Numbers are good

One strong prejudice which has been reinforced by wading through a tiny fraction of the material around on decarbonising energy is that numbers are good. Not ultra-precise ones, just reasonable estimates, with all the right reasons included.

David J Mackay at Cambridge shares that view, as a rather excitable post at The Register describes at length. In fact he’s compiled, I think that’s the right word, a whole book of hand-waving physics to assess whether renewables can supply the UK’s energy needs. (answer no, or not without a significant contribution from nuclear power – he is not advocating this, or at least not admitting to it, just showing how the numbers stack up. You can download the whole thing – with a few bits still unfinished, here.)

There is a nice old-fashioned scientists’ conviction here that the facts speak for themselves, though he talks a bit about ethics too. But it is at least better to have these kind of facts than not.

A good example is his analysis of the carbon capture scheme being developed with encouragement from Wally Broecker, as mentioned a few posts ago and described in Broecker and Kunzig’s Fixing Climate. It has been reported as a possible route to the get out of jail free card we’d all secretly – or overtly! – like to relieve the pressure of thinking about climate change realistically.

Sorry, says Mackay in his blog, the physics puts a dampener on this, as physics will:

“there is a problem with the way this carbon scrubbing technology is being discussed. The problem is energy: how much energy does Lackner’s CO2-capture method require. `Not very much’? Come on, we need numbers, not adjectives.

Here are some of the numbers required for a coherent conversation about carbon capture. Grabbing CO2 from thin air and concentrating it into liquid CO2 requires energy. The laws of physics say that the energy required must be at least 0.24 kWh per kg of CO2. What does Lackner’s process require? In June 2007 Lackner told me that his lab was achieving 1.3 kWh per kg. Let’s imagine that further improvements could get the energy cost down to 0.7 kWh per kg of CO2.

Now, let’s assume that we wish to neutralize a typical European’s CO2 output of 11 tonnes per year, which is 30 kg per day per person. The energy required, assuming an exchange rate of 0.7 kWh per kg of CO2, is 21 kWh per person per day. For comparison, British electricity consumption is roughly 17 kWh per person per day.

So as a ballpark figure, the Broecker/Lackner plan requires an amount of energy equal to current electricity production.”

Maybe if you made the electricity using waves or wind, you could still clean up after all the cars and trucks – but then you need to follow through Lackner’s detailed aproximations of how much land surface, and how much material, this level of energy generation would actually need…

He did make me keener on the Severn barrage, though.. which would be handy for Bristol. I know there’s a national grid but as we are going to have to watch the estuary get re-engineered perhaps we’ll get first call on the electrons?  More seriously, it fits one of his themes, which is that climate and energy is a really big problem, (quantified) and everyone doing a little bit will only make a little difference. Do the sums.

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