68 The BBC News has been warning us ... unplug your mobile-phone charger. The BBC News article from 2005 said: "the nuclear power stations will all be switched off in a few years. How can we keep Britain's lights on? Here's three ways you can save energy: switch off video recorders when they're not in use; don't leave televisions on standby; and unplug your mobile-phone charger when it's not in use."
Gadgets: 5 Light: 4 kWh/d
Heating, cooling: 37 kWh/d
Jet flights: 30 kWh/d
Figure 11.5. Information systems and other gadgets.
Deep offshore wind: 32 kWh/d
Shallow offshore wind: 16 kWh/d
Biomass: food, biofuel, wood, waste incin'n, landfill gas: 24 kWh/d
Solar heating: 13 kWh/d
Wind: 20 kWh/d
68 Modern phone chargers, when left plugged in with no phone attached, use about half a watt. The Maplin power meter in figure 11.2 is not accurate enough to measure this sort of power. I am grateful to Sven Weier and Richard McMahon of Cambridge University Engineering Department who measured a standard Nokia charger in an accurate calorimeter; they found that, when not connected to the mobile, it wastes 0.472 W. They made additional interesting measurements: the charger, when connected to a fully-charged mobile phone, wastes 0.845 W; and when the charger is doing what it's meant to do, charging a partly-charged Nokia mobile, it wastes 4.146 W as heat. Pedants sometimes ask "what about the reactive power of the charger?" This is a technical niggle, not really worth our time. For the record, I measured the reactive power (with a crummy meter) and found it to be about 2 VA per charger. Given that the power loss in the national grid is 8% of the delivered power, I reckon that the power loss associated with the reactive power is at most 0.16 W. When actually making a phone-call, the mobile uses 1 W.
Further reading: Kuehr (2003).
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