Computing stuff tied to the physical world

Electricity usage patterns

In Hardware, Software on Sep 3, 2013 at 00:01

Given that electricity usage here is monitored with a smart meter which periodically phones home to the electricity company over GPRS, this is the sort of information they get to see:

Screen Shot 2013-09-02 at 11.20.38

Consumption in blue, production in green. Since these are the final meter readings, those two data series will never overlap – ya can’t consume and produce at the same time!

I’m reading out the P1 data and transmitting it wirelessly to my HouseMon monitoring setup (be sure to check the develop branch, which is where all new code is getting added).

There’s a lot of information to be gleaned from that. The recurring 2000+ W peaks are from a 7-liter kitchen boiler (3 min every 2..3 hours). Went out for dinner on Aug 31st, so no (inductive) home cooking, and yours truly burning lots of midnight oil into Sep 1st. Also, some heavy-duty cooking on the evening of the 1st (oven dish + stove).

During the day, it’s hard to tell if anyone is at home, but evenings and nights are fairly obvious (if only by looking at the lights lit in the house!). Here’s Sep 2nd in more detail:

Screen Shot 2013-09-02 at 11.23.50

This one may look a bit odd, but that double high-power blip is the dish washer with its characteristic two heating cycles (whoops, colours reversed: consumption is green now).

Note that whenever there is more sun, there would be fewer consumption cycles, and hence less information to glean from this single graph. But by matching this up with other households nearby, you’d still get the same sort of information out, i.e. from known solar power vs. returned power from this household. Cloudy patterns will still match up across a small area (you can even determine the direction of the clouds!).

I don’t think there’s a concern for (what little) privacy (we have left), but it’s quite intriguing how much can be deduced from this.

Here’s yet more detail, now including the true house usage and solar production values, as obtained from some pulse counters, this hardware and the homePower driver:

Screen Shot 2013-09-02 at 11.52.21

There is a slight lag in smart meter reporting (a value on the P1 port every 10s). This is not an issue of the smart meter though: the DyGraphs package is only able to plot step lines with values at the start of the step, even though these values pertain to the past 10 seconds.

Speaking of which – there was a problem with the way data got stored in Redis. This is no longer an issue in this latest version of HouseMon, because I’m switching over to LevelDB, a fascinating time- and space-efficient database engine.

  1. If I read the first graphic correctly, the green integral beats the blue? Congratulations, you are a net power generator for the community. A carbon footprint heading towards a tiptoe?

    That pesky water heater illustrates how energy awareness is slow to penetrate home appliance designs. A basic control loop lets the tank temperature drift down through the thermostat’s hysteresis band and then bangs in a ~2KW load for the 2-3 minutes it takes to get the thermostat to click OFF again. That risks overwhelming the solar inverter output, requiring expensive intervention from the grid.

    A more aware design could match the heat losses with a similar trickle feed of the element at modest parts cost for a “unity” power factor ~40W supply or use a secondary heating element.

    The challenge is not in the design, but educating the purchaser that the incremental capital cost is worthwhile (the payback comes from the differential between the cost of grid units consumed and grid units injected).

  2. In the UK forums talking about this sort of stuff the terminology used is typically a little different from yours:

    Production (or generation): power from PV panels, turbines, etc. Consumption: power to appliances in the house. Import: power flowing into the house from the local network. Export: power flowing out of the house to the local network.

    Production – Consumption + Import – Export = 0 At any one time at least one of import or export is zero. If production exceeds consumption you’re exporting, if consumption exceeds production you’re importing.

    • Ah – import & export: much clearer indeed. I tend to make up terminology when I don’t know the proper English conventions, so many thanks :)

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