Save money by tracking your electricity use

How a Current Cost meter can help you reduce those nasty bills

Converting the data

Now we know what the data means, we can start using it to produce graphs that will allow us to interpret it.

As it's provided in a relative way – as in 'this is the electricity used two days ago' – it would be handy to get the exact date and time that the reading was taken. To convert the data we could just write a bit of code, but fortunately we don't need to; Current Cost enthusiast Dale Lane has already done this for us. This handy application is available for free.

His open-source Python script transforms XML data such as <d01>5.2</d01> into a date, time and kWh pair in the format: '15 April 2009 5.2kWh'. Now we need something to feed this absolute data into.

Again, rather than us having to write our own application to handle this, Dale has already taken the process one step further and produced a graphical user interface to produce our graphs for us. All we need to do is feed the data into it direct from the Current Cost meter. Again, the code is open source and is available with some very useful guidance notes. Just download the latest version to get going.

The first time you use Dale's GUI (by unzipping the download and clicking on the '.exe' file) it will ask you where you want to store your data as a '.ccd' file. Next, you need to populate the app with your Current Cost data.

Go to 'Download history' on the toolbar and choose to download the data that you have so far ('Download once | Download via serial port') or remain connected to the serial port for real-time data ('Stay Connected | Download via serial port'). The app will prompt you to let it know which COM port it needs to connect to (you can find out which one it is on your PC by going to 'Device manager' and choosing 'Ports').

The first time that you do this, it can take quite a while to get everything downloaded, depending on how long your Current Cost meter has been collecting data – so this might be a good time to go and put your eco-friendly kettle on. The graphs will appear as soon as the download is complete.

The tabs below the toolbar allow you to toggle between the numerous different views. You can choose to view your data hourly, daily or monthly, and decide whether you want to see the live feed or an average of your daily and monthly electricity use.

Costing the earth

Aside from graphs, the data can be displayed in three ways. To swap between them, change the option ticked in the Data dropdown menu. The 'Display kWh' setting shows your electricity usage in kWh. The 'Display GBP' setting displays how much your electricity is costing you. When you choose this option, the app will prompt you to enter the cost of your electricity in pounds sterling per kWh.

This information will normally be available from your electricity bill. Finally, the 'Display CO2' setting is a simple indication of how many kg of CO2 you are producing with your energy usage. This calculation is based on data from the main electricity suppliers. You'll also notice that there is an option on the Data menu to 'Set personal target'. This lets you tell the app how much you want to spend on electricity.

After you've done this, it will add a horizontal line to your graphs. Stay below that line and you are on target to achieve your goal. If you've only just got your Current Cost meter, the graphs will look a little sparse, but once you've been collecting data for a month or so, the displays quickly let you work out a lot of useful information.

For example, you can see which appliances use the most energy by comparing the time that they were switched on with the energy consumption at that point. You can even work out the repercussions of leaving your appliances on standby instead of switching them off.

For a quick summation of your electricity usage, just click on the Trends tab. If you discover what has caused an unusually high or low reading, you can also annotate your graphs as an aide-memoire – just click on the bar in the graph that you're interested in to add a note. Each graph can be zoomed into or saved as a PNG image file by using the icons at the bottom left of the screen. You can also download the data as a CSV file by clicking on 'Export history'.

Comparing your data

The application has another trick up its sleeve: you can compare your data to that of others and let them see yours. This involves putting your data onto a publicly accessible Google web server. The process requires your Google username and password (you can set one up when you first visit if you don't already have one).

There are clearly some privacy concerns here, but Dale assures us that every effort is being made to keep the data anonymous. Once you're logged in, you can choose friends that you know are participating using the 'Manage your friends' list.

Don't know anyone else with a meter? Not a problem: the 'Manage your groups' option allows you to get data from those in a particular demographic ('two-bedroom houses' for example), allowing a fair comparison between you and them. You can even compare your data to that produced by the National Grid, which can help you to avoid using expensive peaktime electricity.

And there you have it: a simple way to get your electricity usage broken down in real-time, ready to analyse and work out how to reduce it. It's easy to get obsessive about this, though: watch out that you don't end up sitting in the dark, wincing every time someone presses the doorbell.