Saving Energy – The Myth of Vampire Power

There’s nothing like an energy crisis to bring out the urban myths about what’s stealing all of our electricity.  The most prevalent of these is the concept of vampire or phantom power, where devices which are left plugged in or on standby are demonised, with the claim that they consume kiloWattHours of energy, pushing up our bills.  Given that electricity prices in the UK look set to triple this year, that’s a big worry.  However, many of the figures I see being used to support this are decades old, which means that some of the advice being given is misleading or downright wrong.  So I thought it would be a good time to look at exactly how much power our devices actually take, so that people can make informed decisions.

Whilst some of the concerns about vampire power may have been true ten years ago, the electronics industry has devoted a lot of time and effort in reducing the power consumption of consumer products.  That’s not been totally altruistic – much of it has been a response to pressure from the EU and US regulators, who have placed increasingly stringent goals on how much power a product is allowed to consume, particularly when it’s turned off or on standby.  The realty is that most of our devices are never completely turned off, at least not when you press the “OFF” power switch, but they should consume minimal power.  For anyone interested in what this means on a continental scale, the EU produced a very good review back in 2017 about how much power is wasted and what can be done about it.  That has informed more recent regulation, which means that new devices which we buy can be incredibly efficient.

How do you measure energy consumption?

The electrical power that a device consumes is the product of the voltage and the current it takes.  Your energy supplier charges you for the energy, which is the power multiplied by the time it’s being consumed.  It’s measured in kiloWattHours, which is normally abbreviated to kWh.  A few years ago, a kWh was charged at around 12p, which gave a handy rule of thumb that a device that consumed 1W of power would cost around £1 a year if it was on 24 hours a day.  So, if you left a 40W bulb on in the loft when you put away the Christmas decorations, it would have cost you almost £40 by the following Christmas when you opened the loft to discover you’d left it on.  Now that electricity prices are set to rise to 50p per kWh, the annual cost per kWh has risen to £4, so that same mistake would cost you £160.

But back to the main question – should you physically turn things off or unplug your chargers?  I decided to conduct some basic measurements on devices I had around the house to see whether the pundits in the press are telling the truth.  In most cases, they’re not.

To get the figures for energy consumption, I went around the house, gathering up all of the chargers and other devices I could find and measured their actual power consumption, using RMS AC multimeters to measure the voltage and input current.  That let me  calculate show the average standby current, the equivalent annual energy usage and what this would cost if the device were plugged in and turned on for a year (based on a tariff of £0.50 per kWh).

Do Phone Chargers waste Money?

The most common advice that I see is that you should unplug your phone charger once your phone is charged.  Phone chargers have evolved more than most products over the last decade.  They used to be very simple power supplies which just pushed out power to anything connected.  Those are generally relatively large and bulky, as they contain a transformer that reduces mains voltage to a lower voltage for the phone charger.  In the last ten years, they’ve mostly been replaced by a different technology which contains a circuit called a switch-mode power supply.  These are a lot more efficient, so waste far less power.  More importantly, many of these are also intelligent.  They can detect if a phone or tablet is attached and go into a low power mode if nothing is there.  A phone charger supplied with a phone may be even more intelligent, talking to the phone to adjust the way its being charged to make that efficient as possible.

 Average Current (mA)kWh/yearAnnual running cost
Switch-mode chargers0.3 – 1.4 mA0.6 – 2.7£ 0.29 – £ 1.35
Transformer-based chargers11.8 – 16.522.7 – 31.8£ 11.37 – £ 15.90

It’s clear that the older, transformer-based chargers are far less efficient.  The good news is that it’s fairly easy to identify them, as they’re significantly larger, as shown in the picture below.  If you have any of them, turn them off when not in use, but as soon as you get a chance, replace them with a new model.  You can get new, efficient USB chargers on Amazon for less that £5.  If you’ve got a modern one, you’ll save a little bit of money by turning it off when it’s not in use, but you’ll probably save less than £1 a year.

Should I unplug my laptop charger?

Laptop chargers have followed a similar progression, although they moved to switch-mode power supplies earlier than phone chargers.  All of the chargers I could find, even some old ones, were relatively low power, with the most modern one, which uses a Type-C USB connector, the lowest of them all.  The USB connection allows the laptop (or phone, or tablet) to talk to the charger, adjusting the charging rate and moving the charger to a very low-power standby mode once the laptop is fully charged.  The older ones, which just have a two-pin or circular connector, generally don’t have that level of sophistication, but are still remarkably efficient.

 Average Current (mA)kWh/yearAnnual running cost
Two-pin connector0.5 – 5.0 mA1.0 – 10.0£ 0.48 – £ 4.82
Type C USB connector0.2 mA0.4£ 0.20

This was a smaller sample, but it shows that you don’t gain much be turning your laptop power supply off.  I’m not a Mac user, so the figures are all for Windows based laptops, but I’d expect Apple to perform very well.

Are sockets with USB outlets efficient?

I love the convenience of mains sockets with integrated USB outlets.  But I’d never thought about whether they were power efficient.  As it’s not possible to turn the USB sockets off, I thought I ought to check, so I whipped a couple off the wall and tested them as well. 

To my surprise they were remarkably good, taking only half a milliamp, equivalent to £ 0.50 a year.  As you can’t turn them off, that’s reassuring.  If you need to replace any mains sockets, they are definitely worth considering.

Should I turn my Wi-Fi router off overnight?

This is a far more interesting question.  For almost every other device, there’s no harm in turning it off or unplugging it, even if it’s taking almost no power.  However, more and more devices in our homes use the Wi-Fi signals for remote control or monitoring, so the router is probably doing something for more of the day than most people expect.  Depending on what you own, it’s probably being used for your phone calls, video and music streaming, as well as supporting smart doorbells, smart thermostats and burglar alarms.  If you have any of these, you probably want to leave your router on all of the time.

There is also a practical reason for leaving it on, which is that modern Wi-Fi routers constantly monitor your broadband connection to the local exchange, adjusting the way they work to maximise your throughput.  Turning them off each night will affect that optimisation, which may mean that upload and download speeds may suffer for some of the following day.  In theory, that could affect the power consumption when you turn them back on each day.  You’ll probably still save money if you turn it off, but it may not be as much as you expect. 

Determining how big that effect is would require a lot more investigation, so I’ve just looked at the Wi-Fi access points I had lying around and compared their static power consumption when they are on.  As I’ve only got a couple, I added in the published power consumption for some popular models, taking the information from the manufacturer’s data sheets.

 PowerkWh/yearAnnual running cost
Wi-Fi Router5.0 – 14.044 – 123£ 22 – £ 61

Although this looks like a much bigger opportunity for savings, you use your Wi-Fi differently from phone chargers.  If you have any connected devices, like cameras or doorbells, you’ll want to leave it on for most of the day.  The only time it’s likely to be turned off is from the point you go to bed (or stop streaming music or video) until you get up again.  If that’s eight hours, then your saving will only be one third of the annual running cost – from around £7 to £20 a year.

If you change your broadband supplier, you’ll almost certainly get a new Wi-Fi router, which will probably be more efficient.  However, if yours is less than seven or eight years old, it won’t be much better – probably only saving you a few pounds each year.  The one I have is about six years old and is at the lower end of the power consumptions I measured.

Where you may save is getting a Wi-Fi router with whole home coverage.  I ran some checks on separate Wi-Fi extender units, and found they consume between 2 and 5W each, amounting to an annual cost of £9 to £20 each.  So, acquiring a more modern router which gets rid of two extenders might save you £20 – £30 a year.

Coming back to the question of whether you should turn off your Wi-Fi router at night probably depends on the way you use Wi-Fi.  If nobody and no smart products in your household use Wi-Fi for eight hours or more a night, it’s marginally worth doing.  Otherwise, it’s quite an inconvenience for saving around 3p per day.  There are other things you should do first.

How efficient are remote controlled mains sockets and timers?

As a final experiment, I thought I’d test a couple of remote-controlled mains sockets.  These get a lot of positive press as a way of reducing power, as you can use them to turn off appliances which you plug into them, or set up timers to automatically turn devices on and off.  Many now use Wi-Fi, allowing you to control the sockets from an app on your phone.  They all consume power to do that, so the question is whether they use more power than the device they’re turning on and off?

I have half a dozen different ones lying around, which I’ve used for some projects in the past, so I set them up to see how they performed.  As they all have circuitry which needs to be active to receive the controlling radio signals, they all consume power.  Around half of them use Wi-Fi, with the rest using proprietary radio connections.  They were all from little-known brands, but are probably fairly representative.  One surprise was that there wasn’t much difference between the Wi-Fi and proprietary radio versions.  I’d expected the Wi-Fi ones to take more power, but they didn’t.  The other point of note was that most of them consume more power when the socket is turned ON, compared to when it is turned OFF. 

 PowerkWh/yearAnnual running cost
Remote controlled socket (ON)0.7 – 1.06 – 9£ 3.00 – £ 4.40

When the socket is off, the residual power consumption is around half to a third of the ON power.  This means that if you’re using one of these sockets to turn off your phone or laptop charger, you’re wasting money, as the remote-controlled socket costs more to run than your charger.  I’m sure that some remote-controlled sockets are more efficient, but if they are Wi-Fi based, these figures are probably typical.  I did have one outlier, which was a fairly recent Wi-Fi based switch, which consumed over 5W, costing around £22 a year to run, which is certainly not saving anyone any money.

If you’re using timers, either mechanical ones or electronic ones, they take a similar amount of power – around 1 Watt each.  By the time you’ve factored in the cost of purchasing them, you’ve not saved much money.  However, they may be useful from a security viewpoint if what you turn on and off makes your the house look as if it’s occupied. 

What should I turn off to save money?

I’m old enough to remember that my parents always turned everything off when they weren’t using it.  My Dad would normally unplug it as well.  It’s not a bad working principle, but it’s a lot more laborious given the number of devices we have plugged in these days.  He only had the light switches, TV and radio to contend with.

You can turn off your chargers and Wi-Fi, but, as we’ve seen, it won’t save you a vast amount of money.  However, you do need to check your light bulbs.  If you are still using incandescent (filament) or halogen bulbs, like the ones shown below, they are eating up money. 

When the cost of 1 kWh of electricity rises to 50p, which is predicted to happen by the end of 2022, a single 35W halogen bulb running for eight hours a day will cost you over £50 a year.  An old fashioned 100W filament or linear halogen bulb will cost almost £150 a year.  Replacing them with LED bulbs, which work in the same fittings, will cost £5 and £13 respectively.  As new LED bulbs only cost about £2.50 each, you’ll get that expenditure back in a couple of weeks, then carry on saving.  Unlike remembering to turn your charger off every night, you only need to change a lightbulb once to make a lasting saving.

If you’ve got a smart meter, you should have been given an In Home Display that shows your electricity usage, now’s the time to put it to good use.  Find a time during the day when everyone is out and turn everything off in the house.  Ideally, you’ll only have the fridge, Wi-Fi and boiler running, so the energy consumption should be low and stable.  Go around each room and turn the lights on one at a time, including standard lamps.  If the In Home Display registers less than a 10 Watt increase for each bulb that lights up, you’re fine.  If it’s 25 or 50W for each bulb, then you probably need to change that bulb.  There are still a lot of halogen bulbs in spotlights, kitchen lighting, bathrooms and designer lights, all of which can be replaced by LEDs.

If you don’t have an In Home Display, have a look at the bulbs.  If you can see a wire which glows when it’s on, and it feels hot, it probably a halogen or incandescent bulb, so should be changes.  LED light bulb are generally cool.  Doing the bulb check is the most important start to saving electricity costs. 

Other than that, most of the old advice applies.  Have short showers, especially if you use electricity for heating the water, share baths, don’t overfill the kettle, cook vegetables in the microwave and turn things off when they’re not being used.  And don’t worry about vampire power pushing up the bills.  As long as you’ve replaced any old phone chargers, you’ve probably kept the vampires at bay.

If you come across articles warning you about vampire power, screw them up and push them into any cracks around your window frame.  They may serve a useful purpose as a draught excluder, which will reduce your heating bills.  But that’s about their only use.