Smart meters: what to know before you get one

In the last few days I’ve got two unsolicited emails, apparently from the utility company that serves my flat, with the following wording:

We’d like to offer you a free, brand new smart meter, giving you control of your gas and electricity usage.

Right, before you’re tempted to have one installed “for free”, you might want to know what the potential is and why it isn’t good for you…

Utility companies can remotely switch smart meters to stop measuring real power and they can start charging for apparent power. If they do that, and some countries do that already, it will pay for the smart meters in the long run and enrich them further too: it’s a money-making thing for the utility companies. It’s just because they want to make more money.

Let’s focus on an example here. In my case, a cheap LED light that puts a fair amount of light is drawing 92 milliamps. The power factor is about 0.113, which is awful, and it’s putting out 2.5 watts of real power. However, what I’m going to get charged for, if they switch to apparent power readings, is 0.092 times the mains voltage. I’m going to get charged the equivalent of about 22 watts for a lamp that isn’t actually putting out as much light as what a natural 22 watt tungsten lamp would have done.

If you were monitoring purely current, 92 milliamps would look quite high. However, if you monitor current-voltage, as meters are supposed to do, and measure real power, then it would actually show you what a load was really drawing.

Power companies will justify charging more because the cables that come from the substation (to your house) have to be rated to take the current of the load. So they will be seeing the 92 milliamps in my case, even though it’s not actually representative of the real power. That’s going to be their justification.

Most domestic LED lights use a driver circuit with a very low power factor (often based on a capacitive dropper circuit), usually in the 0.1 – 0.2 region, meaning the apparent power usage is 5 – 10 times the real power usage, and so will be your “smart” bill compared to your current one once smart meters will start measuring apparent power, if your loads have similar awful power factors 🙂

You’ve been warned.

About Luigi Di Fraia

I am a Senior DevOps Engineer so I get to work with the latest technologies and open-source software. However, in my private time I enjoy retro-computing.
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