Sustainable Energy â without the hot air?

David J.C. MacKay has a draft book out online, , which is worth a browse. He is due to give a talk here in a bit, which should prove interesting.

The book is an attempt to look at renewable energy from a broad-brush numbers point of view (in which I suspect it does a rather better jobs than "Heat" by Monbiot). But the bit I want to look at is the "offsetting" section, p143 onwards, the Story of Joan and Thambo. Joan flies in a plane, and offsets her emissions by helping Thambo keep warm by not burning his pile of coal. This seems fair enough: she emits X CO2 but her offset money allows Thambo to not emit X. The example assumes that all is above board, as it might not be in the real world. Yet for some reason MacKay seems to view this with suspicion, because the Joan+Thambo combination is not emitting *less* CO2. But this is silly... the purpose of the offset it only to remove what you emit (though you could buy 2* offsets; or just buy the offsets without travel).

What he doesn't really address is what happens when we run out of such easy methods to offset CO2, which I suspect is a much bigger problem.

Incidentally, p148 has a nice graph of what happens versus the costs of a carbon tax. According to his estimates, sequestration of CO2 from thin air occurs at $130 (per tonne) and impact on US car-driving only occurs at $400. Carbon offsetting, though is available from $7.50.


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Without reading the whole thing I can't see where he gets his extracting from thin air numbers. Any pointers?

[p152: Cost of sequestration from the air From another chapter: unavoidable laws of physics guarantee that the energy cost of creating one kg of liquid CO2 from thin air (that is, not at a power station or similar source where CO2 is more concentrated) is 0.24 units. Assume a factor of 3 for inefficiency, then we have 0.72 units per kg. So 720 units per tonne of CO2, which costs about £20 at retail price of 3p per unit ($37); or £72 at 10p per unit ($130). This is a theoretical possibility only: I don't know whether any technologies could sequester CO2 at this price; and these prices don't include the cost of transporting and storing the CO2 once it is captured. So its theoretical only -W]

Having come across this research done at ECN, I also had to think of that fact.

"A cost evaluation of CO2 sequestration by aqueous mineral carbonation has been made using either wollastonite (CaSiO3) ... Estimated costs are 102 ... â¬/ton CO2 net avoided for wollastonite ..., the major costs are associated with the feedstock and the electricity consumption for grinding and compression (54 and 26 â¬/ton CO2 avoided, respectively)."

Great resource but he screws up in more than a few places. His analysis of windmills on wildlife needs a little work. It's true that cats kill a lot of animals. U of W says feral cats might kill 217 million birds per year in Wisconsin alone. The problem is that these statistics are for sparrows, warblers and other small field birds. The real problem with windmills is when somebody puts a giant farm right in the middle of a migratory route of an endangered eagle. MacKay mentions 9 white-tailed eagles killed in Norway. When you compare these two numbers you can't help but laugh at the enviros that protest windmills. But on the other hand if you look at the Altamat pass in California something like 50,000 predatory birds (many of which were protected) were killed by windmills in the last 20 years. 50,000 is a lot more than 9. And of the 217 million bird deaths from cats in Wisconsin I really doubt any of them were eagles. Although apparently not from the lack of trying (great pic). Yes I understand the food link but still... there are hawks outside of my house that love to eat cats.

There are solutions that can be explored of course. Some of which include adding rocks and tall grass to protect rodents around the windmills. I haven't seen any wind farms employing this tactic though.

So it would appear he accidentally misrepresented the windmill situation about as much as Al Gore misrepresents the urgency of unplugging your cellphone charger. I could very well be wrong but that is my current level of understanding.

That book is a wealth of information. I'd love to know how long it took him to write it.

Hm, in the book we can read also this:

"So, if you want to be fair, you now know that that round-trip flight in the 747 uses up more than your whole annual allowance!" - so how can I go to a scientific conference across the Europe, for instance?

Simply, the prices of aviation should go up... and the money should then be used for increasing the energy use efficiency.

Simply, the prices of aviation should go up... and the money should then be used for increasing the energy use efficiency.

Agreed. You shouldn't be allowed on a plane within Europe for less than £200 each way.

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