Looking at my electric bill, there’s a section saying “this percent came from [ex: Air conditioner, major appliances (fridge, oven), etc]”. How do they know that?
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Source – I used to work for an electrical utility company and have practical experience with smart metering.
TL;DR, they don’t, but they can make very educated guesses
In order to truly know what is going on inside your house, they would need to monitor each device in your house, which is costly. Even if they did it at the circuit level, that would be pretty expensive.
That being said, you can make some educated guesses when it comes to electricity usage. Take a fridge for example. If you need 500W to power a fridge when it is on (I don’t know the exact number, so this is just for illustrative purposes), and that fridge runs 10 hours a day, then that fridge will consume 500W * 10h = 5000Wh or 5kWh a day. Extrapolate that over a billing period and you can figure out how, roughly, how much your fridge uses. Do the same with AC, heating, etc.
When we had mechanical meters, you would need to use this estimate method because you had to measure consumption based on two readings. With the introduction of smart meters, consumption is measured as frequently as every minute. So now the utility knows how much electricity is being used on a far more granular scale. So if at 11:01am your fridge is off and at 11:02am it turns on, it will register an increase in consumption. Given the size of the increase, they can make a very educated guess at what started using electricity. They can also infer how long it was on for, which means they can make a far more accurate estimate of what was using electricity.
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