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# Help with how much my appliance costs?

• Posts: 153 Forumite
edited 21 January at 11:34PM

At School things are taught in such a way to make things easier for children to understand, at the same time the energy companies have a horrible habit of quoting the energy cost with the energy cost in the wrong way, for example:

Electricity Unit rate:                        29.21 p/kWh

Electricity Standing charge:            42.01 p/day

Gas Unit rate:                                  5.78 p/kWh

Gas Standing charge:                     27.47 p/day

When they should be quoting

Electricity Unit rate:                        0.2921p/kWh

Electricity Standing charge:           0.4201p/day

Gas Unit rate:                                 0.0578p/kWh

Gas Standing charge:                    0.2747p/day

At the same time I think you might have calculated your original rating for the item wrong, most lighting quotes how many Watts they use, for example for the old bulbs we used to have 100W, 60W and 40W as popular bulbs, today we have LED bulbs typically well under 10W.

A string of 100 incandescent Christmas lights are said to be rated at 40W while LED Christmas lights are often quoted at 4w per string.

To calculate the energy usage you need to know the number of hours they are on per day, to get a reality check it may be helpful to look at the usage of an old TV and a new TV.

An old plasma TV that was rated at 300W

In order to convert watts to kilowatts, divide the wattage by 1,000:

300 watts/1000 =  0.3kWh the h means per hour, so if a TV was on 5 hours a day

0.3 kWh x 5 =1.5kWh a day

So to work out the cost per day it would be the 1.5 multiplied by Electricity Unit rate

1.5kWh x 0.2921p/kWh = 0.43815p so for 30 days £13.1445 with energy hogging TV

My TV uses under 30w so

30 watts/1000 = 0.03 kWh

0.03 kWh x 5 = 0.15kWh a day

0.15kWh x 0.2921p/kWh = 0.043815p so for 30 days £1.31445 with modern TV

so for LED Christmas lights if they were rated at 4w quoted online then it would be

4 watts/1000 = 0.004kWh

0.004kWh x 5 =0.02kWh a day

0.02kWh x 0.2921p/kWh = 0.005842p so for 30 days £0.17526 with LED Lights

Translated to your example of 5w and 27p

5 watts/1000 = 0.005kWh

0.005kWh x 5 =0.025kWh a day

0.025kWh x 0.27p/kWh = 0.00675p so for 30 days £0.2025 for your lamp

So I think you are over estimating the cost as I have it at around 20p a month if you use 5 hours a day, even if the lamp was on 24 hours a day

5 watts/1000 = 0.005kWh

0.005kWh x 24 =0.12kWh a day

0.12kWh x 0.27p/kWh = 0.0324p so for 30 days £0.972 with for your lamp 24 hours a day for a month

I do not know what the app is that you are using but it is might be how you are reading the numbers

It says it used 0.16kWh in November which is 0.0432p for the month at 0.27p/kWh

It also says the total for the year is 1.21kWh so 0.3267p for the year.

• Posts: 13,822 Forumite
Thansk @Spoonie_Turtle , I didn't know where to begin trying to untangle all that!
N. Hampshire, he/him. Octopus Go elec & Tracker gas / Shell BB / Lyca mobi. Ripple Kirk Hill member.
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• Posts: 478 Forumite
edited 22 January at 10:23AM

At School things are taught in such a way to make things easier for children to understand, at the same time the energy companies have a horrible habit of quoting the energy cost with the energy cost in the wrong way, for example:

Electricity Unit rate:                        29.21 p/kWh

Electricity Standing charge:            42.01 p/day

Gas Unit rate:                                  5.78 p/kWh

Gas Standing charge:                     27.47 p/day

When they should be quoting

Electricity Unit rate:                        0.2921p/kWh

Electricity Standing charge:           0.4201p/day

Gas Unit rate:                                 0.0578p/kWh

Gas Standing charge:                    0.2747p/day

Not quite, you’ve got yourself a bit mixed up there. The energy company’s figures are correct (and is the same as how children in school presently would be taught).

29.21p/kWh is 29 pence plus 21 hundredths of a penny per Kilowatt-Hour.

0.2921p/kWh is a fraction of a penny i.e. less than 1 pence. The 0 means there are no whole pennies in this number.

Anything that comes before a decimal point is a whole unit of something, and whatever comes after a decimal point is part of one of those whole units.

If a unit of currency ends in “p” whatever comes before the decimal point is the number of whole pennies it costs and anything after the point is just part of one extra penny - 1.5p would be one penny plus half a penny, and 1.25p would be one penny plus a quarter of a penny.

If our unit is in “£” anything that comes before the decimal point is the number of whole pounds and the two digits after the point is the number of whole pennies. Anything after those two digits is a fraction of a penny, as there are only 100 pennies to a pound. So £1.50 is one pound plus 50 pence, £1.05 is one pound plus 5 pence, and £1.005 is one pound plus zero pence plus half a penny.

This means 29.21p is the same as £0.2921, but is not the same as 0.2921p (this amount would be 100 times smaller). Understanding units and decimal places is essential when working out energy costs, as if my electric was charged at 0.2921p/kWh my entire bill for the year might work out to around £6.
Moo…
• Posts: 689 Forumite
QrizB said:
Thansk @Spoonie_Turtle , I didn't know where to begin trying to untangle all that!
It might go some way to explain the username!
• Posts: 603 Forumite
edited 22 January at 10:51AM
This thread is such a hot mess, it's very entertaining watching people coming along saying 'you're wrong!' and then getting it wrong themselves in novel and unexpected ways.

Watts are units of power. Power is rate of energy use (when discussing electricity at least, this definition will do). Joules are the unit of energy. One Watt = one Joule per second.

To calculate how much to charge you, energy companies need to know how much energy you've used over a period of time, not how much power you draw at any one time. Because a Joule is a tiny amount of energy and you'd end up with ludicrously large numbers, the convention is to measure domestic energy use using a different unit. That unit is kiloWatt hours (kWh). If you use energy at a rate of 1,000 Joules per second (1,000 Watts, which equals 1 kiloWatt, kW) for a whole hour, you will have used 1 kWh of energy.

As just explained above, 1kWh of electricity (technically, electrical energy) may cost 29.21p. Another way of expressing 29.21p is £0.2921. These mean the same thing. It doesn't matter that a way to pay the 0.21p doesn't exist (just like it doesn't matter that there's no way to pay the 0.9p due on a litre of petrol at 135.9p per lire). You generally don't buy just one litre of petrol, or just one kWh of electricity. You buy tens, or hundreds, or thousands, and any fractions of a penny, if present, are rounded off.

For sake of argument if you needed to pay for 1,000 kWh of electricity at 29.21p per kWh, this would be calculated as: 1,000 x 29.21 = 29,210p = £292.10.
• Posts: 2,928 Forumite
Watt is the problem?
• Posts: 11,857 Forumite
It's  a good job they don't use bytes/bits for power
🍺 😎 Still grumpy, and No, Cloudflare I am NOT a robot 🤖BUT my responses are now out of my control they are posted via ChatGPT or the latest AI
• Posts: 603 Forumite
edited 22 January at 11:58AM
Here is a phot from the app:

This is a lamp with an LED bulb in it.
Today it has used 0.01 units of electric.

If I pay £0.27 per 1.00 units of electricity, then today it's used £0.27 (27p - surely not as it hasn't used 1.00kwh?) or £0.02 - 2p?
Oh, and to answer OP's question:

Your lamp used 0.01 kWh today. At £0.27 per kWh (27p per kWh), the cost is 0.27p, or £0.0027.

Assuming 0.01 kWh is typical of a day's use of this lamp, at 27p per kWh (prices may vary) you could run it for 370 days (just over a year) before it costs you £1.

I know some people on MSE go the nth degree to save money, but in this case OP is better off staying off the forum and not posting about their LED lamp; their computer will be using far more electricity for them to ask questions about the lamp than the lamp itself is using!

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