I’ve been bitten by the ‘how much electricity am I using?’ bug recently – prompted by looking at my 6-monthly statement from my current electricity supplier.  $work happens to have a utilities component to it, so I asked if I could borrow one of our in-the-house whole-house electricity monitors to see if an offer for electricity service made any sense (vs my current supply).

The hookup is fairly easy – insert two batteries into the device, open the meter cabinet outside, and clamp an inductance sensor around the live tail going to the consumer unit.  Then power up the inside metering device, pair the two devices up, and get an instant reading as to how much juice the house is consuming.

So, what did I find out?

Well, my house is fairly energy efficient when it comes to electricity.  The optimal base load of the house is probably somewhere around 240 to 300 Wh (Watt-hours), assuming I turn all my electrical devices, except the fridge, off.  The maximum instant draw I could incur is in the region of 17 kW, or 408 kWh in terms of base load (which is measured across a 24-hour period).  Assuming electricity costs me 12 pence per kWh (and that’s not far off), my optimal base load costs me 2.88 pence per day.  Running a full load would cost me almost £50 a day, but I can’t think of why I’d want to run all my devices for 24 hours.

However, I said optimal base load.  My current base load is actually more like 2.88 kWh (120 Watts/hour), so the cost of the base load is 34.56 pence per day, or about 12 times what the optimal base load would cost.  Achieving the optimal base load isn’t hard – I just have to turn off the TV+Freeview+Stereo from standby (which will upset the Freeview box), and throw the mains switch for the router, Vonage device and gigabit switch.

So, what does my device consumption look like?

  • Shower – 7.8 kW on ‘hot’, 5.5 kW on ‘medium’.  Pressure on medium is a bit better than hot, but definitely not as warm.
  • Kettle – 2 kW
  • Oven – 2.2 kW when heating
  • Washing machine – 2.4 kW
  • Microwave – 1.2 kW
  • Fridge – spikes about 200 W when running the compressor
  • Computer – 200 W
  • Various halogen lights – 700 W with all of them on.

So, for summer showers, I can probably get away with the medium setting.  It’s a little cool, but I can live with that.  I already try to only turn the halogen lights on if I have to – they’re definitely not cheap to run compared to the various energy efficient 7 W sunlight bulbs that I have in other light fittings.  It looks like there are energy-efficient bulbs that can replace halogens though, so I’ll have to get some to test compatability with the sockets.  My calculations say that I should end up using 4.5 times less energy for an equivalent light output.

Time to go save a bit more money – my current daily usage is close to £1/day.  With a bit of fiddling, bulb replacement, and turning things off, I should be able to shave a good chunk of that off.

Cutting my electricity usage
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