The cost of "standby" electrical power

[jackrae]

As an exercise in utility bill reduction, I spent yesterday afternoon identifying the "standby" loads on my house electrical system - in particular my workshop systems.

Although never recommended as good practice by the namby society, I was in the habit of leaving the mains power socket to my lathe's inverter system switched on. Not any more !!

Whilst it might not be representative of all such units, I discovered mine consumed around 44 watts when in the "off" state. This equates to just under £50 per annum in base electricity costs.

Workshop (ex-car) radio powered by a mains transformer unit consumed £19 when "off" (transformer is was left powered on to maintain radio channel selection)

And as an aside my normally never used Technics radio/hifi system also consumed £40 when in the "fully off" state !!

Not a bad days work, £109 per annum saved off my electricity bill

[The Red Baron]

You coud almost buy a small piece of silver solder with that!

[weldsol]

A couple of years ago I got one of those remote swithed multi sockets.
So now when I'm ready to call it a day I can hit one button and that shuts down the standby on my TV, Hifi, Video, DVD, Wii, plus anything else plugged in.

Paul

[chris vine]

Hi Jack,

I was given one of those electricity monitors which has a clamp round the supply cable at the meter.

Our house uses between 300W and 500W when "nothing" is switched on!

Every kitchen appliance with LEDs on it takes 10W, every tv, dvd player takes another 5W to 10W and almost every adaptor takes 5W. Although the modern pulse ones without a transformer do seem to be better.

Then there is the burglar alarm, front door bell transformer, broadband router......

I had a lot of fun switching everything off and trying to get the reading to 0. Or at least 5W for the monitor machine.

I finally succeeded but forgot to turn the fridge back on again. Not very popular!!

Chris.

[weldsol]

Hi Chris
Hope nobody tries one in a hospital
Just think of all the life support systems Ooooop's

[steam4ian]

G'day gentlemen

I may be raining on your parade with this question.

Were your instruments measuring current, volt.amps (VA) or actual watts using true RMS techniques?

Unless the instrument is measuring real watts with a true RMS algorithm the readings are meaningless.

Some devices have a very low power factor when idling, eg the excitation current of a transformer; the real watts is amps x volts x power factor, not the same as amps x volts. BTW clamp on devices which do not also measure voltage will not indicate real watts.

Transformerless devices have a very peaked ac current waveform. Unless the true RMS algorithm is used the current value indicated will be quite wrong, most likely too high. Again the indicated watts will be wrong.

Always compare the watts indicated by the equivalnt heat from say a 40W GLS lamp. Think how hot such a lamp gets when enclosed, can your HiFi system get rid of such heat?

The standby indicator LED will only draw 20ma (max) with a voltage of about 3-4 volts say 4; total watts in LED = 0.08W. If fed from a 12v supply with dropping resistor the total power imput is 0.24W.

Regards
Ian

[houstonceng]

"The standby indicator LED will only draw 20ma (max) with a voltage of about 3-4 volts say 4; total watts in LED = 0.08W. If fed from a 12v supply with dropping resistor the total power imput is 0.24W."

But Ian, you're forgetting that there is a "Stand-by Power Supply Unit" which, in the case of a TV or Hi-Fi with remote control delivers enough power to keep the receiver "live" so that when you press the "On Button", it can respond and turn on the main PSU - powering up the "set".

The biggest problem that most of us have and don't know it is that, often, turning off a Hi-fi or TV at the set, still only turns off the Main PSU but leaves the "Stand-by PSU" live. That's because the "Non-mechanically, but electrically locking On/Off switch" doesn't actually turn the set off.

Otherwise, I totally agree with your True RMS & Watts info.

[Boadicea]

Sorry guys, all this pales into insignificance when taken alongside the money my wife wastes each month.

I just hope you folks have families who will be grateful you spent valuable time saving this money to pass onto them. ;D

[isc]

Things like the vidio recorder, micro wave oven, have clocks as well, Iturn them off at the wall, and don't worry about the time. I don't use the recorder much anyway. TV, off at wall, washing machine like wise. isc

[steam4ian]

G'day Houstonceng.

Thanks for being so agreeable.
I am only trying to get things into perspective. Certainly a few watts are used on standby, it is inevitable and turning off the device will save those watts.

My comment about the heat build up stands. If when on standby the device is not getting warm then heat is not being dissipated and thanks to conservation of energy it is not being used.

If I wanted to make and market a device which showed the purchaser they were saving money I would make a cheap circuit with peak reading ammeter and voltmeter and multiply the two values to indicate watts. The fact that the reading from such a device could be high by a factor of 10 only shows how "wonderful" the device is and what "savings" can be made.

Only true RMS and power factor compensation will give a useful reading, such devices are about but they will be expensive. Compare the cost of a Fluke true RMS meter against that of you average multimeter.

My advice to power savers is to test the "losses" in each standby device by having it as the only thing switched on and watch the disc on the service provider's kWh meter. It may be electromechanical but it does measure true watts. Electronic meters have the smarts to make and integrate true RMS values.

If people want to make savings they should take the little lamp out of the refrigerator. That lamp is on all the time. If you don't believe me open the door quickly and have a look! ;D ;D ;D

Regards
Ian

[Smifffy]

Lol :-)

[Jo]

I have done all the turning off things on stand by and saved £150 a year on my electric bill.

My latest wheeze is to run my workshop by solar power. OK so it only works when the sun shines ( which I know can seem rare in the UK) but thanks the the government's desire to encourage renewable energy it shines sufficiently that they are now subsidising my electric bill by £1500 a year ;D.

Jo

[bobpendleton]

Aug 3, 2011 18:05:09 GMT Jo said:

My latest wheeze is to run my workshop by solar power. OK so it only works when the sun shines ...

Jo

I am now experimenting with PV panels charging my old car battery to power a few 12v LED downlighters. In my case 'only works when the sun shines' is not altogether true since the panels are light driven and produce some power even on dull days. And since the LEDs draw very little power, I can have the lights on when it is dark outside. There's more to be gained, I feel, by repositioning the panels and it is at least theoretically possible to use the battery to drive an inverter. Work in progress! - but there's an answer in there somewhere (I think).

[Boadicea]

Aug 3, 2011 18:05:09 GMT Jo said:

My latest wheeze is to run my workshop by solar power. OK so it only works when the sun shines ( which I know can seem rare in the UK) but thanks the the government's desire to encourage renewable energy it shines sufficiently that they are now subsidising my electric bill by £1500 a year ;D. Jo

Jo, I think it works better when the sun shines - but OK in normal daylight - but you would be the judge. Well done anyway - perhaps you could tell us a little more e.g. what kind of area do you need to generate £1500 per year and are you lucky enough to be facing the right way? What kind of money do the panels cost? What is the difference in output between bright sunlight and a dull day? Would be grateful for ballpark figures.

I think leaving things switched on gives advantages in some cases - you just have to weigh up whether the advantage/convenience is worth the cost for YOU.

On the lighter side, we have an expression in Lincolnshire for saving something as small as the current through an L.E.D. It is called "skinning farts." No offence meant - I did not invent the term, but I think it does apply to some of the points made!

Another tip - do not got out of your way and sit in the queue with engine running to save 5p per gallon of fuel at Tesco - you paid it out in the store, unless you believe in Father Christmas.

[baggo]

I went into this a few years back (2004) and built a quite sophisticated PV rig that powered the house lights reasonably successfully. The cost at the time was very high though for the small output obtained. I did it more as an 'experiment' rather than a way to save money.



The panels cost £350 each (one s/h, one surplus). I built a motor driven mount fitted with an automatic tracker that tracked the sun across the sky during the day and returned the panels to face the east at night, ready for sunrise next day. The panels charged a 12v leisure battery which drove a 300 watt inverter to convert to 240v AC. I also designed a circuit that automatically switched on the inverter when you turned a light on so it didn't have to run continuously. All the house lights are low energy (have been for years) so the power required was low.

The maximum 'power' I ever saw from the two 80 watt panels was about 60 watts total on a very sunny day, nowhere near the rated output of the panels. On a dull day, the output was negligible. In the winter, the output was not enough to keep the battery charged, although it was fine in summer. Eventually, the battery expired and I never replaced it, so the system is no longer used. However, with the huge increase in the cost of electricity now, I think I may resurrect it! The big cost is the storage batteries - the proper deep discharge cells are very expensive.

The modern systems seem to have several kilowatts of panels fastened to house roofs feeding a grid tied inverter that feeds power back into the grid. That's how you reduce your electric bills. There's no storage facility so you can't use any of the power generated during the day once the sun goes down. Also, the panels are only working at maximum efficiency for a couple of hours a day when the panels face the sun. The power drops off drastically when the sun moves to the side of the panels.

There's some doubt whether these systems will ever pay for themselves if you had to fund them yourselves - the cost would be tens of thousands and you can buy a hell of a lot of electric for that. However, some energy companies seem to be offering almost free installation so that might be worth looking at. There's going to be a catch in it somewhere though!

John

[Jo]

Bo: At £14K for my 4KW Sanyo HIT PV system it is not "cheap" and it would never pay for itself with out the government Feed In Tariff (FIT) of 43.3p per unit. With the government feed in tarrif I am expecting to make 16% tax free return on my investment. I am ignoring the 3.1p per unit that I am paid for exporting power on to the grid and assuming that this is going to be used to fund the maintenance over 25 years and I am assuming zero reduction in my actual electricity bill. So total profit? I am expecting to get a clear return of £40K over and above what I could have got if I left the £14K in the bank.

Friends who have the (older technology) multicrystal PV panels up and working are achieving compariable peak outputs as Baggo mentioned of 75% peak power. If you want to see how good these systems are then look up a local installation on:

www.sunnyportal.com/Templates/PublicPagesPlantList.aspx

In theory my HIT PV Panel's should be able to maintain generation in lower light levels but until I have measured and compared my output with my friends over long periods of time I will make no claims.

In the mean time I am going to "make swarf whilst the sunshines".

Jo

[isc]

One place worth looking at for batteries is a fork lift servicing out fit, they change the batteries anually. On one site on google one alternate power person did that, and many years later was still using batteries he bough at scrap price. Another place is hospitals, here they use NIcads about the size of a 24v truck battery. isc

[fred55]

Re the solar, in this part of the world returned electricity is worth more than used electricity, so it makes sense to "make swarf when the sun don't shine". Likewise the washing machine, dishwasher and such. My last bill was minus $55.00. At that rate it will pay for itself in less than a thousand years

[russell]

Sept 25, 2011 8:33:18 GMT fred55 said:

in this part of the world returned electricity is worth more than used electricity,

This seems to be the case in most "developed" countries. It shows the nonsense of government policies when they pay 43 p/unit for electricity that could be generated for 4 or 5 p/unit with very low CO2 output in a nuclear power station.

Russell.

[Jo]

In the UK the energy companies assume (they do not measure) that you use 50% of your home generated power and then pay you for the other 50% the vast sum of 3.1p per unit. So the challenge is to seek to use as much of the generated power at home rather than exporting it and you will still get paid for it.

The 43.3p government FIT is paid on all of the generated power. After 25 years, once the government stops paying the 43.3p per unit generated Feed In Tariff, it will not be economic to have the system repaired if it goes wrong.

Jo