Thursday, 5 December 2013

Monitoring Electrical Energy Use / Consumption in the Home....

With electricity prices becoming increasingly expensive, and likely to continue to rise way above inflation, we recently concluded a seven-week long experiment to monitor the energy consumption of most of the electrical appliances in our home.    

The plan was to identify those energy consumers for which there may be scope for a saving, by either changing their pattern of usage or replacing older appliances with more modern and efficient units.  

However, replacing any items would only make economic sense if their total capital costs could be recouped from the predicted savings in their currently-measured operating costs within a period of say five years maximum, or if they should become faulty or breakdown in the future.  We don't intend to discard otherwise serviceable appliances simply because they may not be quite as efficient as the very latest designs on the market.

The five years is actually slightly longer than the period in which I'd normally expect a payback against any such renewal purchase - three years would be nearer the mark.  However, with energy price inflation over the past five years running at around say 8% compared to more 'general' inflation at around 4%, i.e. twice the rate (and no signs of this trend ever coming to an end - see my previous post), then every £1 worth of electricity energy today will actually cost £1.48 in five years time, whereas that unit £1 cost of appliances today will be just £1.22 at the end of the same period.  

To put it another way, cash in the bank in today's money to be spent on future appliances would have been devalued by 18% but cash kept aside for future energy bills will devalue by a whopping 32% after five years.   Therefore, it may make economic sense to bring forward certain renewal purchases because the time they will spend consuming less energy in the future will produce exponentially greater annual savings.

Anyway, back to the testing.  We already had a couple of simple plug-in energy monitors that we'd bought for our micro-generation experiments, and we first established there would be three categories of consumer in the house to be monitored during the experiment :-

  • those users which are continually connected 24 hours per day and consume a relatively constant amount of power, e.g. the CCTV camera power supplies, the CCTV recording equipment and my laptop.  These were monitored over a period of at least three days.
  • those appliances which are continually connected 24 hours per day but tend to operate cyclically, i.e. the fridges and freezers.  These were monitored over a period of at least six days, including one occasion when the freezers were restocked after a regular food shopping trip which we undertake every couple of weeks or so.
  • those consumers which are only ever operated on demand, e.g. the outside lights, TVs, satellite receiver, kettle, microwave, washing machine, the wife's laptop etc.  These were all monitored over a period of at least three days to obtain an average daily consumption, and longer for those which aren't used on a daily basis and therefore there's no real 'regular' pattern of usage.  The exception was the outside low-voltage (LV) lighting, which is on a dusk-to-dawn photosensor and therefore just one day would have been enough to accurately predict annual usage, although we gave it two.

We recognise that some of these plug-in energy monitor aren't particular accurate when operating with very low wattages, but they're better than nothing.

All testing was commenced and concluded at 6.00 pm, convenient since (most of the time) it's approaching the end of my working day, and so the daily figures quoted should accurately represent a full 24 hour period.  

Probably the very largest consumer in the house, the electric cooker, couldn't be monitored at all because we'd have needed a meter with an induction coil which encircles the supply cable, and we don't have such a device.  In addition, the mains lighting fixtures around the home cannot be individually assessed, although every fitting in the house contains a low energy lamp.  

However, we can obtain a general indication of the combined consumption of the devices we can't monitor individually by simply subtracting our forecast annualised consumptions obtained by testing from the last known annual consumption figure as metered by the utility supplier.  This is indicated as 'Untested Consumption' in the results.

So, without further ado, here is a results spreadsheet of the tests, with a forecast annual demand and expenditure associated with each.  

click on the picture for a larger version ....

The costs were based on a tariff of £0.16 per kWhr in today's terms, which is a realistic figure when taking into account VAT and the recent rises in costs of both the metered usage and the standing charge.   At our rate of consumption, the standing charge alone adds £0.01 to the cost of every metered kWhr...

During these tests, we've accounted for almost 85% of our annual billed consumption.  

The results were an eye-opener, especially the energy consumed by my back-up PC which used to run the CCTV DVR (digital video recorder).   This PC is an old tower unit and has been upgraded a couple of times with new motherboards etc, but never with a new power supply unit.

This machine now has an i7 processor and a 500GB hard disk drive (HDD) and, if my laptop should ever fail, it's on standby so I can continue to work although I also now have two standby i3 laptops, having bought a new i5 machine for the business just a couple of months ago.  This older tower PC was used to monitor / record our six CCTV cameras, and excluding the connected monitor that's only turned on periodically, accounted for 1/6 of our total annual energy usage - around 91 W on a continuous basis !  

It simply had to go....

So, before this test regime was even completed, I was on eBay searching for a standalone monitoring and DVR unit for the CCTV.   I found one provided with a 12V/3A transformed power supply, i.e. nominally only up to 36 W power consumption compared to the 91 W we'd recorded for the old PC.  
This new DVR came without a new HDD fitted, at my request - they wanted another £50 for a pre-installed 500GB drive, which is way too much.  I simply formatted the 500GB HDD from the old PC and installed that - I might buy another used HDD for the old PC whenever I get can get a good auction deal on eBay.

I bought this DVR new for £90 delivered.  You can see on the spreadsheet there's a below-the-line entry of a metered test on this new unit - the annual savings are over £100 !   It will pay for itself in less than a year, and the quality is much better than I expected for a low-cost unit.

Another high consumer to look at in the future is the old fridge-freezer, although even if we found a modern one which consumed only 250 kWhr or so, the cost of replacing it will be around £300 and therefore take far too long to payback the £35 per year potential savings to make it an economic proposition, that is at least for as long as the existing one continues to work well.

Our old under-the-counter upright freezer too is also very expensive to run.  We saw a similar new freezer in Argos which claimed an annual consumption of 164 kWhr compared to our current 380 kWhr version, although I'd take any manufacturer's claims with a large pinch of salt.  However, if somewhere near 164 kWhr could actually be achieved then this would save £37 per year at today's energy prices, and so if we could buy this product on sale for around £100 (it's currently £130) then I think it would be worthwhile.  We'll take another look around at the time of the sales in the new year....

The combination of our outside lighting, CCTV power supplies and the new DVR unit still amounts to £104 per year - although it's much better than the £210 it cost before we changed the DVR, there's not much we can realistically do to reduce this sum further - it's the price we pay for security in a semi-rural location.

The television and satellite receiver combined is around £97 per year, but the wife can watch programmes throughout the day 'for free' in her native language via the Hotbird satellite - we don't subscribe to any paid TV services at all except for the compulsory BBC license fee, the biggest con in Christendom...  However, she needs programming to switch the TV off whenever she's out of the living room for long periods.

My laptop consumes £43 per year in electrical energy, but I can hardly complain since this machine provides me with my livelihood and so it's a very small price to pay.  Depreciation on the laptop and the energy costs combined only amount to the fees from a few hours of paid work each year.

On the untested consumption, we need a new electric cooker anyway - the wife broke the outer glass door of the main oven a few months ago, which although is only cosmetic to us (but a very important safety feature if you've young children in the house), it now does look unsightly and since the breakage I've been hunting around for a cost-effective replacement, but haven't found one as yet.  We may even need to shell-out for a brand new cooker, which is around £400 minimum for something of the same size and specification as that we currently have.  If so, we'll make sure it has ceramic hobs and A-ratings for both the main and secondary ovens. 

To conclude, an interesting and informative experiment, and although we consume nearly half-as-much electrical energy again than our next-door neighbours, they're both out all day at work whereas we spend the vast majority of our time at home.

Hopefully, there's still scope for energy savings simply by switching things off when we're not using them.


  1. Interesting analysis. I guess one of the questions you could ask yourself is whether it'd work consolidating the three pieces of refrigeration to two? Surprising that your electric cooking, which presumably is the diff of untested consumption is as low as 2kWh/day. A colleague who lived in a rural location got a combi cooker where the hob was off propane and the oven electric, which might be a way to improve that if you have to change it anyway.

    Those tower PCs are terrible, aren't they - I had one as a music server but switched to a Synology NAS when I discovered the same as you on the power drain. And I have a similar 12V DVR, was originally thinking of this for the farm, it draws about 1A @12V which together with the cams was a bit too much of an ask for a leisure battery. But they're great - you can log in remotely etc.

    Haven't yet found a post on your solar array, that sounds interesting, but I can never yet convince myself that the capex will be recovered in a reasonable time!

    1. Hi. The fridges / freezers would be difficult to consolidate into two units, since one fridge and one freezer are both under-the-counter types, at different ends of the kitchen.

      2 kWhr per day on average for the cooker doesn't seem that low to me. One of the ovens is on for maybe an hour, four or five days per week.

      A propane combi cooker might have been a good alternative - it means fiddling around with changing gas bottles etc, although I do have propane bottles which I bought to fire a small furnace I built years ago.

      Anyway, we bought a new electric cooker last month, on offer from John Lewis...