Admittedly, some older chargers use more than half a watt – if it’s
warm to the touch, it’s probably using one watt or even three (figure 11.3).
A three-watt-guzzling charger uses 0.07 kWh per day. I think that it’s a
good idea to switch off such a charger – it will save you three pounds per
year. But don’t kid yourself that you’ve “done your bit” by so doing. 3W
is only a tiny fraction of total energy consumption.
OK, that’s enough bailing the Titanic with a teaspoon. Let’s find out
where the electricity is really being used.
Table 11.4 shows the power consumptions, in watts, of a houseful of gad-
gets. The first column shows the power consumption when the device is
actually being used – for example, when a sound system is actually play-
ing sound. The second column shows the consumption when the device is
switched on, but sitting doing nothing. I was particularly shocked to find
that a laser-printer sitting idle consumes 17 W – the same as the average
consumption of a fridge-freezer! The third column shows the consump-
tion when the gadget is explicitly asked to go to sleep or standby. The
fourth shows the consumption when it is completely switched off – but
still left plugged in to the mains. I’m showing all these powers in watts –
to convert back to our standard units, remember that 40 W is 1 kWh/d.
A nice rule of thumb, by the way, is that each watt costs about one pound
per year (assuming electricity costs 10p per kWh).
The biggest guzzlers are the computer, its screen, and the television,
whose consumption is in the hundreds of watts, when on. Entertainment
systems such as stereos and DVD players swarm in the computer’s wake,
many of them consuming 10 W or so. A DVD player may cost just £20
in the shop, but if you leave it switched on all the time, it’s costing you
another £10 per year. Some stereos and computer peripherals consume
several watts even when switched off, thanks to their mains-transformers.
To be sure that a gadget is truly off, you need to switch it off at the wall.
According to Jonathan Koomey (2007), the computer-servers in US data-
centres and their associated plumbing (air conditioners, backup power sys-
tems, and so forth) consumed 0.4 kWh per day per person – just over 1%
of US electricity consumption. That’s the consumption figure for 2005,
which, by the way, is twice as big as the consumption in 2000, because the
number of servers grew from 5.6 million to 10 million.