, like the one below, output hundreds of megawatts of electricity with a current on the order of thousands of amps (depending on the output voltage). They are finely balanced machines that run nearly constantly at thousands of RPM, and with negligible vibration:
These large generators are connected to a turbine that’s spun by high-pressure steam. The fuels used to create the steam are coal, natural gas, various grades of petroleum, and uranium (which isn’t really “burned” in the conventional sense), as well as geothermal heat provided by the deep Earth. In the case of hydropower or tidal power, the turbine is spun by falling water.
Smaller versions of these generators are used for everything from cars to wind power to your whole house generator. 18 kW is a robust output. 5kW will handle a basic load, like your essential appliances (refrigerator, lights, TV, laptop, sump pump), whereas 25 kW will run pretty much everything, including your HVAC. The energy efficiency of your appliances and the thermal insulation of your home are huge factors.
As a historical note: The first electric generator was invented Michael Faraday in 1831–32, but it was more a “proof of concept” than a practical machine. The first commercial generators arrived in the 1880s thanks to giants like Westinghouse, Edison, and Tesla. These days, generators produce 94.5% of the electricity used globally. The remaining 5.5% is produced by solar panels, which don’t need a generator or turbine.
If you’re interested in learning more about utility-scale generators, and the impressive engineering that goes into building and maintaining them, I highly recommend this article written by electrical engineer Ben Adams: The Power Generation Game.
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