OT Ping TNP UK daily energy use in Hiroshima-bomb equivalents. Reality check.

[Chris Hogg]

I was talking to a slightly green but otherwise intelligent friend about the problems of replacing conventional power generation by renewables. I wanted to bring home to him the scale of the situation, and I remembered your post of a while ago where you said the daily UK energy consumption was equivalent to several Hiroshima-sized atomic bombs. Unfortunately I couldn't immediately find your post to provide the actual numbers, so I did my own calculation, as follows:

Assume the average daily power generation in the UK is 40GW (a bit more in winter, a bit less in summer, but 40 is OK as a rough average).

A gigawatt-day of energy is 8.64 x 10^13 joules.

Hence 40GW-d of energy is 3.456 x 10^15 joules.

The energy equivalent of the blast from the Hiroshima atomic bomb was

15kT of TNT, or 63Tj (63 x 10^12 joules).

Hence the number of Hiroshima-bomb equivalents of energy used by the UK, daily, is (3.456 x 10^15)/(63 x 10^12), = ~55

and which is equivalent to ~0.82 megatons of TNT

After more searching I eventually found your post, with the following: "the UK needs JUST FOR THE GRID half a megaton of energy, in nuclear bomb terms, every day. That's around 20 Hiroshima sized bombs" from a post in the thread "Renewable energy 'simply WON'T WORK': Top Google engineers" around November last year.

As you can see, those numbers differ from mine, by around a factor of two. The question is, who's correct? I can't see an obvious fault with mine, but maths never was my strong point, especially when it comes to giga's and tera's and other higher powers of ten so I may well have got something wrong, but what?

Your comments welcomed!

[The Natural Philosopher]

First off I think I would say the average grid is 35GW

mysql> select avg(demand) from day;

+------------------+ | avg(demand) | +------------------+ | 35338.7484480826 | +------------------+

That takes you down to around .7 megatons

I was probably doing very rough and quick back of envelope stuff when I posted that so an order of magnitude was where I was aiming to be.

I also think I took 25 kilotonnes as the Hiroshima equivalent, whereas you take 15, and the wiki suggests it actually was 13..

Not sure where I dredged that figure for the yield up from.

The intention was not to be accurate to three decimal places, but to get across some idea of the vast amount of energy that a modern post industrial society (has to) consume in order to survive at all.

And some idea of the danger of storing - say - a day's sunlight for use at night, if that storage could 'let go' in an instant.

[Chris Hogg]

OK, and thanks. I'll modify my numbers accordingly, particularly the average demand. The blast yield at Hiroshima was never very accurately arrived at, always a bit of a guesstimate.

[Tim Streater]

For the sort of rough calculation being done, it really doesn't matter a damn. As TNP says, we're not after a figure that is correct to three or four significant figures. You're getting a number that gives you a feel for the amount of energy involved. That's the point.

You might ask your friend to imagine, or calculate for him, how much energy is flowing down that row of electricity pylons you can see in the distance. Or take the number of kWh that the UK uses in a day, and convert to litres of oil (a litre of heating oil contains about 10kWh) to give an idea of the amount of energy we use. And if he asks why we use so much, point a finger at him and say "because you and 59,999,999 others like you want us to".

[Chris Hogg]

Well, of course, but I was a little concerned when my numbers were out by a factor of 2, in case I'd got it badly wrong.

[Brian-Gaff]

I think one of the things that stuck in my mind when the idea of fusion power was discussed on a radio show was this, and I'd love to know how accurate it is. The learned guy said: The energy locked up in the wood in a matchstick is enough to lift mount Everest 1 foot off the ground. Seems rather unlikely to me, and since the amount of energy needed to break all those bonds is not inconsiderable it is pretty pointless as a fact. Brian

[Chris Hogg]

Remember E=MC^2. The energy released by the Hiroshima atomic bomb amounted to the equivalent of only 0.6g of mass. I guess a matchstick weighs a bit more than that. But as you say, accessing that energy is difficult. Perhaps it was in a Trivial Pursuit question.

[tabbypurr]

So it would lift mount everest a foot, yet only move your car a few inches if that. On level ground. OK.

NT

[Vir Campestris]

If you were able to convert all the mass in the matchstick into energy then it would lift Mt Everest a foot.

If you burn it it might move your car a few inches. But in that case almost all of the mass is still around in the form of CO2 and H2O.

Andy

[Tim Streater]

Quite correct. Not that this has anything to do with fusion, mind.

[Tim Watts]

It's easy - you just need to strike the match on an antimatter matchbox!

[Tim Streater]

Then the anti-matchbox and its anti-matches would annihilate with your hand that was holding it, releasing rather more than a Hiroshima's worth, I should think.

[whisky-dave]

how much does a match wiegh about ~0.8g, E=MC^2

I heard from an astromoner (IIRC) that the energy the sun burns in 1 second is enough energy to raise the himalayas 64KM ! Not sure how to work threse things out though.

[harry]

He's referring to the nuclear energy, not the chemical energy.

All this is Daily Mailish. Water measured in "Olympic swimming pools". Area in "football pitches" And length in "London buses"

And now energy needs in "Atomic bombs"

OK for the simple minded I suppose..

[Chris Hogg]

For once you are right Harry! Which is why I wanted to express it in those terms for my 'green' friend.