So I got into this a bit over the past year, and put a SmartThings socket behind just about everything in the house. Not so much for the cost saving (which will take forever at £29 for each of the SmartThings sockets), but more to understand where the power is being used so that we can run for longer on solar + batteries.

There's a range of devices that consume practically nothing when they are in standby mode, these include:

  - Phone chargers (0 - 1W)
  - Projectors (0 - 1W)
  - TVs (0 - 3W for the ones we have)
  - Laptops (3 - 4W for the ones we have)
  - AV amps e.g. Denon (2W)
  - Coffee Machine e.g. Jura (4W)
  - Printers (0 - 1W)

There's a bunch of low powered devices that stay on all the time

  - Amazon Echo Show (4W)
  - Presumably the Echos without a screen but I haven't tested them

If I turned all of these two groups off in the house when we are not using them then we might save close to the £30/year, but we have a lot of them and it's not worth the effort.

There's some devices that you have to keep running, but will cycle, these are typically fridges and freezers.

  - Pretty much all around 1W sleep
  - 2 year old full height fridge - peaks at 49W for 7 minutes ever 30 mins or so
  - 2 year old full height freezer - peaks at 75W for 10 minutes ever 45 mins or so
  - 1 year old chest freezer - peaks at 76W for 12 minutes every 30 mins or so
  - 10 year old half height fridge - peaks at 66W for 30 minutes ever 120 mins or so
  - 2 year old half height wine fridge - load isn't smooth, spikes and goes back down, average of about 100W for 10 minutes every 60 mins or so
  - 10 year old combined full height fridge and freezer - 110W for 17 mins every 50 mins or so

There's not much you can do about these (well I could remove some) but they need to stay on.

Then there's some things that can be reduced:

  - I usually walk away from my laptop and leave it running. The external monitor goes to sleep, but the laptop itself continues to use 33W when left like this. If I put it to sleep instead it would go close to 0. Assuming that I leave it like this for 12 hours each evening, that's 0.033kW \* 0.22p/kWh \* 365days \* 12hours = £31.80 - with this change alone I can hit the headline figures
  - We have a Virgin Media Box and an XBox One X, I haven't separated their power usage, they both draw in their sleep/standby mode, but together they are using 38W when in standby. Using the formula above, switching them off for 12 hours would save £36.61
  - Lights, yes, they are only 0.5W each for the Philips Hue, but we've 32 of them in the kitchen alone. That's 16W in standby, for say an average of 18 hours a day over the year when they aren't being used. £20.56 for the kitchen lights to be "off".

Problem with these articles are that some older folk in older houses go round switching off the telly rather than using standby on the remote. That's fine, you might save £1 or £2 over the course of the year, but the house is old, the sockets are close to the floor, the risk of you tripping/falling is much higher. It's never worth it to save £1.

Where it does make sense is people who have a few consoles in the house, leaving them in standby mode (particularly the one where it can download updates in the background), or just walking away from their computer and not putting it to sleep properly. Switch it off instead and you'll save the headline figures easily.

(edited for formatting)