Standby power - the unseen energy vampire

Simply put, standby power is the amount of power something is using when it's not switched on. One example might be your television. When you turn the television off, it's unlikely you're going to unplug it from the wall. This means that it's going to draw a small amount of power even when it's "off".

If we expand beyond this broad definition though, you could also include power used by things that are on 24/7, even if you use them for a good portion of the day. I would include Wi-Fi routers in this category for example. Most people would leave it on 24 hours a day, but wouldn't be using the Wi-Fi at 3:00 in the morning.

A lot of this usage is likely unnecessary. Terms like "vampire usage" or "phantom usage" appear in the press with scary-sounding numbers to describe how much power wasting. For example, Hydro Quebec estimates that 10% of electricity usage falls into this category 1, while British Gas says that UK households are wasting £147/year on these vampire devices 2.

Given that this could be a significant fraction of my household electricity usage, I wanted to work out how much I was wasting and where it was being wasted. I wanted to see if there were low-hanging fruit for saving power and I wanted to see if the estimates that are all over the press are realistic for my household.

Measuring my standby power usage

To work this out, I needed solid data on household electricity usage in real time.

I began with everything in the house "off". I say "off", and not off, because the point was I wanted to see the standby usage.

What this really meant was that I turned off all the major appliances around the house, fridge off, freezer off (I'll consider these separately later), lights off etc. but with everything else in the background still "on". These background devices included things like Wi-Fi routers, PCs in standby, ovens, microwaves, TVs, smoke alarms, etc. All in standby, or at least as "off" as they would be during normal life.

At this point, I guessed that perhaps I had maybe 20 devices still left drawing power. It turns out it was almost double that, with 38 devices still drawing power.

To work out individual device consumption, I used my smart meter in-house display. I waited for the power usage value to stabilise, then turned off one device "properly", usually by unplugging it but sometimes by turning off the relevant circuit completely if the device was hard wired. The power usage value then dropped and settled after about one minute. I read it again and then repeated the whole process with the next device.

This whole process took less than an hour, including making all the notes and readings, and has definitely saved me money and energy so I consider it well worth doing.

How much standby power and where is it being used?

First, some highlight stats:

  • 38 devices that draw power 24/7
  • Total consumption of these devices was 86 watts i.e. a little over 2 W/device
  • Almost two thirds of the standby power was used by "computing" devices including Wi-Fi, PCs etc.
  • Remainder of power was split between "entertainment", "appliances", and "house" i.e. devices that are hard wired as part of the fabric of the building

86 W continuous usage works out at just over 2 kWh/day (86 * 24 / 1000 = 2.06). This is 750 kWh/year which at the current UK price of 30 p/kWh is just under £230/year. This is a massive amount and needs careful investigation to get it down.

The biggest users

Here's a chart of all the devices using 24/7 standby power in my home:

I can also plot a cumulative graph that shows the increasing fraction used as I add devices to the list. The most power-hungry device uses almost a full quarter of all standby power, with the final few devices contributing absolutely nothing to the measured power demand:

You can see that quite a lot of the devices are using either 1 W or 0 W. These are right down at the lower end of what I can measure with my smart meter display – this has a 1 W resolution. Overall though I'm not too concerned about these devices as collectively they use just 18 W which is less than a quarter of all standby power consumption.

It's clear that the biggest devices are the Network Attached Storage (NAS) device and the computer speakers. These use 31 W between them, more than a third of all standby power, costing £83/year between them.

Lowering standby usage

The speakers were the biggest shock. It turns out that they have basically no difference in power consumption between "off" and on. If I turn up the volume they use a few watts more, but that's it.

I immediately plugged these speakers in through an adaptor plug that cuts the mains power to them completely when the computer is put to sleep. This came for free from my energy provider a long time ago, but similar devices are available to buy now.

Power-saving plug

Although this doesn't save any of the power wasted during regular use, it does save all the power consumed by the speakers when the PC is off or asleep. This is most of the time, so the savings are considerable – probably around £17/year.

The other large power draw is the NAS device. This sits on my home network and stores all my files for access by multiple computers. It has two hard drives in it and when I delved into the settings and logs I realized that these hard drives weren't spinning down. A hard drive that isn't spinning uses about 4-5 W less than a hard drive that's spinning.

After a little tweaking, I now have the hard drives spinning down when idle which is saving another £17-20/year.

Other devices that people say are energy inefficient, like televisions, turned out to be quite efficient. This is likely owing to improvements in energy efficiency standards that are being made into law by governments worldwide.

This investigation has definitely highlighted that there's a considerable saving to be made by carefully investigating standby usage of devices and taking steps to ensure that waste is minimized.

But what about refrigeration?

Refrigeration, including fridges and freezers, is another significant fraction of household electricity usage. It's also used 24/7, but I've not included it in the "standby" power calculations above.

We could argue whether or not this is a valid approach, but I've not done it because it would dwarf the rest of the standby consumption. Also, the approach needed to tackle high use for refrigeration is very different to tackling high usage for standby consumption. Because of this, I've tackled refrigeration power consumption in a separate article.

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