Monitoring Electricity Usage

The government is keen to encourage meters which inform users of their continuing energy consumption. This is easier to do for electricity than for gas, oil or water. There are now several devices which display the total electrical consumption of a house. Since the main meter is not normally easily visible, these units sense the consumption at the meter and use a wireless link to send the information to a portable display. There are now quite a few suppliers of these monitors.

It has been claimed that some users have saved up to 25% on their electricity bills using such devices. However, the amount you save will depend upon how conscientious you are in using the monitor and on taking action to turn off or reduce the consumption of non-essential appliances. If you do not need a permanent monitor in your home, you may consider it would be sensible to share a monitor and its cost with your neighbours.

OWL monitor The Blewbury Energy Initiative has evaluated and can recommend an easy-to-use monitor, which displays current consumption in cost or kWh per hour. This portable wireless monitor in July 2009 sold in July 2009 at £34.95 from www.theowl.com. The Initiative collected enough orders for a bulk purchase in August 2006, and you may be able to borrow one of these.

EFERGY monitor This monitor is similar to the Owl. It can be viewed on www.efergy.com and in July 2009 was about £49.95. It provides over the Owl the useful feature of a record of total consumption by day, week and month. It has not been tested by the Blewbury Energy Initiative.

WATTSON 01 monitor

This monitor is more expensive at around £100. It can be seen on www.diykyoto.com. The display unit is an eye-catching gadget with a bright and clear display of current consumption in watts or the equivalent pounds/year. There are also optional glowing coloured lights indicating the level of current consumption.

The manual claims the display unit can be 30 metres away from the sensor, but in practice the range was only a few metres and did not match the Owl for range.

The display unit holds data on the energy used over each 5-minute period for 28 days, and can load this data into a free computer program, known amusingly as Holmes. Holmes can collect and display data for longer periods, and can graph energy data by month, day, or in 5-minute periods within the day. The data is only held for display by Holmes – it cannot be extracted for analysis, for example by Excel. However, there were a number of problems with getting data into Holmes and its analysis capabilities. Nor does it provide all the functions you might need to control the device. For example, it cannot set the clock in the display or clear the memory, and a separate program to set up the device failed to connect to it.

Overall the Wattson is an attractive product, particularly if you like the idea of coloured lights indicating current consumption. However, the documentation is optimistic and the link to the computer needs more development.

Current Cost monitor

This monitor is provided by several energy suppliers, including Scottish and Southern Energy who give it free of charge to customers who switch to their "Better Plan", which is currently at the same rate as their normal energy tariff. Two members of the Blewbury Energy Initiative are impressed by their Current Cost monitors. The display device keeps a record of past consumption, and can hold data for 3 months. The data on the display unit is retained if there is a power cut. The display unit also provides a data feed over a serial cable to personal computers. The 'official' software to accept and analyse this data is not yet released, but a third-party solution runs on Windows and, with difficulty, on Macs. The monitor is described on www.currentcost.com.

An updated version called the Envi is now available; it adds facilities to monitor single appliances using a sensor that is not yet available.

Discussion

All these energy usage monitors collect similar information which can be useful in minimising energy usage, and all seem able to do this well. The ability to capture a history of consumption on a computer is much less developed, but is also less significant.

The sensors simply clip on to a cable carrying one phase of electricity supply, and detect the current flowing in the cable. (This is normally a red cable about 1 cm across.) Most have provision for accepting several inputs. If there is nowhere where the user can access such a cable, it will be necessary to get a qualified electrician to install the sensor.

Sensors can also in principle measure the energy generated locally, e.g. by solar panels. Here it is even more likely that there is not a readily available single phase wire from the generator suitable to take the sensor clip.

The sensor cannot tell the difference between energy being consumed and energy being exported, so readings are misleading when there is local generation such as solar photovoltaic panels. In addition, the monitor assumes a nominal voltage of 240 volts, so the energy actually used might differ from the estimate because the mains voltage at the time might be 250 or 230 volts. Finally, the phase of the voltage may not match that of the electrical current. This can happen with certain kinds of loads, for example some fluorescent light fittings, and in that case the energy being taken is overestimated.

However in practice these issues are minor, and any of these devices are useful in giving a continuous, readily available and reasonably accurate measurement of energy consumption.

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Recording Energy Usage

The electrical energy monitors described above are useful for determining what is using electrical energy and when excessive consumption is taking place. A complementary approach is to record total consumption at regular intervals. This can include gas consumption as well as electrical consumption, and can provide other ways of analysing the consumption and seeking to reduce it.

The consumption per day when the house is unoccupied shows the total base load, which is likely to be made up by devices such as fridges, answer machines, electric clocks, house alarms and devices on standby. This may include devices that you did not realise were still taking energy such as immersion heaters or pumps.

The difference between summer and winter consumption will be striking for the fuel used for heating. If electricity is not used for heating it will still have a significantly higher consumption in winter because of the extra lighting used. The difference can give an indication of the savings that might be made by more extensive use of low-energy lighting. You may also notice the extra consumption when guests are staying, or gain an understanding on how the heating bill changes with outside temperature.

While it is possible to save meter readings yourself, for example in a spreadsheet, there are also now several services offering to collect your readings centrally and analyse them for you.

Some of the electrical energy monitors average consumption over intervals, and with suitable equipment you can export this data to a central internet site. These include Wattson and Current Cost. The services only record electrical consumption, and are only approximate for the reasons explained above.

The Environmental Change Institute at the University of Oxford runs a free on-line home energy monitoring website at www.imeasure.org.uk, which allows householders to report and track energy use over time. In addition, use of the tool contributes directly to their research in energy and behaviour. This service provides an estimate of costs, but the assumed cost per unit may not match that of your supplier. It also allows you to compare your consumption with others in a group. The data held does not include any personal identification.

First:Utility is an energy supplier committed to providing smart meters which will report electricity consumption over each 30 minutes, and gas consumption daily. Customers can then view this data analysed in various ways. Currently their smart meters are not available in south-east England, but you can still choose First:Utility as your energy supplier. They then provide a financial incentive for you to upload meter readings at regular intervals. These readings can then be analysed in similar ways. A member of the Initiative is trying their service; their current tariff favours fairly heavy users because the rate per unit is low but the standing charges are high.

AlertMe Energy provides an electrical energy monitor linked to the internet, which allows you to monitor your house energy consumption from anywhere. In November 2009 this cost £69 plus £3 a month. This can feed a free application from Google, the Google Powermeter, to analyse the data collected. The Google application will also take information from First:Utility’s smart meters.

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Single-Device Energy Usage

There are several single-socket energy monitors now being sold, priced as low as £10, and we have tested some of them. Typically they plug into a 13 amp mains socket, and provide a 13 amp socket to feed the device being monitored. All the monitors display the instantaneous power being drawn, and seem to work reasonably well in the range from tens of watts up to kilowatts. We hoped they would also be capable of measuring power consumption as low as 1 watt, so that they could indicate which devices consume excessive power when in standby mode or switched off at the device but not at the mains socket. Many electronic appliances consume 6 watts and sometimes much more this way. See Devices on standby. Note that 1 watt taken continuously now costs well over £1 per year. A very desirable extra feature is the ability to totalise the energy used over a period; even better if it retains the information when the device is unplugged in order to avoid having to view the readings in awkward places. However, this requires the device to include batteries.

Members of the Blewbury Energy Initiative bought and tested four models of such monitors, and we give brief summaries of experience so far.

The Maplin device (illustrated at right) was the only one that seemed to be sensitive down to the 1 watt level, and has been used for some useful and sometimes surprising standby measurements. However, one Maplin sample failed, and a replacement adds 6 watts onto all readings. It does not have any facility for totalising the energy.

The Brennenstuhl Electricity Meter (illustrated at left) has been available for some years and provides both the instantaneous energy consumption and its total over time, with battery backup. However, it does not provide accurate readings when consumption is below 10–15watts and is not sensitive at the few watts level. Its display is awkwardly placed for use with mains sockets close to the floor.

The B&Q "Air Force" device looks rather different to the Brennenstuhl, with a more conveniently placed display, but its identical functionality and performance indicates that it is the same device inside. Our sample becomes inaccurate as its battery runs down.

The Proteam monitor (available from Wilkinsons) is the latest to be tried. It seems accurate down to about 5 watts, but is not sensitive below that and so is not suited for tracking down standby consumption of a few watts. It provides total readings in a similar way to the Brennenstuhl and B&Q devices.

Unfortunately, we have not so far found a device that combines the sensitivity of the Maplin with the totalising capability of the Brennenstuhl, B&Q or Proteam. It also seems that their low prices are coupled with suspect robustness.