Look after the pennies...

I'm going to assume that you know the other half of this little proverb.

I don't want to quote it in full because this is one proverb that I truly can't stand.  It makes no sense! It's just not true! If anything, it's the other way round: If you make big investments in things that work well and last a long time, you'll never have to worry about the minute details ever again!

And so it is with energy.  When people talk about home energy-efficiency, the first thing that pops into your head is... let me guess... low-energy light-bulbs. Great! But as far as I'm concerned, low-energy light-bulbs are the "pennies" of energy-efficiency. Yes, by all means install them in your homes, but don't expect them to take care of the bulk of your home energy-efficiency.

To demonstrate this point, let's compare boiling a kettle unnecessarily to leaving a light on unnecessarily. Have a look at these calculations:

Boiling a kettle: 3kW for 3 minutes (1/20th of an hour)

3 kW x 1/20 h = 0.15 kWh 

Time for a 60W lightbulb to use the same energy:

0.15 kWh / 0.06 kW = 2.5 hrs

Time for a 11W lightbulb to use the same energy:

0.15 kWh / 0.011 kW = 13.6 hrs

What that's basically saying is that to waste the same amount of energy as boiling a kettle, you would have to leave a 60W incandescent light-bulb on for 2.5 hours.  Or if it was an energy-efficient light-bulb (11W), a whopping 13.6 hours!

The other thing about kettle-boiling is that it is a huge demand for a short period of time, which, if large numbers of people turn them on at once, as Chris mentioned on monday, causes a peak in electricity demand that can be in excess of the entire electricity production capacity of the country.  Electric lights, however, are a more constant demand and can be allowed for much more easily - 273 low-energy bulbs would have to be turned on at exactly the same time to create the same effect as a single kettle switch being flipped!

So which should we pay more attention to? The "penny" light-bulbs or "pound" unnecessary kettle-boiling?

It's still very hard to keep you eye on where you're using your electricity though, because it's so invisible and so available! You can just flick a switch and it's there, but this hides the amount of energy you're really using.  Say you've got an electric heater in your living room (as indeed I have, although I rarely use it), it would be quite easy to turn it on and leave it on without a care in the world, and to be barely aware of the energy that is going into it.  With a woodburner, however, if you were spending 10 minutes every couple of hours going out to the shed to bring in some more wood and stack it up in the burner to get the same effect as a 2kW electric heater, you'd start to think to yourself "What the hell am I doing? Look at all this wood I'm wasting!"

Perhaps you'd see your electricity bill differently if it was itemised, like a telephone bill:

This week's electricity usage:      Cost per Use      Total
Dishwasher Use x 8 .................................. £0.15 ......... £1.20
Washing Machine Use x 2 ........................ £0.20 ......... £0.40
Lights in living room x 28 hrs .................. £0.003 ........ £0.10
Cooking x 10 ............................................ £0.15 .......... £1.50
Microwave x 6 ......................................... £0.15 .......... £0.90
Washing hands with hot water x 20 .......... £0.02 ......... £0.44
Power shower using electric immersion heater x 7
................................................................. £1.01 .......... £7.07

Which would you look at first?  The lights? Or the power showers?

Whether the shower or the tumble-dryer takes the most amount of energy in your house will depend very much on your set-up, appliance energy-efficiency and heating energy-source, but you can depend on one thing: you're not going to have a big impact on your bill without looking at the pounds, not just the pennies!

Images: Three pounds and one pence by Simeon Jackson (who noticed that there are three pound coins in the bin in the corner of the picture?  Who's looking after them now, huh?), Kettle switch found on the internet, annotated by me.