Learn About: Measuring Energy

Ok, hands up who knows what a kiloWatt hour is?

What about a Watt?

Yes this is a bit of a reminder of some school science of how we measure electricity and other energy.

Why learn about this?

The reason for knowing about this is that it helps use see better where the energy is being used.

It’s well worth understanding the language of energy as it really helps in our quest of reducing its use.

So if you’re unsure what a kiloWatt-hour is, all will be revealed in the next few lines !


Power:

Well firstly, Power is the rate at which something will draw energy. Power is measured in Watts. For instance, a kettle might draw 2000 Watts, a laptop 100 Watts or a low energy bulb 8 Watts.

These are sometimes expressed in kiloWatts (kW). So the kettle would be 2 kW, the laptop 0.1 kW and the bulb 0.008 kW.


Energy:

Energy on the other hand is the amount of Power drawn over a given Time. Put simply, the longer you leave something on, the more Energy it will use. So running a kettle for 2minutes will use twice the energy as leaving it on for 1min.

Energy is simply Power x Time. And if the Power is in kW and the time is in hours you get the standard unit of Energy, namely the kiloWatt-hour (kWh). Exactly the same units as your electricity meter.

So if your kettle was 2kW and you ran it for an hour it would consume 2 x 1 = 2.0 kWh

Equally, running your 100W laptop for 8 hours would consume 0.1 x 8 = 0.80 kWh

Or that 8 Watt bulb on for 24 hours would use 0.008 x 24 = 0.192 kWh

You get the idea. Just make sure that the power is in kW and the time in hours and everything should be fine.

So what's going on in my home?

In terms of energy use you’ve generally got two different things going on at home – Big Stuff and Small Stuff (to use the technical term).

 

1. Big Stuff

 

Firstly there are the Big Power items (like kettle, oven, tumble dryer). These are things that shamelessly gobble up lots of Watts – or kilowatts more like. You may use them a lot or maybe just a little, and the Energy they consume will depend on how many hours they get used.

If you want to cut your consumption and associated Carbon emissions here, either find lower energy alternatives or simply use them for less time. Hence the mantra of “only fill the kettle with what you want” or “use a drying line instead”. It’s all about getting those kWh’s down by cutting down on the time that these Big Power items are on.

 

So an example would be the kettle – say it’s 2kW and it’s actually making tea for about a quarter of an hour a day. That means energy consumption is 2 x 0.25 = 0.50 kWh.

 

2. Small Stuff

 

At the other end of the spectrum are the smaller power items that normally slip beneath the radar, but are frequently powered up 24hours a day. Things like power-packs for computers, stereos on standby, fridges, actually anything on standby.

On their own their power consumption is small, but their total energy consumption can be high. This because a) they are on 24 hours a day, and b) there are just so many of them everywhere!

 

So just taking three things on standby, ie: plugged in, but not actually on (a stereo using 6W, a computer power-pack 8W, and washing machine 8W) gives a total of 22 Watts on standby. If these are on 24hours / day, they’re using 0.022 x 24 = 0.528 kWh.

 

But just a minute - checking back to the kettle above, shows that these three on standby are using about the same as all your daily tea-making activity.

 

That’s nearly 200 kWh / year for no apparent benefit, which while costing you £25 annually is costing the Earth a whopping 100 kg of CO2 each year just for three items on standby.

Just by pulling the plug on the things in this example you will be saving the world 100 kg CO2 each and every year (definitely calls for a cup of tea!)

 

Anyway, armed with the knowledge of what’s a kWh we can make informed decisions about where to save.