Electrickery, and how to understand it.

Today I'm going to write about Electricity bills, how to understand them, and how to get the most out of them.
First of all, I'll try and explain the units. A Kilowatt is a unit of Power, and is a measure of how much energy a device uses, however, Power is Energy divided by Time (P=E/T). The energy usage of a device is often given as, say 6Kilowatts, but in order to see how much energy this will actually use, and therefore how much money it pulls out your wallet, you need to think about how long the device will run for.

It's like thinking about a car. You can't ask the question, "If a car travels at 60 miles per hour, how far does it travel?". You need more info than this, specifically, you need to know the time that the car travels for, at 60 miles per hour. If it's 2 hours, then it travels 120 miles, 3 hours it's 180 etc. This seems obvious, because it's stated in the units, miles per hour.

Watts and Kilowatts are the same, though it's not stated in the unit. A Watt is Energy (measured in Joules) divided by Time. So, when a device states that it's energy usage is 6 kilowatts, this means that it uses 6000 Joules per hour.

Multiplying the Kilowatt usage of a device by the time it's run for gives you a new unit, the Kilowatt Hour. This is a measure of how much energy a device has actually used while it's been running.

Your electricity bill is probably in Units, but these are actually the same as Kilowatts Hours. Therefore, it's easy to see how much each Kilowatt Hour is costing you, so you need to bear in mind when buying a new appliance, how long it will run for.
For instance a kettle might have a Power rating of 2kw. But you only use it 3 times a day, for 5 minutes each time. Therefore, it runs for 15 minutes per day, or quarter of an hour. So, to work out how much energy it uses, you need to multiply it's power rating by the time, so the kettle uses: 2Kw X 0.25 hours = 0.5 Kilowatt Hours each day.

A fridge, on the other hand, might have a rating of 1Kw, so you think it uses less energy than the kettle. You race out to buy an eco kettle, that saves loads of energy, and enjoy your cup of tea smug in the knowledge that you've saved the planet.
However, the fridge runs 24 hours a day, so 1Kw X 24 = 24Kilowatt Hours. The fridge uses up much more electricity each day than the kettle does. If you'd spent the money on a fridge that uses less power, then you can make a much more dramatic cut in your energy usage and your electricity bill.

More on making cuts, and saving money in the next blog.