Power saving myths

Gary_Delaney

My leccy bill is 700 a year for small flat. Too much I think. So I'm trying to cut it. Have already moved to cheapest supplier.

I've read the stuff on boilers and asked some appropriate questions elsewhere.

But is there anywhere that has scientifically backed advice on whether household applicances use power when on stand by. I have recently heard:

1 - appliances use the same power on stand by as in normal use.
2 - applicances use neglible power on stand by, a few pence per year
3 - appliances use neglible power on stand-by if they don't have a motor in but the same as normal if they do. i.e. a telly would be fine to leave on stand by.
4 - that it is irrelevant if the device is on or off. If the plug at the wall is turned on it power is consumed, even if nothing is plugged in.

Clearly most of this nonsense. Any hard facts to be had?

roger56

You cannot apply one simple rule to all electric appliances.
If a device is on standby then it uses electricity even if it's a small amount.
1) is very unlikely.
2) can be true for some appliances
A TV on standby uses very little power compared to when it is switched on.
When switched on it may use 100/200Watts, again depending on the manufacturer.
Here we are talking 6/7pence if left on for 24hours
When on standby it may only use a few Watts. (pence per month)
3) Motors and heaters can use significant amounts of electricity.
A tumbler dryer using 3KW (3000Watts) costs 7/8p per hour to run.
If it has a timer and is on standby then it will probably only use a few Watts (thats pence per month but to state the obvious it's not drying anything!).
4) Not true. If the appliance is switched off no electricity is used (except if it has an indicator light it can use a very small amount - we are taking pence per year!).
If you turn a light off, it's off. No power used.

Some appliances may state current drawn on standby and current drawn when operating. If they do:

Watts = 250V * Current (in Amps)

Example
If your appliance uses 0.1Amps in standby, it uses 250 *.1Watts ie 25W
So it would run for 40hours before using 1KWhr of electricity costing lets say around 2 pence. (that's 40 * 25 which is 1000Watthrs ie 1KWhr)

If that same appliance used 10Amps when operating, then it uses 250 * 10 ie 2500W
So it would only run for around 24minutes before using 1KWhr of electricity.

Lastly, if the current is in mA (thousandths of an Amp) then to get to Amps, multiply mA by 1000.

Hope that helps. Sorry for being a bit technical but that's the way it is.
It's a matter of how the manufacturer chose to design it.

Cardew

Roger56,
Some comments on your post.

You appear to be using off-peak electricity rates 24 hours a day.

"A TV … When switched on it may use 100/200Watts, again depending on the manufacturer. Here we are talking 6/7pence if left on for 24hours".

That would be a consumption of 2.4KwH – 4.8KwH. Even with off-peak electricity(for 8 hours use in the 24 hours) it would cost 14 -28pence for the 24 hours.

"A tumbler dryer using 3KW (3000Watts) costs 7/8p per hour to run"

That is if you have off-peak electricity and run it at night. Standard rates, or day time running, would cost 20+ pence per hour.

I suggest looking at appliances to determine if they state the current drawn(or power consumed) when an appliance is operating is of little value. The figure given is normally at the maximum output and it that does not take into account other factors:

My cooker (with all rings, grill, ovens on) takes 40 amps.(10KwH). With 2 rings and an oven on – all thermostatically controlled and I suspect it consumes 2-3KwH.

My washing machine takes 12 amps(approx 3KwH) yet in a washing cycle taking 90 minutes it can use as little as 0.4KwH.

Fridges and freezers would be even more misleading as they are only running for a small time each day.

I have looked at the standby consumption for my TVs DVD’s etc and typical consumption is 1 watt. Thus it would cost, as you say, approx 50p per year.

Poppy9

Gary

£700 wow. Do you have electric heating. My leccy is £24 per month for a 4 bed semi. I do have gas CH but use a dishwasher, waching machine and tumbler dryer almost daily.

I never leave TV on standby overnight as according to Fire Service it can catch fire.

Murtle

I have a flat and leccie is +/-£35 per month....and that is for heating (storage....) water, washing machine, dishwasher and electric shower....

£700 does seem a lot......

Xbigman

There is one simple rule - if its off its cheapest.

Even stuff that uses minimal amounts more in standby is still using more and it all adds up.
More importantly turning everything off gets you in the habit of being a turner offer, which is 99.9% good.
Regards



X

roger56

Cardew wrote:

Roger56,
Some comments on your post.

You appear to be using off-peak electricity rates 24 hours a day.

"A TV … When switched on it may use 100/200Watts, again depending on the manufacturer. Here we are talking 6/7pence if left on for 24hours".

That would be a consumption of 2.4KwH – 4.8KwH. Even with off-peak electricity(for 8 hours use in the 24 hours) it would cost 14 -28pence for the 24 hours.

"A tumbler dryer using 3KW (3000Watts) costs 7/8p per hour to run"

The point of the post was to put some reasoning into power useage for appliances between ON, standby and OFF and I just chose a rough number for the electricity rate.
Yes the actual costs for the time and rates are applicable and need accounting for for each individuals situation.
Yes the amount of current (and hence power and cost to run) varies with thermostats, motors on or off etc.
As I said you cann't apply one rule for all appliances. Same goes for working out the actual cost of running different appliances, each individuals costs and useage time are different and need to be taken into account.

Midget_Karen

Not true. If the appliance is switched off no electricity is used (except if it has an indicator light it can use a very small amount - we are taking pence per year!).
If you turn a light off, it's off. No power used.

this is not true - some devices use power when "off" unless they are turned off at the wall (yes, i know that's crazy)
I know that because the which? report on printers was talking about a printer where it used more power when "off" than some used when on, so it recommended turning it off at the wall.

Can't work out what it was using power on, myself.....

Cardew

I suppose it is a definition of what is 'on'.

On some laser printers as soon as the main power switch on the machine is 'on' the machine 'warms up' for instant use.

It would be a weird design to do this when the on/off switch is set to 'off' . Why indeed have an on/off switch? Or perhaps that particular machine did not have an on/off switch.

roger56

Midget_Karen

As Cardew said, its down to definitions. The bottom line is there is no absolute industry definition for what is On, standby or off mean as far as the appliance switch is concerned. It's down to the manufacturer.

Turning off at the wall socket/switch will ensure the appliance is really off and drawing no current therefore using no power.

Turning "off" at the appliance doesn't always mean it draws no current.

jjames_3

Midget_Karen wrote:

this is not true - some devices use power when "off" unless they are turned off at the wall (yes, i know that's crazy)

Very true.

Portable radio/stereo systems are bad for this. You switch them to the "off" position, but listen carefully and you'll find that the built-in transformer is still buzzing away like a good'un.

It all depends on how the individual device is wired internally. If the off switch is in series with the PSU, then the connection to the mains is broken and no power is used. If the switch is after the PSU, then it'll continue to use power.

But, of course 99% of devices will use substantially less electricity when in standby than when fully switched on.