Chewing through the watts

24 November 2008

Some tweets last night written by Danny Bradbury asking about the energy consumption of mobile phones alerted me to GreenYourPhone, a scheme cooked up by Boulder, Colorado-based Renewable Choice and the electronics chain Best Buy. For $10, you can salve your conscience over the amount of CO2 your talk and text habit produces.

The FAQ on the GreenYourPhone site claims a pair of mobile phones chews through 500kWh (kilowatt-hours) of electricity over a period of two years but is sketchy on where the figure comes from. The page cites Ericsson and Nokia studies but without links. Until Colorado wakes up, it's hard to check. But, looking at the last known studies from Ericsson, I reckon they are using this summary, which claims the amount of CO2 thrown out by the entire mobile network per subscriber per year was 54kg in 2002, falling to 38kg in 2005.

To get to how many kilowatt-hours you need to produce that CO2 you need to divide by around 0.4 if you use the older 54kg figure, which is what I think GreenYourPhone did. This approximates roughly to the mix of coal- and gas-fired power plants found in a country like the US. For every kilowatt-hour of electricity, you produce 0.4kg of CO2. If you use the more up-to-date figure – and efficiency in the network keeps improving, although 3G will never be as power-efficient as GSM – you get to 95kWh.

If you think 125kWh per phone per year sounds a bit steep when the battery stores less than 4Wh – a full charge every day for a year is still only 1.5kWh – the amount does not just over the phones or the energy needed to make them, it accounts for all the equipment that connects them together when you make each and every call.

Even so, GreenYourPhone does fairly well out of the deal. Taking a look at carbon-offset costs, you could cheerfully buy credits for up to five years' worth of calls by shopping around. Offset costs run to between $5 and $30 for a whole metric tonne of CO2. Compare that to $10 for a fifth of that amount. You get a sticker though and "your purchase helps schools" on account of some of them having wind turbines installed.

One big problem with these calculations lies in the number of variables, some of which I've gone into in the latest issue of Engineering & Technology for the magazine's "Green Illusion" special.

With energy, and CO2, analyses, you have two elements in partial conflict. There is the energy used by electronic equipment. Most of the E&T features concentrates on standby power, which was the target of recent US DoE and UK Energy Saving Trust reports. But you can overplay the role of power in use as our attitude to 'disposable' electronics puts a much greater share of the environmental onto production. Even with TVs, if you keep the product running for less than five years as your primary set, manufacturing consumption begins to dominate. With mobile phones, which people replace every two years at least, the equation is dominated by manufacturing.

The big problem with all this is that power consumption in use is fairly easy to estimate. The full life-cycle analysis is tough as, in principle, you have to go right back to the point where someone dug the raw materials out of the ground. You can find many more studies

Even the way in which all the components come together can have a dramatic effect on the energy usage. Take the way that the chip industry moves its stuff around. It takes at least six weeks for a clean, unsullied silicon wafer to make it out of the fab fully populated with transistors. And that is when you really care about getting that wafer done quickly. It takes a few more days to dice up the wafer and stick the chips into plastic packages. The chances are the packaging plant is in a different country to the wafer fab, and half the time is on a different continent. Because it takes so long to get semiconductors through the factory, companies don't like to waste time getting the components from A to B. So, they fly them everywhere.

The average integrated circuit winds up flying about three times before it gets to the factory that will put it in something like an iPod. From than point, it will probably travel by ship because the value/weight ratio is so much lower in finished equipment.

The trouble with all this is that it's easy to get to analysis paralysis and the habit of NGOs and 'green' businesses to over-inflate the impact figures doesn't help. It's fairly clear that the energy consumption of a mobile phone is somewhere in the hundreds of kilowatt-hours range. And it's clear that standby power in consumer electronics is a big problem.

But the Energy Saving Trust last year decided to over-egg the problem by going for the most pessimistic analysis possible, even though this scenario was highly unlikely. When I asked about their use of figures from the UK's Market Transformation Programme, the press officer responded by claiming the release was "just for consumers" and was a way of geeing them up. That's all very well but it just provides ammunition for people to argue that the figures are all cooked-up and can safely be ignored.

We need much better ways to look at the trade-offs in energy consumption because the way that the data is presented today clearly isn't working.