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Energy Meters Explored

These days, green issues matter, and how much electricity we burn at home is becoming of concern to many - especially those with a house full of gadgets.

Now there are handy and cheap tools to keep an eye on the cost of running home or office appliances and lighting.


Why do I need an energy meter?

These allow you to monitor and calculate the amount and cost of electricity being used. They work by wrapping a sensor around the master lead running into your home's electricity meter, and working out the kilowatts in use.

Efergy Meter

Listen to show 19, where we covered Energy Meters:

Play Show button Download show now button


Energy Monitoring Products:

Here's a list of the leading Energy Meter products that we've been able to find:

Current Cost Envi CC128 Meter

Current Cost Envi CC128 Meter

A great energy meter that displays useful history information on your recent electricity consumption, as well as current KW rate, cost, time and temperature.

The Envi also connects to a PC or Mac, you can track, store and share your power consumption data. We reviewed the Envi in Show 45.

  • You can buy direct from the manufacturer's Amazon Store
  • Or, get one free with the EON Energy Saver tariff (Switch with

See the transcript of our Current Cost Envi Meter Review

Efergy Box

Efergy Energy Saving Meter

This records your home's electricity consumption and converts it into a monetary value, based on the cost price of your electricity. This is recorded by day, week and month, and updates every six seconds, so you can easily see the cost of turning on the TV or making a cup of tea. A great product, which we review later on this page.

See our review of the Efergy below


Owl Electrisave Electricity Monitor Five Stars

Similar to the Efergy we review here, this is a portable, easy to read electricity monitor designed for both use in the home and small office. It shows you how much electricity you are using and the cost. Lacks the ability to cycle through historical data.

Wattson Energy Meter 

Wattson Energy Meter

For the style-conscious, this energy meter offers the same basic energy monitoring features of the others mentioned here. It measures 117 x 105 x 56 mm and has a USB socket for connection to your PC, with special software to allow you to record and analyse your energy usage on a PC.

Energy Meter Socket 

Plug-in Energy Monitor

Plugs into a spare mains socket, and lets you test how much a piece of equipment is eating. Typically, these measure voltage, amps, watts , volt-amps, hertz and power factor.

  • There are four different models of Plug-In Mains Power and Energy Monitors available at Maplin Electronics

We recommend: Owl Energy Monitor - Under £30 (Save £20!). More details Five Stars


Efergy Energy Meter Review

The Efergy meter is a smart electricity meter that lets you see how much electricity you're using, and have used. It also displays how much harmful Co2 you are contributing to the greenhouse effect.

Keen to get to try one of these energy meters, we ordered one from Ethical Superstore. When ordering, there's an option to pay an extra £1, to offset the carbon of delivery, which we endorse. Take a listen to Show 19, where we featured a review of the Efergy Meter.

There are two parts to it - a transmitter that's sited near to your home's electricity meter, and a handy wireless display that shows current and historic use.

The Efergy box contains the meter and transmitter (both are powered by 2 sets of AAA batteries), the sensor, a 12-page set of instructions, some velcro pads, and a free cardboard pencil (nice touch!).

Efergy box contents
Efergy box contents

Installing the Efergy energy meter

The process is pretty straightforward, and took a couple of minutes. You need to go to your home's electricity meter, and clamp the sensor around the outside of the Live home-side cable. There's no cable cutting, unscrewing or anything dangerous involved - you just clamp the sensor around the outside of an existing insulated wire. Most home electricity meters have four wires running into the bottom - two wires to the outside world, and two connected to your indoor wiring - one of these is the Live one - normally the fourth from the left. Here's a shot of ours in situ:

Efergy box contents
Efergy box contents

The wire from the sensor runs to the small transmitter, and can be velcro'ed to somewhere close to the meter.

Installation-wise, that's pretty much it - the transmitter sends a wireless signal to wherever the portable meter is.

On the portable meter, you have to set a small amount of information before things get interesting: It took us about two minutes to set it up. Here's what we had to enter: Time and date, mains voltage (e.g. 230V), tariff information (e.g. 8p per kWh - obtained from your bill or energy provider's site), and an alarm setting (beep if max consumption in kWh is exceeded).

Efergy Meter

The meter has four buttons - a button to switch between live and historical data, left, right and an "Efergy" button that scrolls through the data available. It also has a useful backlight. Here's what the Efergy meter can display:

View Current data:

  • Electricity costs - Cost in £'s and pence of your current utilisation (plus accumulated value over time)
  • Carbon footprint - A display in kgCO2 of your current carbon emissions (plus accumulated value over time)
  • Consumption - in kWh (plus accumulated value over time)
  • Consumption - in kW. This is the interesting one - a real-time look at how much power your house is eating. Turn on the kettle and watch the value rise. Turn out the lights and unplug the telly - and watch the numbers fall.

View Saved data:

  • This particular meter has a built-in memory, and you can review cost in £s, Carbon footprint (kgCO2) and power (kWh) for each day, week and month that the meter's been live

Summary: Efergy Meter

The Efergy Meter is easy to use, easy to install, and very addictive. We're very impressed with this product - it seems very accurate, and not more than a little scary.

After first fitting ours (into our producer's house), we spent a while wandering around the house, seeing how thirsty things are. Washing machines, kettle and microwaves are big culprits, and on the first full day of use, we found he'd used 85p in a day, emissions were 4.07kgCO2, with a power consumption of 9.486kWh. Seeing this real-time information certainly makes you think.

We'd highly recommend this to anyone that cares either about the cost of the electricity they're using, or more importantly, their impact on the environment.

Efergy Meter Availability


Paying too much for your electricity?

The meters featured on this page will show you that you're probably using more electricity than you thought - and how much it's costing. Ways to reduce your bill include using less juice. Switch your washing machine to 30 degrees, switch to low energy light bulbs and turn off unused equipment.

It's also worth looking at ways to pay less for what you use... see:

  • uSwitch - Great bill comparison site for fuel, phone and digital TV. Site accredited by Consumer Focus.
  • EnergyLinx - Make an average saving of £150 with this Energywatch accredited comparison site, and save estimates for 90 days.

Power-saving Sockets

OneClick IntelliPlugGot lots of kit on standby? Another way to save money is to turn off things like printers, speakers, mobile phone charges. The intelliPlug, from OneClick can help. This automatically cuts the power to peripherals when your PC gets turned off. Clever. IntelliPlug is available for around £15 from Ethical Superstore and

There's also the "Bye Bye Standby" product that allows you to switch off standby devices with a simple button-press - also from Ethical Superstore


Listen to our show covering Energy Meters:

Play Show button Download show now button


Energy Meter reliability

Thanks to site visitor David Powell for his opinion on the accuracy of energy meters. Interesting reading...

"Can I please point out that the Efergy meter is anything but accurate. I am an electronics designer heavily involved in low energy products. The meter is simple and that's the problem. It cannot handle anything other than perfect sine wave current which is a big problem its the none sine energy patterns that are the issue. In fact it has a step accuracy of about 18w meaning it sees in multiples of 18w making it fairly useless. In fact the meter defeats it own purpose by indicating that low energy lamps consume about 3 times the rated value because it cannot handle the lamps current curve.

The major issue here is the total misunderstanding by the well meaning commentators over what is power. Many people have been very naughty and showed the generally very high VA values as being actual power consumption - its not at all!!! Example the silly goings on about standby and how it can use up to 50% of active power. Surely people can see how silly this even sounds even if they don't understand the meaning of the values presented. Do they really believe that the giants of manufacturing cannot get their head around using tiny power levels when in sleep monitoring mode but they can design plasma televisions and digital broadcast networks."

Lance Williams comments:

"From practical experience, I have some doubts about the accuracy of power meters when measuring very low wattages, eg below 20 watts. This relates to power meters a few years old, so I wouldn't say that they are current generation. Are you 100% confident that the meters you mention are accurate at the lower power levels you are measuring and do you have any figures from the manufacturers confirming this?"

Martin Pritchard says:

"Regarding the accuracy of the Efergy meter, I've found (by monitoring the supply using a LEM Analyst 3QC power analyser) that mine under-reads by about 10%. Telling the Efergy that the supply voltage was 260V resulted in a more accurate reading. Regardless of the accuracy, however, it does give the householder a rough idea of where the electricity is going, and where savings can be made. For example, my Efergy paid for itself in less than a year by highlighting that my computer's UPS draws around 60 watts even when in "off" mode - it gets switched off at the wall now!"

We also heard from Anthony Horabin:

"I thought I would record my daily usage on my electricity meter compared with the Efergy monitor and found that the Efergy unit reads between 2 and 4 times more usage than I am actually using. I suggest that people, where practicable, just take a daily or weekly reading of their electricity meter to find out how much electricity they are using instead."

... and the counter-argument Angus Hopkins:

Although these are potentially inaccurate, they can have significant benefits in raising energy use awareness and therefore encouraging energy savings. This is done by providing a reference for the energy used in the home. While energy cannot be seen, saving energy is much easier and much more effective when we can understand the relative energy uses of different appliances. For instance, I demonstrated the effectiveness of an energy saving bulb using the Electrisave meter as we have two bedside lamps. One with a standard GLS lamp and the other with a CF lamp. The energy meter, while potentially not totally accurate, recorded a the GLS lamp as requiring 5 times the energy to power it. The meter also demonstrated that a kettle uses enough energy for 400 energy saving bulbs(12W - 3kW) and the electric shower for 900 compact fluorescent lamps.

Introducing simple facts regarding these domestic appliances leads the user to consider the energy demand before using the appliance and therefore encourages conservative use. That is by far the most beneficial use of these meters and this should be indicated."

Got a comment? please post in our Technical Discussion forum


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See also: Our How Many Watts page

Your questions

Q. Can the energy meters also tell if you're electricity meter readings are correct?

No - Energy Meters are intended to give a guide to usage and are not 100% accurate.


Q. I have recently installed solar power on my home.  The system output can be viewed on the Sunnybeam display unit (which is very good).  I also have an energy meter (provided by NPower) which monitors the flow from/to my electricity meter.  The nPower meter cannot distinguish between flow direction to/from the grid and thus it is difficult to whether I am importing power from the grid or exporting to the grid.  Is there an energy meter on the market which will assist me in identifying whether I an drawing energy or exporting it? (Howard)

Q. I have just had solar (PV) cells fitted to my house. Is there an energy meter that will give an accurate exported energy reading? The one I have will only read positive even when the PVs are generating. (Andrew C)

We had this reply from Simon Hudson: "I had the same issue, but solved it with a little help from a colleague. It isn't possible to use these inexpensive meters to show a different reading between energy in and energy out as they use an induction loop to simply measure the current (actually the charge per second) passing through the detector; it measures the magnitude, not the direction. Since mains electricity uses alternating current there is no way to change this. However you can place the detector loop around the cable between your meter and your fuse/rcd switch box. This will measure the amount of electricity you have consumed. Subtract the energy generated, shown by your Sunny Beam and the difference is the amount you pulled from the grid.

To balance it all up I read our meter daily (except when it's cold, wet, I'm hung over, tired or away on business). There is great delight in seeing the meter running backwards, but I've never managed to consume less over a week than I generate - maybe I need to turn some servers off or at least but an Energy Egg."


Other Products:

Got a question on Electricity Meters that we can answer in our next podcast?
Call 020 8133 4567 or send us a message