Tutorial:Applied power math
In this tutorial we'll be answering the question: how much coal is needed to power a factory?
First off, we need to know: how much power does our factory use? That's easy - you can check the electricity tab by clicking on a power pole.
Here we see one radar using 300 kW of electrical power . Factorio uses real science here. The unit of power, or energy transfer, is measured in Watt (W). A kilowatt (kW) is 1000 W, a megawatt (MW) is 1000 kW, and if you're lucky enough to ever make a factory big enough, a gigawatt (GW) is 1000 MW.
So that answers the question of how much power our factory uses. To keep our factory running at full speed we need to maintain 300 kW. For ease of comparison, we'll convert that to 0.3 MW.
Next question! How much energy is released when burning one piece of coal? That's also easy, because it tells us when we hover over it: 4 MJ.
A Joule is the standard measure of energy . As with Watts a kilojoule (kJ) is 1000 J, and so on. There is a fixed relationship between Joules and Watts. 1 Joule of energy can provide 1 Watt of power for 1 second of time. So one Joule is equal to one Wattsecond. As a formula:
So to run our factory at 0.3 MW, we need to consume 0.3 MJ every second.
Quiz
How long could one piece of coal run our single radar ?
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What is the maximum size factory (in watts) a single piece of coal could run for ?
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BONUS! A metric ton of real world coal can produce about 7.2 GJ in an electrical power plant. How much does a piece of Factorio coal weigh?
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Now we have everything we need to answer our initial question: how much coal do we need to power our factory? Well, the question actually needs to be a bit more precise: how much coal do we need per second to power our factory?
Aside: why did the radar run for 20s and not 13.5s (50% of 27s)?
Quiz
How much coal per second is needed to power a 20 MW factory?
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BONUS! How many mining drills are needed to produce that much coal?
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SECOND BONUS! The average American household uses 3.2 GJ in a month (typically expressed as 888 kilowatt-hours). How much Factorio coal would be needed to power one of these homes for that period, and how many homes could a steam engine support (900 kW), assuming the power is used at a constant rate? (Assume 30 days in a month.)
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