Efergy e2 Wireless Electricity Monitor

Efergy e2

The Efergy e2 wireless electricity meter.

A while ago I reviewed a previous Efergy wireless electricity meter and commented on its usefulness, but noted that the unit wasn’t very accurate – it was about 25% in error when compared with my domestic electricity meter. In order to find that out,  I had to read the daily total of units used off the screen of the unit, and plot the data on a spreadsheet and then compare it with the domestic electricity meter over a period of many months. Not many people can be bothered with that type of kerfuffle.

But the device was still useful. Occasionally I would look at the amount of electricity being used in the house, and then walk around switching things on and off and see how much the consumption changed. However, the unit could only really detect changes in consumption of about 10 watts and so the readout could be a little bit noisy, but it was still useful.

A couple of months ago I was contacted by Efergy who asked me if I would like to test their new wireless unit, the Efergy e2. This one should be very accurate because it works by piggy-backing on the domestic electricity meter: simply measures the flashes of light that the meter produces for every one thousandth of a kilowatt hour (an electricity unit) that it uses. Additionally the unit connects to a PC or Mac and data can be downloaded to allow the user to monitor consumption trends over time. It sounded fantastic: accurate and convenient. I happily agreed to review the unit and Efergy kindly sent me one – free of charge! I always knew writing this blog would pay off one day!


The basic setup of the unit was easy – and I was quickly monitoring electricity consumption. However, the software installation was not so straightforward. Installation on my iMac was ridiculous, requiring installation of 3 separate programmes and then a re-start. And after all that, it still didn’t work. Efergy really need another way to do this. Installation on PC was a little more straightforward requiring only that I downloaded an up-to-date version of the software from their web site.


Efergy Software

The Efergy e-link Software. It has a non-standard interface, quirky controls, the scaling of the graphs is random and there is no way to get at your own data. Click for a larger version.

Once the connection problems were sorted out, I downloaded some data from the unit to the PC. The software allows you to see how your consumption has varied hour-by-hour through the day, or day-by-day through the month. However, the controls are quirky and non-standard: the graph’s scale changes from one day to the next making it difficult to visually compare one day with another; the units it uses to plot the data are -effectively – random numbers; and the writing is so small and written in green on grey so that it is almost unreadable.

However, after instruction from Efergy I did manage to download data to my PC – Ahhh!…At last I felt like I was in control. The software saves the data in an old Excel file format which is easy to open and plot. The graph below shows the number of kWhs used, averaged over a period of 1 hour – effectively the average power consumption – hour by hour for the last month. I could also have just downloaded the total number of kWhs used daily. Why the built-in software can’t plot these graphs is a mystery to me.

This is just the kind of data I love to see. I don’t mind the peaks on this graph – they are the dishwasher and the tumble dryer – but this data tells me that no matter what I do, my house uses around 350 watts of electricity (more than £1/day or £365/year) whether I am at home or not! I will get to the root of that!

Electricity Consumption

Electricity Consumption Click for larger Graph


Aside from reviewing your energy usage, one of the key uses of this type of device is to walk around one’s home and see the effect of switching things on and off – Efergy call this the ‘Energy Now’ function*. The previous model was just about OK at this, but it wasn’t very accurate at low power levels – as I mentioned above the readings fluctuated by a few watts making the useable resolution around 10 watts. But the technology Efergy have employed in this unit is potentially much more accurate. By simply recording the time between pulses from the electricity meter, they could have made an extremely accurate meter with a resolution of around 1 watt. But instead they chose not too – apparently in a bid to extend battery life. IMHO this was a poor decision.

Instead of recording the time between pulses, the unit records ‘How many pulses occur in 30 seconds’. Let me explain. For a typical meter, houshold consumption of 120 W will cause one pulse per 30 seconds. 240 W  will cause two pulses per 30 seconds etc. If you are using say 180 W, then sometimes there will be one pulse in a 30 second period, and sometimes there will be two. This unit will tell you that your electricity usage is oscillating between 120 W and 240 W and you will wonder what is switching on and off. But nothing is. In short the ‘Energy now’ function has measurement resolution of 120 W – around 10 times worse than the previous version of this unit, and functionally useless. Grrrrr…

The idea of piggy-backing on existing metering technology is smart and Efergy tell me that future units will incorporate my suggestion for measuring the time between pulses and so those units will also be very sensitive for monitoring consumption in the ‘Energy now’ mode. Sadly existing units won’t be able to be modified.

And presumably they will eventually make software that doesn’t irritate people and which works on Macs.

The selling point of this unit is the ability to download data to a PC and to look at usage over a long period of time in detail. This is very valuable and personally I would buy it just for this function. When they sort out the ‘Energy Now’ issue this will be a great little unit which I would recommend to anyone.

You can find the Efergy web site here

* It should be ‘power now’ not ‘energy now’, but Efergy say they used this metrological inexactitude in order to communicate more clearly.


2 Responses to “Efergy e2 Wireless Electricity Monitor”

  1. Nestor Patrikios Says:

    Interesting! I will wait for release 3.

  2. stevewaclo Says:

    I’m having difficulty sorting out the kW/kWh issue as well and Efergy really needs to clear this up. As the author points out above, “Energy Now” is indeed a nonsense term because energy (kWH) may only be measured as time passes. kW (power) on the other hand, is instantaneous electrical load and can be measured in snapshots at any given time.

    Thanks for the article and all the best.

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