Talk:Kilowatt hour

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Contents 1 Identities 2 B.O.T.U. 3 The attempted demise of the KWh 4 Reasons for the request for help? 5 approximate price in United States 6 Convenience of kWh vs Joule 7 kWh/yr - seconds, hours and years 8 Milli? 9 cal/kcal 10 seconds and hours 11 Citiations Needed 12 Watt-hour?? 13 kWh 14 Question on kWh from top 15 Requested move 15.1 Discussion 16 Post-move discussion 17 Revision by Unfree

[edit] Identities

A 60 W light bulb consumes 60 W of power. This is the same as 60 J/s or 216,000 J/h or 60 W·s per second or 60 W·h per hour.

This makes no sense. 24.94.17.47 04:55, 22 Mar 2005 (UTC)

What is the problem?--Patrick 09:24, 22 Mar 2005 (UTC)

I think it can confound certain readers and could be stated in simpler ways. AppleJuggler 05:10, 5 June 2007 (UTC)

[edit] B.O.T.U.

The B.O.T.U. is an alias ... for the kWh or the Wh?

kWh --Ali@gwc.org.uk 20:18, 4 October 2005 (UTC)

[edit] The attempted demise of the KWh

In Australia, all our energy bills are now in joules (and their SI multiples).

While this does allow comparison between gas and electricity prices (for example), it also makes the electricity bill less intelligible to many. Many people would know the cost in KWh of having an electric radiator running overnight, or even of leaving a 60W light globe running 24/7, but wouldn't even try to calculate these costs in joules. Is this an example of disempowerment (no pun intended)? Food for thought? Andrewa 18:55, 19 October 2005 (UTC)

It's an example of why decimal time would be a good idea! If there were 100 seconds in a minute and 100 minutes in an hour and ten hours in a day then conversion between watt-hours and joules would be simple power-of-ten multiplication/division. :-) --Ali@gwc.org.uk 12:23, 1 November 2005 (UTC)

[edit] Reasons for the request for help?

Without claiming myself as any kind of expert, what kind of help is needed in here? I noticed that the article got a bit repeating about the non-SI:ness (what a word there) of the unit, but the best I can figure out is comparison between other articles about non-SI units, and a comparison between another energy unit. Maybe that would reveal some directions where to develop this article. Santtus 17:23, 12 December 2005 (UTC)

As a physicist, this page looks fine to me as is. Perhaps engineers would like to add more content? I am going to remove the request for expert help. If someone would like to put it back, they should say why here. Strait 18:04, 12 February 2006 (UTC)

I think this article is quite redundant with the intro section. There's really only about 3 sentences of content before everything is repeated. In the definition section, it repeats the intro, and is also quite redundate. This article could use a wikipedia cleanup. —Preceding unsigned comment added by Ice Ardor (talk • contribs) 23:47, 15 January 2008 (UTC)

[edit] approximate price in United States

I've never paid an electric bill yet, but about how much does a kWh cost?

It depends on where you are. Some info:

8.94 cents/KWh, US avg, Mar 2005; 18.06 (max) Hawaii, 6.08 (min) Idaho.[1]

7.21 cents/kWh, US avg, 2002; 4.26 (min) Kentucky, 13.39 (max) Hawaii.[2]

20 cents/kWh, California, summer 2001.

8.3 cents/kWh, US avg, Jan 1998; family avg 800 kWh/month, $66.40.[3] Shawnc 15:42, 18 February 2006 (UTC)

And in Manitoba, my April electricity bill works out to 6.246 cents Canadian per kwh, all taxes included. The tail block rate for domestic use over 175 kwh/month is 5.780 cents Canadian per kwh. This may be the lowest or 2nd lowest household electrical rate in North America. --Wtshymanski 23:38, 31 July 2006 (UTC)

what is multipliang factor —Preceding unsigned comment added by 59.161.8.136 (talk) 14:10, August 24, 2007 (UTC)

[edit] Convenience of kWh vs Joule

The article states that the kWh "is a convenient unit because the energy usage of a typical home in one month is several hundred kilowatt-hours." Why is that more convenient than the Joule? A few hundred kWh is about 1000 MJ or 1 GJ, which seems just as convenient to me, with the added advantage that it's an SI unit. Or do I misunderstand what is meant here? If so, it could do with a rewrite. DirkvdM 09:40, 31 July 2006 (UTC)

SI units aren't necessarily convenient units. Witness your own edits to your comment above! --Wtshymanski 23:34, 31 July 2006 (UTC)

That's not what this is about. I don't make a claim. The article does. I just question that and say that another unit is not less convenient (well actually, it is simply because it's an SI unit, but that's not the point). I don't get your second sentence. What do you mean by that? DirkvdM 12:42, 1 August 2006 (UTC)

Well, for one, it makes for easier calculation. If you havea 100W bulb runing for 1 hr/day, then in a 30-day month it uses 30*1*100 = 3000 watt-hours, or 3 kilowatt-hours. To calculate in joules, you need an additional factor of 3600 10,800,000 joules, or 10.8 megajoules. As long as you know how many watts an appliance uses, it's easy to calculate watt-hours based on hours of usage. Nik42 06:14, 25 August 2006 (UTC)

The Wh is confusing to many non-technical people. People around me seem to understand kWh as kW/h (as in km/h), and sometimes say "kilowatts per hour", thus interpreting it as a rate of something with respect to time. I'm tired of seeing kWh and related magnitudes misused in newspapers and magazines. Using MJ, the numbers would have the same order of magnitude, and there would not be such problems. [asegura] --150.241.250.3 10:40, 31 October 2007 (UTC)

And MJ is better? How many people can even pronounce joule, let alone know what it is. At least light bulbs say "watts" on them so that people can understand that if you turn on a 100 watt light bulb it uses 100 watts, and if you leave it on for 10 hours that's one kilowatt-hour (100x10=1,000). Using MJ to me is a deliberate obfuscation and should be avoided like the plague. 199.125.109.83 (talk) 06:59, 14 May 2008 (UTC)

At the present time, kW∙h is a bit more convenient than joule, because devices that consume in the vicinity of a kW are the ones that have an obvious effect on electric bills. Similarly, when thinking about electric bills, it is more convenient to think in terms of hours than seconds.

In the future, it is possible that the joule might be universally adopted for all energy measurements, such as the energy in food (instead of calories). If this were to happen, education would be enhanced because measuring all energy in the same unit would provide a strong hint to people (including school children) that all these different phenomena are fundamentally the same thing. --Gerry Ashton (talk) 15:42, 14 May 2008 (UTC)

[edit] kWh/yr - seconds, hours and years

I just put back the bit about kWh/yr using three units of time in one unit. It was removed with the argument that it wouldn't be interresting info, but I think this discussion at the ref desk proves that some explanation is needed. It is a very confusing unit, so it needs a good explanation. As long as it doesn't have an article of its own (which it doesn't require) the explanation should be here. There are already several links to the section from mentions of kWh/yr in other articles. And I have inroduced the term here only recently, so there needs to be a section for it on Wikipedia. I'm just not sure whether that should be here or under watt. DirkvdM 19:09, 3 August 2006 (UTC)

[edit] Milli?

Milli-, kilo-, mega-, giga-, and tera- are the most-used prefixes.

How is milli- a commonly-used prefix? When is milliwatt-hour ever used? That would be the energy used by, e.g., a 100 watt bulb in .036 seconds! I'm taking the milli- out of that list Nik42 06:18, 25 August 2006 (UTC)

[edit] cal/kcal

Why are cal and Calorie equivalent in the conversion table? Isn't a Calorie (capital C) a kcal and not just a (lower case c) calorie? —The preceding unsigned comment was added by 168.150.253.56 (talk) 01:09, 8 May 2007 (UTC).

The confusion probably arises from the Food energy uses of these terms. In the case of foods, diets, etc. 1 Calorie = 1,000 calories = 1 kcal. However, as used correctly in this article, calorie is capitalised merely because it's used in the top row as a heading Suckindiesel 20:51, 8 May 2007 (UTC)

[edit] seconds and hours

Perhaps instead of writing "1W times 3600s." in the very beginning you could clarify that you mean an hour. Suppose you have a 100w output, then, according to that part of the post, you multiply 100 times 3600 which is not the case according to what is written bellow, i.e. for a 100w bulb you do 0.1kW times 10hours...This is misleading.

[edit] Citiations Needed

Hey, this page needs citations! It doesn't have any! —Preceding unsigned comment added by 216.206.44.10 (talk) 19:52, 7 September 2007 (UTC)

[edit] Watt-hour??

Okay, so I consider myself a clever guy, but I am simply baffled...

Could someone explain exactly what a watt-hour is? I understand its w*h and all that good stuff, but its so confusing.

as stated, "a one-watt load (e.g., light bulb) drawing power for one hour"; how does it differ than a number of watts per hour? How can something be defined as power-time? Thanks! --Pbroks13 (talk) 03:38, 7 December 2007 (UTC)

The units should be chosen so that when used in an equation, the mathematical operations will work equally well on the numbers and the units. For example, if we use the equation

E = P·T

where E is energy in watt hours*, P is power in watts, and T is time in hours, we see that the units watts and hours are being multiplied.

The phrase "watts per hour" impies that watts are being divided by hours. This would be appropriate if power was increasing, such a the power needed to air condition a building increases during the morning, as the day gets hotter. Perhaps for a certain building on a certain day, the air conditioning power increased 2000 watts per hour, from zero watts at 8 AM to 10,000 watts at 1 PM.

Note that the watt, being a unit of power, is formed by dividing joules by seconds; a watt is a joule per second. --Gerry Ashton (talk) 20:02, 9 January 2008 (UTC)

[edit] kWh

I recently added this abbreviation, which is widely used throughout the world, citing four diverse sources of usage. This edit refers.

This has been reverted by User:Gerry Ashton with the edit summary "Revert incorrect abbreviation. Correct usage of measurements is a matter of law. Unlike other language, popular mistakes do not become correct through popularity."

First of all, I cannot imagine which 'law' applies in every English-speaking country of the world.

Secondly this is not a 'popular mistake' it is simply common usage as the above edit, and thousands of published documents in newspapers and commercial publications will attest to this.

Thirdly, the background to this discussion is an exchange of views at Wikipedia talk:Manual of Style (dates and numbers). Whilst blundering onto this page on another matter it came to my attention that MOS currently specifically requested editors not use the abbreviation - "When units are combined by multiplication, use a middle dot to separate them (kW·h, not kWh, kW h, kW-h, or kW•h)". Given the ubiqiuity of the kWh's use in the world in general I found this surprising and (perhaps unwisely) became in involved in the discussion. After completing the above edit my last word at MOSNUM was "If for practical reasons that still elude me MOSNUM wishes to use a less common style, so be it, but the article [i.e. watt-hour] should reflect international usage, not exclude information to suit MOS."

In other words, given the ubiqiuity of 'kWh' at the very least it would behoove this article to explain why it is an error of some kind to use it (assuming this is genuinely the case) citing appropriate sources rather than attempting to suppress information. (The article itself uses it for goodness sake!)

There may be a lengthy and complex background to this issue I am unaware of. The comments of others are requested. Ben MacDui^Talk/Walk 20:11, 9 January 2008 (UTC)

I would welcome including information in the article explaining that this usage is contrary to the recommendation of a number of national and international measurement authorities. It would be a bit tricky establishing that the error is widespread, because conducting surveys or counting Google hits is generally considered original research.

This usage creates a few problems:

• In algebra, variables consist of a single character (discounting subscripts and superscripts), so writing variables next to each other without a space unambiguously indicates multiplication.
• Symbols may consist of more that one character, so at the very least, the reader will have to mentally sort through the possible valid unit symbols and decide from context where the omitted multiplication symbol(s) should be inserted. In some cases, there may be more than one valid interpretation, so the reader would have to determine from context which best applies to the situation. For example, kWhm^-2 might mean kilowatt hour per square meter, or kilowatt per square hectometer.
• SI is intended to be uniform in all fields, to maximize understanding by those not familiar with the jargon of a particular field. Thus, accepting poor usage because it is commonplace within a field creates a barrier to outsiders who wish to learn about the field. --Gerry Ashton (talk) 20:32, 9 January 2008 (UTC)

I have no difficulty whatever with a note to the effect that although kWh is widely used it is not recommended by a number of national and international measurement authorities, assuming this is verifiable. However…. I can't agree that "that the error is widespread". I rather think it is true that its usage is widely accepted as standard across a variety of nations and fields of endeavour. It is, at least in the UK the usual form in almost all walks of life. SI's intentions are no doubt worthy, and there may, in some circumstances, be reasons to adopt this usage to avoid ambiguity. 'Kilowatt per square hectometer' is not a measurement which is commonly used in the electricity generating industry for example, and no real confusion arises. (I have seen kWh/m for kilowatt hour per square meter). I am not an engineer, but in my experience neither space nor dot is commonly used in popular or commercial literature here. I had a quick look at some UK academic literature - all that I saw used 'kWh'.

SI may well be intended to be uniform in all fields, and one day its aims may be achieved. Nonetheless, we don't all speak Esperanto just because someone thinks it's a good idea.

Any amendment needs to avoid calling widespread and well-understood usage an 'error'.

Perhaps something along the lines of "The abbreviation kWh is also widely used internationally, although the SI system does not recommend this use."<sundry refs>. Ben MacDui^Talk/Walk 19:10, 10 January 2008 (UTC)

I absolutely reject the notion that the correctness of a unit of measure can be determined by widespread usage in publications. Publications only reflect the final result of unpublished calculations. The units used in those unpublished calculations may be quite complex and unusual, and the calculations are error-prone. Using strictly correct units during those calculations helps prevent errors, and facilitate the checking of those calculations by colleagues. If reference publications, such as Wikipedia, promote incorrect usage, it will encourage newcomers to technical fields to make errors in their calculations.

I also notice that while you want to include "kWh", you don't propose to include "Wh".

Finally, I am not aware of any reliable source we can cite that says "kWh" is widely used. --Gerry Ashton (talk) 19:45, 10 January 2008 (UTC)

May I chip in here? It seems to me that there are two legitimate roles for this article that are relevant here. One is to state the correct symbol for the kilowatt hour (or watt hour), which is kW h (or W h); another is to point out that the reader may find other common abbreviations used (eg kWh). It needs to be established that use of kWh is widespread, but if so, then I think it should be mentioned, including an indication of where one might expect to find it (electricity bills?). Thunderbird2 (talk) 20:03, 10 January 2008 (UTC)

Well if you try The Chicago Manual of Style and the American Physical Society for starters. There were the four now deleted refs I provided [4] including the Danish Wind Energy Association, BusinessDictionary.com, www.world-nuclear.org and the UK's Open University. How many more would you like? Ben MacDui^Talk/Walk 20:24, 10 January 2008 (UTC)

Of the sources suggested by Ben MacDui, the Chicago Manual of Style (I have the outdated 14 ed.) shows "kWh" on page 482, grouped with other "units other than SI units". So that is a citable source proving that "kWh" is in widespread use. The American Physical Society web link is not working for me, so I can't comment. The four sources mentioned earlier were just examples of usage by individual publications, so were unpursuasive that the usage was widespread.

I would suggest a mention in the article indicating that the usage is not recommended by a national measurement authority (NIST) nor by an international standard-setting organization (IEEE), and that if the practice of indicating multiplication of unit symbols by writing them with no intervening half-high dot or space were followed in general, ambiguous unit symbols could result. --Gerry Ashton (talk) 21:44, 10 January 2008 (UTC)

I have added a small caveat about kWh's continuing use in variety of publications. If you want more references for it the are of course many tens of thousands available. As I said at MOSNUM I think the case for 'kw h' is being overstated but I lack the inclination to pursue the matter. I wish you good luck in your crusade to rid the world of this useful but apparently offensive little acronym, although I fear you will have a frustrating time of it. Ben MacDui^Talk/Walk 20:41, 11 January 2008 (UTC)

[edit] Question on kWh from top

kWh is an abbreviation, right? For kilowatthour or kilowatt-hour?
S.

Webster says kilowatt-hour -- Egil

The characters "kWh" is an incorrect symbol; the correct versions are "kW·h" or "kW h". It is short for "kilowatt hour" or "kilowatt-hour". Standard for Use ofthe International System of Units (SI): The Modern Metric System published by IEEE and ASTM in 1997, on page 14, says that when working with spelled-out unit names, the preferred way to show multiplication is by leaving a space between the units, but a hyphen is also acceptable. --Gerry Ashton (talk) 20:44, 9 January 2008 (UTC)

There's a technical sense in which that is correct, if the term were to be used in scientific papers, which it isn't. In common usage, kWh often occurs. It doesn't matter which it means. Andrewa (talk) 01:20, 21 January 2008 (UTC)

[edit] Requested move

[edit] Post-move discussion

The limited discussion discussion above totally fails to take into consideration the simple fact that megawatt-hours, gigawatt-hours, and terawatt-hours are in general use (and common on Wikipedia), and other prefixes also see some use, and redirect to this article, and make more sense if the article is at "watt-hour". It also fails to take into consideration the question of whether or not to use that hyphen. Gene Nygaard (talk) 22:13, 17 February 2008 (UTC)

Megawatt-hours, etc. are not as common though. Everyone gets an electric bill, usually in kilowatt hours, very few people ever hear megawatt-hour, gigawatt-hour etc. 199.125.109.38 (talk) 02:46, 19 March 2008 (UTC)

[edit] Revision by Unfree

User:Unfree made a revision, but I reverted it for a number of reasons.

• I know of no source that suggests omitting the space between kilowatt hour. Also, the presence of the footnote implies Taylor supports this usage, but he does not.

• Although the explaination of the relationship to the SI energy unit may be overly long, it shouldn't be omitted altogether.

• The word "exerting" is more often used with force rather than power. --Gerry Ashton (talk) 00:44, 28 February 2008 (UTC)