Energy Usage Monitoring

Saving energy is an admirable thing to do but, there comes a point of diminishing returns. In order to identify exactly where that point is you really need to monitor how much electricity (and gas) you are using. There are several ways of doing this and these are covered in this article. The key points to note though are:

  • In many modern homes the electrical energy used is often much less than that used in gas (or oil) to heat your home and your hot water. In our current (modern) home we use nearly four times as much energy from gas as we do from electricity.
  • The end goal is to reduce the amount of energy you are using and knowing how much is used every minute isn't necessarily going to help. Don't get too hung up on the numbers!
  • You need to identify the devices using the most energy and find ways to minimise their usage, replace them with something more efficient or eliminate them entirely.
  • Electrical energy used by any device is proportional to both the (average) power rating and the amount of time it is used.
  • Changing your behaviour is just as important as selecting or changing the devices in your home. There is little point in buying the most efficient devices, if you are only going to leave them on when not required!
  • Changing your own behaviour is good but, you need to change the behaviour of everyone in your household to make noticeable improvements.

I'm going to say it again because it really is too easy to get hung up on the numbers and whizzy bits of kit and services that exist to do this stuff. There is a whole industry based around it and it is growing at a huge rate. Having nice fancy graphs for electricity usage over the day, usage over a month, etc. is really not that useful. There is no such thing as a typical day or month. How your usage varies over the course of a year is interesting but, there is no such thing as a typical year either. All you need to do is understand what things in your home are significant in terms of energy usage and change them or change the way you use them.

Household Usage Monitoring

The easiest way to do this is to simply record your electricity and gas meter reading at regular intervals. On the first day of every month would probably be longest gap that would yield useful information. This would allow you to see how you electricity usage varies through the seasons in a year. It would also give you an average usage figure for a whole year. This is useful information when choosing your energy supplier, as many have a two-tier pricing model.

Electricity meters in the UK typically measure in KWh so it is easy to work out how much electricity has been used between meter readings. To put it into context, in our current (4-bed detached) house we use about 4400KWh in a typical year.

Gas meters readings require some conversion to get to a figure in KWh. To calculate how many KWh of gas you have used, take the number of gas units used (if you have an imperial meter, multiply the figure by 2.83), now multiply the gas units used by the calorific value (39.4) and the correction factor (1.022640), and then divide by 3.6. So, for every 1.0 increase on our gas meter reading we are using 31.674 KWh. but, our house averages about 16,500KWh in gas usage over the year. There is much more usage in the winter months as the house is heated by gas.

Monthly gas usage

The above graph shows our average month gas usage (in KWh). The white bars show month usage in the previous year. As you can see, we use much more gas in the winter months. This is because our current house is heated by gas and the central heating is generally turned off from April to October. The residual gas usage is for hot water heating. We can see from this graph that about 40% of our gas usage is for heating water in our home. A solar water heating system would result in significant savings!

The baseline gas usage this year is slightly higher than last year. This small variation is down to the hot water now coming on 30 minutes earlier than it did previously.

More regular readings will give you a chance to spot spikes in your usage. For example an electric heating in the conservatory used during the winter months, or a swimming pool pump used in the summer months.

If you are going to really track your total energy usage, then you need some kind of automated monitoring device. We are currently using an Efergy e2 (see review), which provides energy usage by the hour. The instant usage reading on this device is very useful in identifying what devices in the home are using the most electrical power. You learn to spot which devices are being turned on and off and better appreciate just how much power is being used. Some examples:

  • We have two ovens in our kitchen and the larger one uses over 3KW, the smaller one over 2KW.
  • Our kettle uses 2700W but it is a Philips 'one-cup' kettle that allows us only to boil the water required and thus is actually on for very short periods of time.
  • The tumble dryer uses kilowatts of power and can often be on for 30-40 minutes! It is one device to be avoided as much as possible.
  • The washing machine also uses significant power but is considered an essential item that has to be used as required.
  • The microwave also uses significant power but again is used for short periods of time and is a much more efficient way to heat things than using an oven.
  • The device was a key driver in us replacing the halogen bulbs in our kitchen and bathroom with LED equivalents. The 15 bulbs in our kitchen ceiling previously used 300W of electricity.
  • The gas central heating actually uses little electricity in driving the water pumps.
  • Our large plasma TV uses nearly 300W of electricity.

Monitoring Tools

Meter Readings iOS App

Meters app screenshot
We use an iPhone 5 app to help capture, visualise and analyse our electricty and gas usage. The Meter Readings app is an excellent tool that can provide valuable information. It handles provides both usage numbers and costs by, handling discounts and tiered charging rates.

Imeasure Website

The imeasure website is a free home energy and carbon monitoring service.

Device Monitoring

plug-in monitor
For measuring the power consumption of individual devices, a plug-in power monitor is very useful. As well as providing an instant power usage reading, these devices can monitor power usage over a time period. For a device like a fridge or freezer, which is constantly turning on and off, this is the only way to get an accurate measurement of its average power usage over time.


This is a screen capture from the above app showing gas usage in our current home over the years:

This is a screen capture from the above app showing electricity usage in our current home over the years


This is a screen capture from the above app at the end of 2012, showing gas usage in our current home. We used 16541kWh.

2012 gas usage

This is a screen capture from the above app at the end of 2012, showing electricity usage in our current home. We used 4583kWh.

2012 electricity usage


In 2011 we used 14854kWh of energy from gas and 4390kWh of energy from electricity.


In 2010 we used 18190kWh of energy from gas and 4107kWh of energy from electricity.


In 2010 we used 16567kWh of energy from gas and 4095kWh of energy from electricity.

Saving Money

With a few simple numbers, you can save yourself a lot of money. The first thing you need is a typical annual usage figure for gas and electricity, preferrably in KWh. With these numbers you can visit a energy price comparison site like uSwitch or Money Supermarket. You can immediately see if you are paying too much.

Energy companies make direct comparison as hard as possible by using things like standing charges, tiered charging rates and a baffling set of tariffs, with long and complex names. Comparison sites allow you to see through these confusion techniques and get to the real numbers and costs.

The numbers will allow you to see the variations due to the seasons and work out things like, how much gas is being used for cooking and water heating, against how much is being used for heating. As an example, we turn off our heating through the summer months, so we know that ~40% of our gas usage is for cooking and hot water. You can then experiment with the controller timings to see if you can use less gas to heat water, whilst not impacting it availability when required.

You can also measure electricity usage whilst you are away on holiday, to get a minimum usage figure. From this baseline, you can identify devices and appliances that are costing you the most money.

Reducing Energy Usage

The most cost effective way of saving energy in most homes is simply by better insulation. Temperature sensors inside your home will show how quickly heat is escaping from each room (depends on outside temperature) and better windows, door seals and other things can make big improvements.

Generating Energy

Smart Meters

The next step forward in energy usage monitoring is in networked meters and devices. In the UK there is a Government initiative to get 'Smart Meters' installed into every home. Smart meter take regular readings automatically (so that you don't have to), typically every 30 minutes. The advanatge over the energy monitoring devices you can buy is that these meters capture the numbers that are used to bill you and are not using alternative approaches to measure usage. This means they are much more accurate and are available for electricity, gas and water meters.

Not only do smart meters simplify the billing process but the regular and accurate readings enable better understanding and prediction of demand. The ultimate goal of smart meters though, is to provide information back to devices and to also control devices, so that the demand peaks in the supply networks can be better managed.

Whilst this sounds like a great theory, in practice the UK has decided to use GSM modems as one method for collection of metering data. This begs the question as to how it would work in areas where there is no GSM mobile network coverage. We can't see consumers being forced to have a broadband network connection and data transmission through the national grid is a non-starter.

Another major issue with this approach falls outside of the actual billing for gas, electricity and water used. From an end-consumer perspective, the most savings will be made by changing their behaviour. This can only be achieved if a suitable display is provided in the home, that enables them to see real-time usage and historical data. It is unclear how this will be achieved in the current plans.

And finally, we come to the most controversial aspect of smart metering, which assumes that the energy providers have some form of control path back into the home, to communicate with suitable enabled devices and to manage total consumer demand of energy over the course of each day:

  1. Are consumers going to have the required network connectivity to enable this in their home?
  2. Are consumers going to adopt and possibly pay a premium to have networked and controllable devices in their homes? Would the money not be better spent on making the devices more efficient in the first place. As an example, simply better insulating a fridge will massively reduce its energy consumption.
  3. Having this new interface to allow remote control of the device assumes that it is always on (and thus using some power). Some of the most energy intensive appliances (cookers, kettles, dishwasher, tumble dryers, etc.) are generally switched on when they are needed to do their job. Any remote control capability that delays them in completing their task is going to upset the average consumer.
  4. Will consumer trust energy providers and suppliers to access their home network? If some form of isolated VPN is required, who is going to provide the networking equipment to support this and will consumers be happy with the resulting limited choice of hardware (modems, routers, etc.) that support this and also pay a premium for this functionality?
  5. Will consumers want energy providers interfering with the operation of devices in their home, especially those early adopters who are quite likely to have some form of local power or energy generation in place, in the form of solar cells, solar water heaters, or wind turbines. Generally, these people will be aiming for an 'off-grid' lifestyle and independence from this kind of control.

Oh, and did I mention privacy? Would you be happy for your electricity and gas company to know when you go to work and what time you get back, when the house is occupied and when you have visitors? All of these things can be determined by monitoring energy usage patterns.

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