The claim

“IT is an increasingly heavy user of energy – the typical visit to Facebook uses as much energy as boiling a kettle.”
George Osborne, 9 November 2012

The background

Several readers have asked us to adjudicate on the one burning political question that you just can’t ignore this week.

Does it really use as much electricity to catch up with your friends on Facebook as it does to boil a kettle?

That’s what George Osborne asserted in his first big speech on science to the Royal Society.

More than anything else the Chancellor said in the speech – which set out his vision for Britain’s high-tech industries but controversially avoided the thorny topic of onshore wind farms -  this is the burning question that is exercising people on Twitter and internet forums.

Several commentators have claimed that the chancellor was hopelessly wrong - out by an order or magnitude. But we think he’s got it roughly right. Here’s why.

The analysis

This can only be a back-of-envelope effort, but here goes.

Facebook estimated its annual energy costs at 532 million kwh (kilowatt hours) in 2011. About 400 million people were visiting the site every day last year. That’s 146 billion visits per year.

So the energy cost per visit is 532 million divided by 146 billion. That works out at 0.0036kwh. All those zeroes make our eyes hurt so for the sake of convenience we’re going to convert that to a more convenient unit of energy – the kilojoule (kj).

Facebook’s energy consumption is just over 13kj per visit.

How much energy do you and I burn when we check our Facebook page? Well, our energy usage depends on whether we’re using a smartphone, laptop or desk computer, all of which use vastly different amounts of power.

US energy saving guru Michael Bluejay (“Mr Electricity”) has done a lot of the homework for us. He reckons a desk computer and a monitor can guzzle more than 300 watts, while small laptops use less than a tenth of that.

We’re going to accept his estimate of 15 to 60 watts for most laptop computers and use the midpoint of that range – 37.5 watts.

Facebook says the average length of a visit to their site is 23 minutes and 20 seconds. An average laptop running for that length of time will burn 52.6kj.

So if we add Facebook’s costs (just over 13kj) to the end-user’s costs we get nearly 66kj per visit.

But this will undoubtedly be an underestimate. What about all the other equipment in between Facebook HQ and your laptop? Wifi router, local servers etc…

We don’t know how much all this costs and frankly don’t know where to begin. Let’s just remember that our final Facebook figure must be a bit on the low side.

Time for a cuppa

Heating a litre of cold water from room temperature (20C) to boiling point (100C) ought to take about 335kj.

Actually, to be strictly accurate you need to know the exact amount of water, the starting temperature, the specific heat capacity of the material it’s made from, the efficiency of the device and other factors. Others have put the figure at between 240kj to nearly 600kj depending on varying factors.

If Mr Osborne is doing the right thing by the planet and only boiling enough for one cup of tea, say 250ml instead of a litre, this brings the figure down to perhaps 80kj per brew.

The verdict

Our guesstimate is that a Facebook visit uses just under 70kj of energy per visit, and a single cup of tea might need just over 80kj, assuming that you’re on a laptop and you boil as little water as possible.

That’s remarkably close, especially since that first figure is a (cough) conservative one.

In truth, many of the assumptions we’re making are pretty vague, and if you change any of them you could alter the final numbers significantly.

But the chancellor is clearly in the right ballpark, certainly within an order of magnitude of accuracy. Long may it continue.

By Patrick Worrall