saving electricity at home

Saving electricity at home is all round a good thing to do. It saves money, it reduces your carbon footprint if you care about that sort of thing, and it cuts down on waste. What’s not to like?

For some reason the subject has been hijacked by two small changes that seem to capture  lots of column-inches but aren’t that effective in the grand scheme of things – changing your lightbulbs and unplugging your phone chargers when not in use. Sorry to rain on the green parade, but these aren’t the chief power hogs in most people’s homes. This is a straightforward engineering problem, one that is best tackled by measurement and the application of science, not mantras.

You need two tools for the job, one temporarily and the other is a nice to have to keep on top of things. It’s all down to Kipling’s serving-men, though we can stick with What, Where and When.

Tool #1 – Appliance consumption meter

This measures the amount of power used by an individual appliance- you plug it into the socket and plug the appliance into the meter’s socket. It’s nice to get one that measures the cumulative power used over a period, because to get an accurate idea of a fridge’s daily use you want to accumulate the consumption over a week and divide by 7. Most people have a different daily lifestyle on the weekend compared to the weekday, so capturing over a week gets information representative of all types of use.

Appliance consumption meter
Appliance consumption meter

Unfortunately you only need this temporarily while you’re in the Identify the Power Hog stage – they’re not horribly expensive but it’s worth trying to borrow one first. These are also not very accurate at low power consumption devices, such as mobile phone chargers. Presumably the stories about unplugging your chargers came from somebody at Greenpeace measuring a charger with something like this and seeing about 50W or so. If I saw a charger using 50W I would reach for a fire extinguisher. A bit of common sense is needed – a charger is about the same size as a old-skool light bulb. If it’s dissipating 50W, it will be getting about as hot as a light bulb, and anybody who has tried to change one of those that has just blown will know they are damned hot. If it were the phone dissipating the 50W rather than the charger I’d still be very afraid….

View the results for loads less than ~50W with suspicion. Fortunately that isn’t really a problem, you are after hunting the big game here, unless you’re already living off-grid. I was an early adopter, so I got taken for a ride when I bought mine for £20, people like Maplin sell these. You’ll get your money back in power saving unless you’re a hermit.

It’s the things that change temperature that are the power hogs. Hit these guys first, and preferably measure their power usage over a week to know what they are costing you.

Everybody knows electric heating is expensive – every kilowatt-hour in the UK costs you between 12 and 20p on a standard domestic rate. Three kilowatts is about the maximum you can draw from a standard UK power socket, and a typical fan heater is about 2kW. Use one of these suckers for 4 hours and the kWh is 2kW x 4 hours = 8kWh, which could set you back £1.60. If you’re a homeowner using electric heating then look at alternatives such as using a woodburning stove – almost any other fuel is cheaper per unit heat.

It’s hard to live without heating and changing the heat source usually demands capital spend. However, two other domestic energy hogs need to be tackled before the light bulbs –

Fridges/Freezers. These bad guys are on all the time, and worse still, their performance tends to deteriorate gradually over time. I had a Zanussi fridge freezer which was a few years old that drew over 4kWh a day, ie 1500 kWh a year. This punk was costing me £210 a year to run (@14p a unit on average). The one I replaced it with is A rated, and uses about 1.7kWh a day, a saving of ~£120 a year. That cost me £230 in October last year, so it has already paid me back about £100 in power costs this year, and by the end of next year I will have broken even. After that I am in extra time – what investment can you get that gives a 50% ROI year on year these days…

Tumble Dryer/Washing Machine

I was of the view that washing machines were power hogs but mine isn’t, it takes less than 1kWh for a wash. That’s pretty much over a cycle at 40deg  and it doesn’t matter how full it is. So fill it, but not so much the washing can’t move.

The tumble dryer, however, is another matter – it takes about 3kWh to dry a load of washing. There’s a free alternative that doesn’t take power, it’s called a washing line 🙂 Unfortunately this is a change in lifestyle, and not one for the better – hanging washing out is a right PITA. At least the weather forecast is better now so you can usually work out whether it’s going to rain and hence if it’s worth doing a wash in the morning.

The cost of using a tumble dryer is only about 40p a go, but it is a regular cost so like any regular cost it adds up over time. It also knackers your clothes, so the actual cost is probably more like 50p a go when that is taken into account.

Immersion Heater

These guys are such power hogs you can’t usually run them off a 13A plug, though that didn’t stop one landlord of mine doing that, and the plug did get mighty warm too. There are three things you can do here: get a timer, use less hot water, lag the tank as much as you can. if you have one it is worth getting a feel for how much it is drawing – even if you have to switch everything else in the house off and read the meter before you go to bed and then in the morning. When I did that I turned mine off and it stays off – I use my gas central heating on water only mode, it’s still cheaper than using one of these infernal devices.

Use a Whole House Monitor to keep Power Usage down

Once you’ve taken these high-power devices out or got them under control/started saving for efficient versions you can then start fiddling about with mobile phone chargers and light bulbs. There’s a nasty tendency for new things to get added to the background drain of your house, particularly it seems if you have children 🙂 That’s where you need a whole-house monitoring device, which clamps around the main live intake wire and sends the whole house usage. Mine is an Efergy monitor (I got rushed for that too, they’re now less than £50)

Efergy whole house monitor
Efergy whole house monitor

These allow you to keep an eye on total consumption. You soon get used to the background usage of your house with the fridge on and off (mine is 0.12kW and 0.04kW respectively). It’s good because before you go to work you take a look and if it says anything else you’ve left something on that doesn’t have to be on. And you get to see if it creeps up for any reason…

See -nary a word about light bulbs. What about them? My maximum wattage was 60W light bulbs, assume two of these are on all the time 6pm to 11:59 pm for half the year. That’s £18. That duff fridge freezer was costing me five times that much. Using a tumble dryer twice a week costs you twice as much. I can’t get excited about sweating the small stuff. Want to save money on lighting without spending a bean? Never underestimate the energy saving potential of the humble light switch set to the off position. Switch the buggers off when you’re not using them, just like your parents and mine did when electricity was more expensive in real terms….

So where did all this fuss get me then?

My power usage, cost and cost per unit
My power usage, cost and cost per unit

The dip in 2005 and the subsequent peak is an artifact of changing provider then. I got all this kit early 2008. One the one hand it is depressing, I’ve sweated hard to get my power bill back to a shade under where it was in 2003.

On the other hand, I’ve more than halved my power consumption, and the reason the bill is the same is because the cost of electricity has gone up more than two times in seven years. Look at the monotonic rise in the cost graph. This is because North Sea Gas is running out, it is because the Pound in falling, it is because there are lots more people in the world wanting a slice of a limited energy pie. I don’t expect it do come down any time real soon. So although in financial terms I’m not going anywhere, it is still worth doing, else I’d have to find another £500 a year. And personally, I’d rather consume that as decent red wine rather than making a donation to EDF’s slush fund…

There is a nasty little wrinkle in this – look at the unit prices charged:

Differential unit pricing hides the standing charge
Differential unit pricing hides the standing charge

A shade under half my usage is charged at higher rate, which is used to hide the quarterly standing charge of about £16, because most electricity consumers are not adult enough to be prepared to see the cost for the provision of service separately.  So it’s hidden as an extra unit cost for the first 240 units. EDF presumably think that nobody can get the quarterly consumption down below 240 kWh. Now I am half way there. If I could get the rest of the way, by taking over some of my demand by alternative means, or by say using a gas fridge, then I could get a much better marginal rate for energy saving 🙂

None of the steps taken so far  is anything that uses my specific knowledge of engineering, it is simply common sense that anybody can do. It means I don’t have to get uptight about my light bulbs or my mobile phone chargers, and indeed I still use incandescent light bulbs and a LED lamp for reading. In the future I may shift my lighting load to LEDs and renewables, more from a resilience/off-grid POV because I expect Britain to suffer power shortages as a result of a lack of capital investment in its generating capacity in the medium term future, and this sort of solution is specific to me. However, it won’t particularly change my power bill because I switch lights off if I am not using them.


18 thoughts on “saving electricity at home”

  1. It’s good to see a post on energy use written by someone who actually knows what a kilowatt-hour is 🙂 Must be the engineering background…

    I’m in broad agreement with your overall thrust here, and would definitely concur on the use of the plug-in power meters. Likewise, I forked out about £20 for mine, but I think it has paid for itself by revealing some figures. I haven’t bothered with the ‘whole house’ equivalent – in a sense I already have one – my electricity meter 😉 I read it weekly (maybe less in the winter when it’s cold out…) and have a dataset going back over 2 years now.

    My annual electricity usage is less than 1000kWh (that’s daily average between 2 and 3kWh) and more than half of that is down to my computer. But then I don’t have a TV, don’t cook or heat with electricity, have all CFL and use the incredibly effective ‘switch off at the wall’ technique on everything not in active use. The only item which is on 24/7 is the fridge – and you’re right, I should keep rechecking its consumption as it ages. When it was new it averaged out as a constant 23W load, so maybe a quarter of my overall use.

    I also think in terms of resilience – I haven’t done it yet, but I will eventually get some PV panels. With my level of usage I shouldn’t need too much, maybe 400-500W.

    As for my carbon footprint, I’m with a renewables-only provider.

    All of which leaves gas doing the donkey-work for my energy needs (actually, tell a lie, I do SOME cooking electrically – I have a microwave and a toaster – but the MW is used maybe once a month and is unplugged at other times). Hot water and CH (DIY wet underfloor) are on a condensing combi, cooker is gas and I use a hob kettle after burning out three electric kettles in two years (the quality is absolute RUBBISH these days, even from once-reliable brands like Morphy Richards).

    My gas consumption is a whopping 5200kWh/year. As you mentioned the devious tariffs that the energy companies use (ie rewarding you for higher usage etc) I’ll share a tip. I recently changed my gas supplier to Ebico – it hasn’t (or won’t…) make a HUGE difference to my bills, but what I liked is that they charge a flat-rate for units, and no standing charge. And this is irrespective of your payment methods, even pre-paid meters get the same rates. This way I know my bills are strictly proprtional to my use, marginal prices are constant and anything I save in consumption, I save in cost.

    I found last year that an extra 4″ of loft insulation reduced my heating load by about 30% during the peak months – even with a colder winter! That has a pay-back of around three years, having crunched the numbers. Again, looked at in terms of ROI it’s a no brainer.

    As it is, my gas and electricity bills combined amount to less than £500 per year now, and there is still room for improvement. The next priority on the resilience front would be a wood-burning stove. There is plenty of free fuel available, and I’ve worked out I’d need less than a tonne per year – I think I could run it off junk-mail alone 🙂

    Solar thermal for hot water could also be done and remove much of the summer load as well, but it would make the plumbing awkward.

    As I’ve done most of the easy/low-cost things already, I’m now looking at higher capital-cost projects with less marginal ROI. But if it increases resilience, then the ROI is more than just the finances – it’s independence, too, which is priceless.


  2. @Macs, you’ve done a damn sight better than me, and there I was all chuffed that I had got my usage down to 2.8 to 4 kWh per day 🙂 Having said that the decommissioning of the defective Zanussi hasn’t gone through a whole year yet, so my graph may improve.

    I still use an electric kettle because I couldn’t convince myself the losses on the hob didn’t balance out the 3x extra cost of electricity, and an electric kettle is a lot faster. I haven’t broken one yet 🙂

    My gas usage is nearly twice yours and I have a wood stove. There again my boiler is old and conventional radiators are used. How are you going to tackle your PV? I am toying with the idea of running a 24 or 48V system for lighting and computers (if I can find a 48V to 19V laptop supply) and an inverter for the central heating pump. I don’t think I could muster enough PV to take over the fridge/freezer, expect perhaps in summer.

    The trouble is all government support for PV has to be installed by an MCS installer. All of a sudden the extra advantage of grants gets sucked into labour costs that I could save by doing DIY, and the anti-islanding requirements of a grid tie inverter clobber the resilience upside 😦


  3. Well, I’ll confess a major part of my lower gas usage is down to being in a bungalow, so the roof is a more significant proportion of heat losses, and that is now very well insulated. Also it’s quite small, only 2 bed.

    I’m very undecided on the best route to implement PV. A few years ago (when, amongst other things, I was installing PV and wind systems for a meagre living) I would have leapt on the grid interconnect and FIT now available. But that was back in the days when it was still ‘impossible to do’ according to the utilities 😉

    I’m veering more towards DIY standalone system than the grid-tied idea, as you say, it’s more resilient. And at as high a DC voltage as practicable – 24 or 48Vdc seems sensible. Unfortunately my roof faces E-W with no good clear south-facing mounting points (and also being a bungalow there’s a security question, too…) Looking at my loads a 1kW peak inverter should do, though that would reduce me to the hand mower at least until the lawn is all dug up for spuds 🙂


  4. perhaps the “giant UPS” approach, with generation sized to fit the buildings power requirements rather than expecting feed in tarrifs would be a better approach from a resilience POV – indeed, its simply a modern approach to something the Post Office thought up many decades ago for small rural Telephone Exchanges.

    I learned recently that even electromechanical ones were designed with power saving in mind, and only activated energy-hungry pieces of equipment (such as ringing tone generators) as and when required!

    I’ve also not gone for PV yet due to the reasons ermine mentioned – I’m also not one of those “free market conquers all” types I’m suspicious about government plans as they can always change (ironically its often business/trade backed lobby groups who seem to try and get regulations put in place to discourage DIY!)


  5. @Macs, aha, heating fewer rooms has got to be the ultimate energy conservation move!

    @Alex The nice thing about the UPS is the inbuilt transfer switch. An issue with going standalone is the thorny problem of batteries. To deal with the fridge needs about 30Ah @ 48V or maybe double that if I want my batteries to last any reasonable time. The UPS is nice as I could detect battery voltage dropping and connect mains to the input using the UPS as a transfer switch. That way I could build the PV install up gradually.

    Curious with the RT generators – one ones I saw were rotary multiphase motor/generators. I wouldn’t have though they could spark one of those up quickly enough, or are you talking crossbar not Strowger 😉


  6. This is great thank you: I managed to get a free meter from Eon a few weeks ago and although I’ve only done a basic ‘look how much this uses’ test I now understand what I’m doing a little more.

    So far it has made me cook four meals at a time in the oven and boil the kettle less so we’ll see what further reductions I can make.


  7. Nice article and very much echoing my own thoughts. I agree that the hype about CFLs is overdone. They have their uses but they are not a panacea. In fact, they can be misused. In my workplace, when we had GLS bulbs everywhere, they were turned off when not required. Now that they have been replaced by CFLs, the lights are left on all the time, because “the more you use them, the more you save”! This is an example of a modern Jevons Effect, which is always going to make energy conservation tougher than it first appears.

    On a personal note, I am currently moving supplier from EDF to Britsh Gas and I should get a free consumption meter in the process, so I look forward to finding exactly how much electricity our appliances are using.

    Looking back over the past year, I find that we have used 3259 kWh of electricity and 24730 kWh of gas, a total of 27989 which, rounding up, averages to an energy usage of 77 kWh per day or a mean power consuption of about 3.2 kW. I am not sure if this is good or bad for a family of four, but most of the low hanging fruit of energy saving in our Victorian terrace has been picked. I have found that there are only so many tops that women are willing to wear simultaneously.

    There is probably some more insulation I can do, but, having spent a small fortune on superbly insulated windows in the past and then moved house, I am generally skeptical about large capital expenditure on energy reduction. -SG


  8. using the UPS as a transfer switch seems like a good’un – most can be linked into Linux via NUT (network UPS tools), of course I expect you would use the low power embedded Linux computers now appearing (one even fits into a transformer enclosure with mains plug!)

    Conrad even do a blue LED pygmy lamp to mount on the rack for the “power alarm” 🙂

    have you managed to find reasonable priced 48V inverters?

    as for the power saving Strowger kit the full details of it are unfortunately buried in the archives of another mailing list I frequent but I am fairly certain it did only switch the RT generator on the first call, and there was a timer so if no further calls were placed within a few minutes it got spun down again.

    it was in small rural UAXs they did this and the ringing generators I saw looked no larger than a small grinding wheel (as compared to a massive one in a group switching centre) – I expect at worst case might have meant a slightly wonky dialling tone for a second or two but would have gone unnoticed…


  9. I’ll have to do the defence for CFLs by the looks of it – when they were the ‘new kid on the block’ and used to cost £15 a shot I did the maths. Given the lifespan (about 8-10x that of an incandescent) and the lower consumption (20-30% for equivalent light), even at those ‘early adopter’ prices I worked out that on a life-time basis, the return was way better than putting the money in the Building Society – and this was back when you needed more than one finger to count the interest rates.

    @Salis Grano – this silly idea that ‘the more you use, the more you save’ is NOT the fault of CFLs. You clearly have some messed-up-in-the-head management (I know, I know – what other type is there? 😉 )

    As for your 77kWh mean daily consumption, I’d say that is huge – it exceeds my PEAK winter consumption, but then I’m a single person and don’t have to chase teenagers every time they leave a light on or take three-hour long showers any more 🙂


  10. @Macs, hehehe, you’ve touched a nerve there 🙂 The trouble with CFLs is their poor service life. I have one on each landing, and one for the kitchen light. These guys are troopers, and last well.

    I’ve had to change several others, which failed in short times of a year to two years. On autopsy what fails are the pass transistors on the switch-mode in the base, they are obviousy not man enough for the job.

    Now at sub 99p @ Tesco they probably still cost in, but reliable they’re not IMO!

    @Laura Great that Eon are sending these out free now, it is a more constructive use that showering their customers with CFLs to meet their energy-saving requirements. Go for those big items first, and coooling equipment. A desktop PC can also be a surprising power hog – mine uses about 120W. Some have a significant draw even when off.

    @SG that’s a truly awesome gas usage. My gas & electricity bills are about equal in cost, so my gas usage in kWh is 3x electricity, for a total of ~12000kWh p.a or 32kWh/day, about half of yours. I think kids aren’t always the most energy-conscious members of a household, but they tend to be a hit on electricity usage. It looks like the area to tackle for you is gas consumption. I heat all water, central heating and cook with gas and my boiler is more than 15 years old.

    @Alex – I’m an analogue technology man, I’d monitor battery voltage with a comparator and trip on the mains apply to the input with a relay when the battery voltage falls to whatever the minimum spec is for 50% full batteries. Perhaps use a PIC micro to lockout the restart until the PV system has charged the batteries, and stop the UPS charging them from the mains. I was going to look on ebay for a used 48V UPS.


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