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[Dray]

Would a kWh be 1000 "Watts per hour"?

[Chrysalis]

I meant units so killowatts, sorry.

Again this must sound pedantic, 'Watts' are a measure of power, whereas but 'units charged' will refer to energy, not power.  Most suppliers state their units in kWh for billing purposes.

However... a 5W device, over 24 hours, will consume 120 Watt-hours, or 0.12kWh.  With shifting of a decimal point, than can obviously appear as  '12 somethings' on a meter's display.  Could that be the '12' in the question, and explain what you are seeing?

no you dont need to explain anything, I know how it works.

SO lets make the question even more simple, what would you do if there was a huge discrepancy between own measured usage and the meter?

220 watts on 24/7 measured at approx 5kwH but meter shows 12 units per day.

[roseway]

Would a kWh be 1000 "Watts per hour"?

No, watts are effectively a speed, so watts per hour would be an acceleration, not a quantity.

[Chrysalis]

Would a kWh be 1000 "Watts per hour"?

No, watts are effectively a speed, so watts per hour would be an acceleration, not a quantity.

ok so if they different what kwh is someone using if they have a 1000watt device on all the time and nothing else and we assume the power efficiency is 100%. isnt a kilowatt 1000 watts? so 1 kwh logically is 1000watts.
But it seems the electric companies complicate it by multiplying it for each hour in the day so with 24 hours in a day the kwh number is not a true per hour consumption.
so if I was using 1000 watts every hour, it wouldnt be 1kwh it would be 24kwh?  really it should kwd killowatts per day

[sevenlayermuddle]

I was about to draw comparison with a car's speedometer, in miles per hour.  You cannot simply invert the last dimension, to express 'mile-hours', which is a useless quantity.  Or so I thought...

But... a quick search reveals that mile-hours are sometimes used by highways agencies to assess the badness of roadworks... roadworks that cover a long distance are obviously bad, as are those that last a long time, so mile-hours are a useful term after all.   

And I'm becoming convinced that watts-per-hour must have a use too, perhaps in assessing how effectively a power station can adapt to a surge in usage?

[HPsauce]

If any of you REALLY don't understand this sit down with someone who is proficient in Physics and get them to ensure you understand.

No, watts are effectively a speed

[HPsauce]

And I'm becoming convinced that watts-per-hour must have a use too, perhaps in assessing how effectively a power station can adapt to a surge in usage?

Probably measured in Megawatts per minute or similar.

I recently went on a tour round Cruachan http://www.visitcruachan.co.uk/ and that can respond in a spectacular fashion to increased electricity demand.

It can, if "ready to go" switch from zero to 440 Megawatts in 30 seconds! 

[Dray]

Would a kWh be 1000 "Watts per hour"?

No, watts are effectively a speed, so watts per hour would be an acceleration, not a quantity.

But it was just said Watts are a measurement of power 

[roseway]

Would a kWh be 1000 "Watts per hour"?

No, watts are effectively a speed, so watts per hour would be an acceleration, not a quantity.

But it was just said Watts are a measurement of power 

Power is the rate of flow of energy (electricity in this case), and is analagous to speed.

[Dray]

But when someone says "one Watt per hour" they surely mean "a Watt-hour"? That's what I mean.

[c6em]

We power engineers measure really big usage in MVA's not MW.
This is because the power factor becomes a significant issue so the MW figure is not used much
Indeed if you are operating a zero power factor the MW are zero - but the MVA and hence the current and therefore the excess heat generated is certainly not.

[sevenlayermuddle]

We power engineers measure really big usage in MVA's not MW.
This is because the power factor becomes a significant issue so the MW figure is not used much
Indeed if you are operating a zero power factor the MW are zero - but the MVA and hence the current and therefore the excess heat generated is certainly not.

Welcome to this curious debate.

Consideration of Power Factor is the reason I have sometimes tried to use the phrase 'energy for which you are billed' in this thread, rather than just 'energy'.

And of course, old fashioned incandescent bulbs generally used to have unity power factor, whereas CFLs and LEDs are often much worse.   Which further emphasises the whole point I keep trying to make, that it is dangerous to assume you are saving the planet (or your wallet) just because you use more 'efficient' electrical devices.  You probably are saving both to some small extent, but probably not to the extent that you may think.

[Chrysalis]

power saving in the long run never saves the wallet, because the power companies always counter with higher prices to maintain profit.

if someone invented a device tomorrow that halved electric consumption and everyone was given it, then the next day prices would double.

[Dray]

So if I have a 20W CFL and a 100W bulb, does the CFL use less units of my electricity than the 100W bulb?

[Ronski]

Yes,  it's only using 20w,  compared to a 100w, so it only costs a fifth to run.

Basically 1 unit of electric is a 1000 watts used for an hour, so our 20w bulb will take 50 hours to use 1000 watts, whereas the 100w bulb will only take 10 hours.

The new LED bulb (8.5w) I've just purchased for £13 would take 95 hours to use 1000w, this replaced a 25w CFL, which replaced a 100w incandescent bulb. I'm very pleased with the LED, it is instant on and is nice and bright.

Now a 100w normal bulb probably costs about 85p, now my LED bulb costs £12.15 more, to use £12.15 worth of electric I'd need to have my 100w bulb on for 1050 hours or 43 days, or 2 hours per day for around 1.43 years.

So over the lifetime (it has a 5 year guarantee) of the bulb I will eventually start saving money, and save the price of the bulb many times over.