How Many Electric Car Owners Does It Take To Change a 60W Lightbulb?

Thursday 1st September, 2011
It's almost impossible to miss the news that "old fashioned" incandescent 60 Watt light bulbs will soon be outlawed by the EU, forcing buyers to replace them with more energy efficient CFL units.

I'm all for saving energy, even though these replacement units do give off a rather odd light and most are useless with dimmer switches, but is it not a case of double standards if we aren't allowed to use 60 Watt light bulbs whilst an electric car owner up the road can happily plug in the 2400 Watt charger for his car?

I thought I'd do a bit of maths. How many 60 Watts light bulbs will we need to replace to save enough electricity for just one Nissan LEAF fully electric car?

For the purposes of the test, we'll assume that each 60 watt bulb is used for an average 3 hours each day. In Summer, electric lighting is hardly used at all. In winter, it will be used a little bit longer. In some rooms, like living rooms, usage may be high but in others such as dining rooms, bedrooms etc. there will be considerably less usage. We'll also assume the LEAF owner will drive 10,000 miles per annum and achieve an average 80 miles from each of their 24 kWh full charges.

At this point, make a guess for how many bulbs you think it might be, then see how close you were below.

Each 24kWh charge uses 24,000 Wh (Watt hours) of electricity. This moves the car an average 80 miles.
24,000 divide by 80 miles gives up a nice round figures of 300 Wh per mile.

Now we can work out that 10,000 miles  times 300 Wh per miles gives us 3,000,000 Wh per year. Yes, 3 million Wh per year, or 3 MWh (MegaWatt hours)

Our 60 Watt bulb is used for 3 hours a day but our replacement CFL bulb will still use 11W each hour too, so we're only saving 49Wh per hour, a total saving of 147Wh per day.

There are 365 days in a normal year, so our light bulb replacement will save us 147 x 365 = 53,655 Wh saved each year.

So now we just need to work out how many bulbs, at 53,655 Wh saving each we need to replace to save 3,000,000 Wh of electricity.

3,000,000/53,655=56 bulbs

So, based on living room, hallway, kitchen, downstairs toilet, 3 bedrooms and a bathroom, that's 8 bulbs per house.

So, if seven households replace every 60W lightbulb in their home, we may save enough electricity to power just one electric car for an average 10,000 miles.

With most households now having two cars that cover more than 10,000 miles between them, I think we'll need to do a little more than replace a few bulbs to reduce energy consumption in the future.

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