kW and kWh

ComplexP

I just heard a factoid on Radio 2 (which I love by the way) saying that Google uses more power per year than some countries to power its search engine which is quite interesting.

But predictably they quoted the figures in kW, ie. 'Google uses x amount of billions of kW per year'.

I keep hearing this mistake in the media and it's starting to annoy me.

kW is an instantaneous measure. kWh is accumulated total.

So for example, if your electric heater uses 2kW of power that means it is using 2kW of power if it is on, full stop. If you leave it on for 8 hours, it's used 2x8 = 16kWh (kW Hours) of energy during that time.

It's a small thing but I wish they'd get it right.

busenbust

Agree, semantics for pedants

ComplexP

I'll take that as a compliment

I'm not pedantic about everything though, that would make me strange.

But understanding what your quarterly energy bill is saying is quite a handy skill to have, right?

busenbust

^Lol, I agree with you, and points well illustrated

ComplexP

Perhaps we should start some sort of 'Definitions' thread where all of the everyday technical terms people get confused about can be laid out in simple terms with examples?

Like quoting your broadband speed in MBits, which is fine. But quite a few people don't know what a MBit is. It's not MByte per second, rather 1/10th of a MByte per second (I think, I'd need to look it up).

So if you have a 10Meg file to download and you are on a 1MBit connection it should take about 100 seconds or 1m40s to complete.

timbim_2

ComplexP wrote: »

kW is an instantaneous measure. kWh is accumulated total.

Right idea, slightly awkwardly phrased. The Watt is the SI unit of power, which is the rate of energy use; thus one Watt is one Joule of energy used per Second. The kiloWatt hour is a measurement of energy, as when talking about domestic power consumption, the Joule is just a little on the small side. It should be fairly obvious that one kWh is 1,000 * 60 * 60 J, which is a big number.

ComplexP

Thank timbim

I did deliberate over that wording so your point is well taken; it was a little awkward.

I didn't want to get too technical with the definition. I guess what I mean is that kW is something that must be measured instantaneously and cannot apply to annual consumption. For example, right now my computer is using 0.13kW but in a minute's time it may be using 0.22kW.

The whole 1 Watt = 1 Joule per Second thing I considered to be getting a bit much...

busenbust

Perhaps we should start some sort of 'Definitions' thread where all of the everyday technical terms people get confused about can be laid out in simple terms with examples?

Nice idea :cool: We do have this...

ComplexP

That's pretty good, but only about ADSL terms, right?

busenbust

ComplexP wrote: »

That's pretty good, but only about ADSL terms, right?

I'm not certain if there's a hard and fast rule; perhaps refer to a Moderator?

bazster

ComplexP wrote: »

Perhaps we should start some sort of 'Definitions' thread where all of the everyday technical terms people get confused about can be laid out in simple terms with examples?

Like quoting your broadband speed in MBits, which is fine. But quite a few people don't know what a MBit is. It's not MByte per second, rather 1/10th of a MByte per second (I think, I'd need to look it up).

So if you have a 10Meg file to download and you are on a 1MBit connection it should take about 100 seconds or 1m40s to complete.

<pedantry>
In referring to broadband bandwidths lots of people say "megabytes" when they mean "megabits", which drives this pedant crazy.

A megabit (Mbit) is 1,000,000 signal pulses per second, and is a measure of communications bandwidth. A megabyte (Mb) is 1,024 kilobytes (Kb) (which in turn is 1,048,576 bytes, or 8,388,688 bits) and is a measure of data size.

If you want to know how many Mb of data you can pump though a line of given bandwidth in a given time, the maths is simple using the above numbers, but to express bandwidth in terms of megabytes is just plain wrong.
</pedantry>