Four candles!

2009-03-31

A hilarious blunder in my previous article about candles has me out by a factor of 10 on the calorific value of candles. In that article I said wax has about the same calorific value as butter, 3 kJ/g. It turns out that the calorific value of butter is about 30 kJ/g. Oopsie.

That means one modest candle burns at 75 W (not 7.5) and four candles burns at a whopping 300 W! So if you lit any candles then you were probably emitting more carbon than the “business as usual” scenario of having a couple of lights on.

This more or less confirms my prejudices that Earth Hour was a pointless and futile gesture so you could be seen to do something, without actually having to bother to go carbon free.

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10 Responses to “Four candles!”

  1. Pute Says:

    There are two issues involved here. One is energy consumption, the other is greenhouse gas release. The relationship between the two is complex.

    How much carbon dioxide is released by burning a candle for an hour?

  2. drj11 Says:

    Sure. To a first approximation we can treat wax as being the same as oil, they’re both longish simple hydrocarbons.

    Some street-fighting chemistry suggests that burning N*(CH2) gives N*(CO2). Clearly we can neglect the mass contribution from the H and assume that wax is mostly carbon. And obviously O and C are about the same mass, so burning 1 kg of wax, gives about 3kg of CO2. (in fact the assumption that O is about the same mass as C “cancels” the assumption that wax is mostly C; the 3 to 1 ratio is quite close to reality).

    So our 9g per hour candle produces 27g per hour CO2.

    In either case the candle or the power station can produce light sustainably. So these numbers are only useful if you are assuming equivalently fossil fuel sources.

  3. Rainier Wolfcastle Says:

    If you go to the Earth Hour website’s About page, you’ll find that the whole idea of Earth Hour is to show political leaders and decision makers that millions of people care about climate change. There is nothing there about how much carbon would be saved by the observance of Earth Hour itself.

  4. Nick Barnes Says:

    The risk is, of course, that people will come away from Earth Hour thinking that they’ve done their bit.

  5. mathew Says:

    I used LED candles powered by 1.5V batteries.

  6. drj11 Says:

    @mathew: Almost certainly the most efficient way to provide small amounts of low-level light. And LEDs seem destined to be soon the most efficient way of providing more or less any sort of light.

  7. Nick Barnes Says:

    Batteries are surely not a particularly efficient way of doing anything. At least, anything which can be done without batteries.

  8. drj11 Says:

    Oops. Surely you are right.

  9. Jym Says:

    =v= I wonder whether setting SUVs on fire emits more carbon than leaving them operational.


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