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What is a KWh?

Wednesday, September 3, 2014

What is a KWh?

What on earth is this unit that is on our electricity bills? What does it mean and where did it come from? 1 in 5 of us doesn’t have the foggiest and the rest probably just won’t admit it!

Well by the end of this, YOU are going to KNOW what a KWh IS!

1 KWh currently costs between 7 and 14 pence and you may have already seen that one or many of these useful measures about what you can get for this money:

  • 17 hours of a normal light bulb
  • 200 hours of a super efficient equivalent bulb
  • I could do 2.5 loads of laundry at 30 degrees
  • But could only tumble-dry one load for 30mins!
  • I could oven cook 2.5 pizzas
  • And watch my 36” TV for 7 hours

If you’re happy with that, then you can stop reading now but I think you are completely unsatisfied with these run of the mill comparisons. After all, you can find these comparisons everywhere, and it’s likely that one will vary from another, so it is crucial that we all understand….ENERGY.

Here’s the fact of the day:

ENERGY CANNOT BE CREATED OR DESTROYED. It just exists and can only be converted from one form (like electricity) to another (like heat in your oven).

Pretty much all of our energy comes from the sun and it’s measured in Joules (after this English chap here called James Joule)


Everything is in Joules!

  • 1 Calorie is just over 4 Joules,
  • 1 Horsepower is 746 Joules being used every second
  • You could even measure a volcano eruption in Joules! (if you wanted to, but it would take ages!)

But how on EARTH does our sun create electricity on EARTH? I’ll give you two examples:


  1. Light from the sun makes plants grow
  2. These plants die and get buried for millions of years
  3. They become coal
  4. We burn the coal in power stations to create electricity


  1. The heat from the sun heats up the earth
  2. Different parts of the earth heat up at different rates
  3. This causes air to flow from one part to another
  4. This is wind!
  5. This wind moves the blades of a turbine
  6. This does the opposite of a motor and creates your electricity

And going back to our statement of the day, the energy stays the same, but the form of it changes. So for solar panels: light energy changes to electrical energy through some fancy stuff going on inside the panels!

Eventually this electricity comes streaming into our homes and we eat up these joules.


If we use one of these joules per second, it means we are using 1 Watt.


If we use 1000 Joules per second then we’re using 1000 Watts or 1Kilowatt (1KW).


If we use 1000 Joules per second, for 1 entire hour then we have used 1 KWh!



  • Alex Buckman
  • Posted by
    Alex Buckman
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