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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Some of these answers are close, but not completely accurate. I create and implement energy policy, and have a lot of background with this exact question. Generally, the types of reports you’re receiving are called Home Energy Reports (HERs). 99.9% of utilities, probably 100%, contract with third-party vendors who actually run the algorithms and help construct these reports.
In many areas, smart meters are ubiquitous. You may also see these referred to as “AMI” – Advanced Metering Infrastructure. The vast, vast majority of the appliances/electric (or gas) usage in your home cannot be disaggregated. Run-time data from smart devices (like smart thermostats) can be gathered, but this is not utilized in these reports – it’s way, way too granular and getting the data feed from Google (Nest) to the HER vendor would take way too long, is often anonymized, and has limited additional value.
Instead, much simpler algorithms are used but still have a pretty solid degree of accuracy. For example, if your usage in the cooling months spikes compared to the baseline, it means that is from your cooling load. Conversely, if your electric usage spikes in the winter, it means that is from electric heating. If it spikes in both directions, it could mean you have a cold-climate heat pump.
From there, you can make some other inferences with a good degree of certainty, i.e. lighting makes up X load of baseline usage on average, your baseline is Y, therefore it’ll show lighting will result in Z kWh on your report, and the same can be said for other usage. These reports are NOT disaggregating individual appliance usage, including bi-directional smart-home devices, even if they’re included in load shedding programs, unless you’re getting very specific load shed (demand response) emails based upon specific device enrollment (normally smart thermostats, could also be EV chargers, heat pump water heaters etc.) but even so they won’t know the exact usage from lighting, your dishawasher, your TVs etc.
I was looking at my “home energy report” tonight as I was tossing mail in the shredder. What’s with the assertion that my home uses 5x KWH compared to average homes in my area? and about 7x as much as an “energy efficient home”? I remember reading something, I think it was in a Malcolm Gladwell book, about the effect of hanging flyers on doorknobs informing residents they were either below, at, or above their neighbors in terms of electric consumption, and they reviewed the results of the household’s subsequent energy use based upon the comparison they fed the household. Is this just a psychological trick, or actually correct? I work for the State in welfare, so I see a lot of electric bills, and mine isn’t that much crazier than most, but I will admit the bills I usually see are from the bottom of the socio-economic rungs, so my samples may be skewed.
I had a new panel installed and the city tried to tell me they need to have CTs installed at each breaker so they can monitor usage of each circuit. They said it was part of a new effort to reduce wasteful power usage. They also required a smart breaker after the meter so they could turn off power in the event of fire. So I went from the meter into my main breaker, to my ATS, and then to the main panel, to my whole house UPS, then to the house panel. I used regular breakers and will not be allowing anyone to connect to or monitor anything. None of their business. They are upset that there are capacitors in my design that buffer any motor signatures. My usage is steady to charge the UPS. I also augment with solar and a genset. They had a fit when I wanted 3 phase power in my home at 480v. I did install CTs on everything so I can monitor, but they will not get access to it. And I will never use wireless devices to monitor anything. Too easy to hack in and take over. Hard wired with shielded twisted pair.
Explain like I’m five is the sub, what a strange question for this sub but holy hell are there some amazingly in-depth responses!
Let me try.
Some things we use like our lights don’t use much electricity, the TV and hair dryer use more, and things like the air conditioner use a lot. The people that make and send us the electricity can see how much we use because they are the ones giving it to us! Ok bud good question hope that made sense, here’s some apple sauce then you can go play outside!
They’re guessing based on the change in current draw when things turn on and off. It’s a fairly educated guess. They can’t tell the difference between an air conditioner or large air compressor, for instance. They just know something was sucking some major juice.
They do some educated guesses. My server is considered “heating” on my electrical bill. Which is harsh, but probably more correct than I’d like to admit.
What they are doing is called “load disaggregation” and it is a very broad and hot research topic in energy policy academia. In nearly all cases, appliances are not monitored directly, and usage is estimated using algorithms. The methods they use for this estimation are non-trivial and there are many competing methods. These look at appliance signatures (unique characteristics of each appliance), the times at which your loads are used, the temperature on that day, etc. Such data is very useful for “demand response” markets and it will likely play a big role in renewable energy adoption.
Smart meters will monitor how much power is being consumed at a specific time and then use that number to make an educated guess, for example most microwaves are around 1000 watts, AC around 2500 watts, water heater 3500, etc.
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.
Machines don’t all use electricity the same way. Example a AC motor has very unique finger print that it gives out as it runs – as in example your AC’s fan. Digital devices like computer’s power supply also draws electricity in a specific way – it does take a constant pull but rather more like pulses that it averages out in the powersupply to steady DC with the help of capacitors and diodes. You can imagine this like a barrel getting filled with water and as it empties from a hole at steady rate you only need add water every now and then to keep the flow steady. A heating element pulls a steady flow in both directions with steady changes in the properties because heat chancing the properties of the material element is made of, and that suddenly stops now and then as the thermostat shuts it off.
The electric companies have studied and sampled all appliances; then they can see from your electric meter the way you are pulling energy. They can break down the wave forms from the different phases (and ground if you live in places where the phases are in star formation (120V) and not in delta (240)). Since they know you are a residential power user it is with high likelyhood that you poweruse are from certain kinds of devices and looking at the energy use and waves in the phases they can pinpoint with fairly high accuaracy what devices you use.
When you use AC power, the load added to the system basically just only chances the relationship of voltage and current. These are very easy to measure and statistically break down.
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