How Simple Arithmetic Saves Power

[know of fence]

Watt is Useful

Most really meaningful and intuitive units in physics describe the relation to time: bit/s, mph, Hz. Yet, not all of these unit names explicitly spell out this wonderful relation and sadly neither does watt. Power measured in watt is in fact energy divided by time, it's that simple. Why - I ask you - have we then still people start vigorously converting kWh to years to dollars, when the capital W conveys all that needs to said already? Whatever the reasons may be, there is a simple calculation that you can do once, right now and astonish people around you when this topic comes up for the rest of your life.

Your Own, Personal Power Coefficient

Once you know what 1 W costs for the duration of a year, you'll never need to convert units again, except when watts handily turn to currency when you multiply W with a simple coefficient (multiplier).

1 year consists of 8766 h.
1 kWh costs about 20 cents (22.8 cents is more like it after tax).
Assume 24/7 use. You can always easily divide this to get your 12h working day or any other usage model.

Q: If you burn 1 W or in other words 8766 Wh/year (8.766 kWh/a), each costing 22.8 cent/kWh, how much does 1 W cost for the duration of a year?
A: 8.766 * 0.228 = 1.998 dollars a year (or €/a)

1 Watt = 2 dollars/year
Amazing!

Calculate your own personal power coefficient by replacing your regional prices and adjusting for any part of 24 hours use. Once you know that your legacy 6W clock radio costs you 12$/a, you'll think twice before you'll leave it plugged in the wall, that's how your personal coefficient saves power, the tried and true method of raising awareness.

So, what is your coefficient?

 

[Fayd]

 

[RavenSEAL]

lOl

 

[know of fence]

It's easy to scoff at this or call it trivial, when it actually isn't.

A. While the calculation "2.5 times 2.5 equals ?" is trivial. Most people could do it using a calculator, a sheet of paper or even in their head. The question how to best calculate something like "2.5 times 2.5" is not trivial at all. Other than the school, or machine method, there may exist some specific trickery, which can expedite calculations, like in this case

2.5 * 2.5 = 2 * (2+1) + 0.25 = 6.25
This method is limited to numbers ending with 5 and only multiplying with themselves, but
there are many other tricks like it.

Basically How to calculate something? and How to calculate something most efficiently? are very different questions.

B. The second problem is that of the watt, watt-hour confusion. While I wrote that watt is useful it actually is a really misguiding unit, which is so confusing that it might as well be called "what" or "w00t". Manufacturers would be better off rating power supplies in horse powers probably. (746 W equals 1 hp)
There really is no good reason why PSU aren't labelled in J/s (1 Joule/second = 1 W), though maybe power hours (kWh) are a more intuitive description for energy/work, very much like man hours.

Anyway the real problem is that when calculating kWh at least once people make the mistake of actually calculating kW/h instead. Energy becomes very cheap as a result. This confusion may even be responsible for the wide spread erroneous belief, that it isn't worth saving power or prevent power leakage. Despite rising prices which are bound to at least double in the coming decades, people actually consume more power on average. http://earthtrends.wri.org/text/energy-resources/variable-574.html

C. 200 bucks potentially saved a year may not be much, but it's also money that pretty much is donated to the Russians, the Arabs, the Texans as well as the most evil and dirty of corporations, responsible for strip mining, oil spills, radioactive waste and Fukushima.

 

[Concillian]

Anyway the real problem is that when calculating kWh at least once people make the mistake of actually calculating kW/h instead. Energy becomes very cheap as result. This error, confusion may even be responsible for the wide spread erroneous belief, that it isn't worth saving power or prevent power leakage. Despite rising prices which are bound to at least double in the coming decades, people actually consume more power on average. http://earthtrends.wri.org/text/energy-resources/variable-574.html

People who have disposable income will dispose of it as they please. In many cases, this means using energy to do things that people without the same amount of disposable income would not use energy to do (automatic dishwashers, entertainment, etc...)

Selling energy efficiency to those uninterested is not an easy sell, and you will find some people will be downright belligerent about it.

I'm fairly energy conscious and generally agree with what you're saying, but in my experience many people will view someone who tries to "spread the word" about energy efficiency akin to a religious zealot who is trying to impose views on someone else.

 

[ctk1981]

 

[Mr. Pedantic]

The watt-hour is not misleading (okay, it is, but less so than the alternative) because power companies charge for energy used. Charging for power rather than energy only makes sense if you're an aluminium refinery say, and you're using energy at a constant rate, all the time. The same is applicable to the computer, TV, etc. Using watts would be all well and good, if they are turned on all the time. But they're not.

If you want to know, my fridge, which is obviously turned on all the time, also has its 'efficiency rating' measured in kWh per year. Because power companies charge by the kWh (because it's a much better system than charging per watt with most usage scenarios) it's what fridge makers use, even though for their appliance it makes more sense for power consumption to be measured by the watt.

 

[natto fire]

I appreciate this thread and hope it does educate someone, but I think the great consumer machine has shown time and time again that it has no time for foresight or simple arithmetic, it is busy creating market bubbles/collapses, exploiting third world countries and the like.

Also, ouch on that rate. It ranges from 5.5 cents to 7.5 cents per kwh here. (yay coal, although the 7.5 cent is supposed to be 100% wind power)

 

[know of fence]

Selling energy efficiency to those uninterested is not an easy sell, and you will find some people will be downright belligerent about it.

Nobody really has an interest of reducing the consumer's energy bill, instead energy efficiency which we see advertised on Apple products or PSUs for instance is often an upsell, which understandably elicits mixed reactions.
Even political efforts to prevent the typical obscurantism surrounding this topic zero in on the rather misleading kWh number, which on top of all is not an SI derived unit, because it has converted seconds to hours. On that note:

The watt-hour is not misleading (okay, it is, but less so than the alternative) because power companies charge for energy used. Charging for power rather than energy only makes sense if you're an aluminium refinery say, and you're using energy at a constant rate, all the time.[...]

The watt average could be used to charge people instead of energy total, or at least be included in the bill. An average is not the same as moment to moment consumption, those two unfortunately could be a source of more confusion, I admit.

An earth citizen consumes 1000 kWh a year, a completely featureless number. But once translated to Watt (on average) by dividing it with 8766 h the result is 114 W and it becomes very relatable.
114 W is in the range of incandescent light bulbs or an idling gaming PC or the power a person generates exercising on any typical fitness machine or leisurely riding a bike.

In a nutshell, to make cost projections it's easier to convert to watts (avg.) and make assumptions about average hours per day used.

Additionally most of the avoidable energy consumption is the result of 24/7 operation or idle, stand-by power leakage anyhow.

Also, ouch on that rate. It ranges from 5.5 cents to 7.5 cents per kwh here. (yay coal, although the 7.5 cent is supposed to be 100% wind power)

So your power coefficient roughly amounts to 8.876*0.055 ≈ 0.49 $/W.
Your tariff is likely to be the smallest of the surprisingly wide US price range.

 

[Mr. Pedantic]

The watt average could be used to charge people instead of energy total, or at least be included in the bill. An average is not the same as moment to moment consumption, those two unfortunately could be a source of more confusion, I admit.

An earth citizen consumes 1000 kWh a year, a completely featureless number. But once translated to Watt (on average) by dividing it with 8766 h the result is 114 W and it becomes very relatable.
114 W is in the range of incandescent light bulbs or an idling gaming PC or the power a person generates exercising on any typical fitness machine or leisurely riding a bike.

In a nutshell, to make cost projections it's easier to convert to watts (avg.) and make assumptions about average hours per day used.

Additionally most of the avoidable energy consumption is the result of 24/7 operation or idle, stand-by power leakage anyhow.

And how do you get that average power consumption? By taking the total energy and dividing by time. Why not just not do this step and make it easier for everyone?

And while we're on the topic of unintuitive units, kWh is hardly the only one that people seem used to. The foot, yard, mile, acre, ounce, pint, pound, gallon...the list goes on and on. At least a kWh tells you exactly what it is.