Energy Saving - A View From My Chair

  • Plantagenet's Avatar
    Level 18
    I better stop doing that then 😮

    A nice tap on the side with a persuader helps,only don’t let the client see 😊
  • retrotecchie's Avatar
    Level 78
    Are you one of those folks like me that still prefer a full-on PC setup for gaming or doing 'real work'?

    Looking at my desk I have two large monitors, powered speakers, a printer and a few other peripherals. A modern computer has soft power control, unlike the old fashioned (up to around 486 or early Pentium) systems with a physical mains switch. In the Good old days, your monitor power cable plugged into the older AT power supplies, so when you physically switched off the computer, it also powered the monitor off physically. These days, LCD monitors just go into soft power down mode...when no signal comes from the graphics card, they go into standby, the power light turns orange, and they sit there waiting for the computer to wake up again.

    You may have a power block which you switch off at the wall, or you may be very conscientious and turn everything off when not in use, but how many people just leave everything on in standby?

    Over the course of a week or so, 'standby' on my IT kit costs me several kWh of wasted energy. Today we trade off convenience against energy savings.

    But, there is a bit of kit available that may help save this 'standby' power.

    Instead of using a conventional four way or six way extension block, you can buy a USB controlled one.

    This has four or six outlets, but only one is live all the time. The 'master', into which you plug your PC. All your other gubbins plugs into the 'slave' sockets which are controlled. A USB plug then connects to the computer. Make sure it is a USB that is powered down when the computer switches off, not a standby powered one.

    When your computer is off, all your slave sockets (monitor, printer, speakers, etc.) are completely switched off at the mains. No wasted standby power.

    When you power up the PC, the USB is powered on and this is then used to control a relay in the power strip, which then powers on everything else.

    I've even added a relay and a USB cable to conventional power strips to make my own. But I only suggest this method if you know what you are doing....safety regulations and so on.

    If you need more 'controlled' outlets, you can connect a conventional strip to one of the slave outputs, and then the strip will also be a slave. Subject obviously to the power handling of the master strip and all your loads.

    In an office with seven people and all their IT gubbins, we measured the results and this reduced office consumption by around 100kWh a year, every year, per person.
    Don't shoot me, I'm only the piano player. I DON'T work for or on behalf of EON.Next, but am willing to try and help if I can. ​​​​​​​Not on mains gas, mobile network or mains drainage. House heated almost entirely by baby dragons.
  • Plantagenet's Avatar
    Level 18
    @Plantagenet

    One of my old mottoes...never trust ANYTHING with springs!
    I tell you what I'll just see if .......
  • retrotecchie's Avatar
    Level 78
    @Plantagenet

    .......​​​​​​​BOINGGGG!!!

    oops!🤬
    Last edited by retrotecchie; 26-11-22 at 16:12.
  • Plantagenet's Avatar
    Level 18
    @Plantagenet

    .......​​​​​​​BOINGGGG!!!

    oops!🤬
    ​​​​​​​I still have nightmares about some of my " episodes "
  • Plantagenet's Avatar
    Level 18
    ​​​​​​​I still have nightmares about some of my " episodes "
    On the phone, "I'm gonna be working late tonight". Dinner in the dog again!
  • retrotecchie's Avatar
    Level 78
    Another tip you often hear...only put as much water in the kettle as you actually intend to use.

    How much is enough? Well, being a bit of a pedant, I took our usual mugs, filled them with cold water to the level I'd make coffee or tea at and poured it into a measuring jug. I know exactly how much water I need to put in, per cup.

    Now, the missus drinks tea, while I'm more of a coffee drinker. Water for your tea needs to be boiling, water for coffee doesn't need to be much hotter than around 95°C.

    So let's look at what happens when you boil the kettle. For the sake of this experiment I'm assuming it's a perfect kettle and doesn't lose much energy to the surroundings. I'm also going to assume that my water comes out of the tap at exactly 10°C and a unit of electricity costs 35p.

    If I fill my kettle to the line, it has a capacity of two litres. Let's call that 2kg of water, as near as makes no odds.

    It takes about 4200 Joules of energy to raise the temperature of a kilo of water by 1°C, so 2kg of water from 10°C to boiling is 2 x 4200 x 90, or 756 kiloJoules.

    That is equivalent to 0.21 kWh or 7.3p to boil a full kettle.

    Now my mugs have a capacity of 300ml, so two cups of tea equals 600ml, or 0.6kg of water.

    My energy is now 0.6 x 4200 x 90, or 226kJ, which is 226.8kJ, 0.063kWh or 2.2p. That's only 30% of the energy, saving 70% of the cost.

    BUT...I could save a tad more energy if I was being really tight.

    I don't want my coffee quite so hot, so I'm going to flip the kettle off before it reaches boiling...a 'guessed' 95°C.

    So, my 0.6kg of water in the kettle now gives me an energy input of 0.6 x 4200 x 85, or 214.2 kJ which works out at 0.0595 kWh or about 2.08p.

    Having made my coffee, I then flip the kettle back on to boil for the wife's tea, only now I'm only heating 0.3kg five degrees.

    0.3 x 4200 x 5 is 6.3kJ which is 0.00175 kWh or 0.06p. Total cost is 2.14p.

    That is a saving of 71% on the cost of fully boiling a kettle. Trifling numbers perhaps, but the missus and I will have a brew at least five times a day. Over a year boiling the full kettle works out at 5 x 365 x 7.3p, or £133.23 a year. £11 a month!

    Boiling just what you need will cost 5 x 365 x 2.2p, or £40.25 a year. £3.35 a month.

    Do it the 'retrotecchie way'? £39.05 a year, or £3.25 a month.

    Saving £130 a year. More when the prices go up again.

    ​​​​​​​Ok, GCSE physics and schoolboy maths, and I have been 'showing my workings', but when you start to drill down into the maths of energy saving, the results can be pretty spectacular.

    And don't be fooled by 'greenwash' for 'eco kettles' or lower powered kettles. Nonsense. A 3kW kettle uses exactly the same energy as a 1.5 kW kettle. It's the same number of Joules you need to get your water hot. The kettle rating is the power in Watts. The energy used is charged and measured by the Watt hour. So you are only drawing half the power...but for twice as long, so the cost and energy use is EXACTLY the same...you're just waiting longer for your cuppa!
    Last edited by retrotecchie; 27-11-22 at 23:43.
  • meldrewreborn's Avatar
    Level 76
    @retrotecchie

    for completeness, how about just boiling the exact amounts in the cups or mugs in the microwave ? Is that more or less expensive?

    ​​​​​​​Answer by 09:00 please.
    Current Eon Next and EDF customer, ex Zog and Symbio. Don't think dual fuel saves money and don't like smart meters. Chronologically Gifted. If I offend let me know by private message, but I’ll continue to express my opinions nonetheless.
  • retrotecchie's Avatar
    Level 78
    @meldrewreborn

    That is a hideously disgusting American habit and should not even be considered by any civilised society.

    But as you ask....

    Can anyone lend me a microwave?!

    The standard rule of thumb to boil a single cup of water in the microwave:

    1. 600 watt will take 4 minutes.
    2. 700 watt takes 3 minutes.
    3. 800 watt takes 2.5 minutes.
    4. 1000 watt takes 2 minutes.
    5. 1200 watt takes 1 minute.


    But the output of the magnetron, in Watts is not the same as electrical energy input. A conventional transformer and magnetron arrangement is roughly 71.3% efficient, and the efficiency of the water heating itself is affected by the container, the position relative to the microwave antenna and whether the oven uses a 'stirrer' or a turntable, has a light inside it and how much power the digital controls or mechanical timer uses.

    So let's assume a net efficiency of, say, 60%. So, changing that table to electrical power rather than cooking power.


    1. 1kW will take 4 minutes. 0.067kWh, or 2.33p
    2. 1.166kW takes 3 minutes. 0.058kWh or 2.04p
    3. 1.333kW takes 2.5 minutes. 0.055kWh or 1.94p
    4. 1.67kW takes 2 minutes. 0.0557kWh or 1.95p
    5. 2kW takes 1 minute. 0.0333kWh or 1.17p


    Roughly double that for two cups, of course....so the kettle still wins hands down, every time.

    If energy saving is your be all and end all then nuking a SINGLE mug of water will be a little cheaper, but because of the way microwaving works, by exciting the polar molecules of water to generate heat, this also removes a large amount of dissolved oxygen (which is usually found in water). Reboiling a kettle multiple times will have the same effect, but a microwave makes the water taste a bit 🩲 in one go.

    Bottom line, nuking water in a popty ping (as we call 'em here in Wales) is more expensive than using a kettle unless you are just making a single cup and your oven is 800W or better (and don't mind the taste).

    Can I go out to play now, sir?
    Last edited by retrotecchie; 28-11-22 at 00:32.