Monday, 22 April 2013

How much for an itemised electricity bill?

Can you imagine going to the supermarket and filling your trolley with stuff without prices on and then getting a bill for the total and never knowing how much you could save by making different choices? Of course not, but that is what we do when we pay our electricity bill. We have little idea how much of that bill is due to the TV, or the fridge-freezer, or the washing machine, or the lights, the wifi router,... There are lots of websites which will try to give you some clues (some listed below) but in practice it is impossible to know without measuring, which means a lot of expensive special plugs and/or wiring. An average fridge uses 162 kWh/year but yours could use half this or double or more[1]. In fact there is a much easier way to get a partial answer by monitoring the whole house electricity use at least every second. Looking at the total power draw you can pick out 'events' when items are switched on and off and it is possible to recognise at least the most important appliances like TVs, washing machines, fridges and freezers and how much energy they are using. Would you like to know this? How much would you like it?

It is hard to sell this service because there are no direct savings from it - you won't know how much you can save until you try it, and even then the value comes with continuing use. Companies such as AlertMe and Onzo have at least some of the capability but they aren't selling to domestic customers. Starting in 2014 we will all be getting smart meters. Wouldn't it be great if they could do this? They won't. It would be possible to have them do it - but unless there is a demand for the service it won't happen.

Analysing your electricity use in this way is called disaggregation and it is difficult. You need to know the signatures of different appliances and they vary. For example, the characteristics from a fridge will vary between makes and models and also depending on the temperature, how often the door is opened, what has been put in it, whether it is functioning correctly. There is an excellent description of the problems on Jack Kelly's blog here.

Through my consulting work I have seen electricity profile data that shows a fridge going wrong. It starts out looking like a normal fridge turning on and off with the thermostat every hour or so but a few months later it is on permanently. The extra electricity use is about 1.0 kWh/day, adding nearly 10% to an average bill. I can't say from the profile what has gone wrong: it could be a dodgy thermostat or it could be failed door seals, lost refrigerant or something else. I can say that fixing this would save £50/year. However, even if you noticed an increase in your bill, how would you know what was causing the problem without a disaggregation service?

If your teenage son, home for the summer, left his computer and monitor on day and night in his bedroom would you know? And even if you did would you have a clue how much this was costing you each day? It could easily be five times as much as the dodgy fridge. This happened to an acquaintance of mine and was not discovered until after the bill arrived, by which time the son was back at university. It took a deal of detective work to identify the cause.

These are unusual cases (though from the electricity profiles I have seen about one in thirty fridges are faulty) but even with a basic real time energy monitor without disaggregation you can usually save 5-15%. (Turning energy monitoring into energy savings). How much more could we save if we knew better where it was all going?

There is a great deal of cynicism about smart meters since the only definite savings will benefit the supply companies by not having to employ meter readers. Whether or not that translates to reduced bills for us only time will tell. There are potential savings for us from time-of use pricing (see Smart Meters will save us money if we take advantage). However smart meters could deliver a great deal more services, if we want them and are prepared to pay a bit extra for them.

Household energy consumption tips and tools:
Home Electricity Usage Calculator ( - my website)
Household Energy Consumption (Carbon Footprint)
How much do households appliances cost to run (

Some companies already have disaggregation capability:
Onzo Sells Hardware to SSE, Focuses on Analytics (GreentechGrid)
Smart Data (AlertMe)

[1] Household Electricity Survey A study of domestic electrical product usage


  1. Interesting, if our fridge ended up using that much it would be 20% of our bill or more.

  2. Nice one! I like the outfit of the characters. Wish i could do the same thing too but im not that techie.i like the outfit of “from farmer to warden”.. really interesting solar installer