04 August 2011

Sustainable Energy: Without The Hot Air

You can get a digital copy of this book for free. Or get a paper copy on amazon.com.

Reading this book should be a prerequisite for having a conversation about energy policy. Like balancing the budget, the question of how we make the transition from fossil fuels to sustainable power sources requires a quantitative approach with quantitative questions. And, like in the discourse around balancing the budget, people regularly make insane, impossible, or useless proposals because they don't know any better (or they think they can get away with it).

Sustainable Energy, by David JC MacKay, tries to establish a solid numerical foundation for such discussion. At its heart is the question: Is it possible to switch all our energy production from fossil fuels to sustainable sources? And this is more or less an arithmetic question. Either the supply of energy available (given technological projections) can meet demand, or it can't.

MacKay lays out the numbers for various classes of energy consumption and energy production. It turns out that you can reach some nontrivial conclusions just based on very crude lower and upper bounds. For example, what are major uses of energy? MacKay estimates that the typical Briton, who makes a transatlantic plane flight once a year, has a carbon footprint on that single flight of approximately the same as his carbon footprint due to driving during the remainder of the year. And we are not going to make planes that are substantially (say, more than 2x) more efficient than they are today; physics provides a pretty clear lower bound there on the amount of energy that is needed to fly people around. In total, transport (planes plus ground transport) accounts for about a third of total energy usage in developed countries. So to make a dent in total energy usage, we are likely to have to either dramatically cut the amount we fly, or make ground transport much more efficient. (MacKay advocates the electrification of cars as one of the most significant things we can do.)

Conversely, it's also important to know what classes of energy usage account for only small portions of total usage. Lighting in homes and businesses? Around 5% of total usage. Vampire wall warts (like cell phone chargers)? Around one quarter of one percent. Now, some people will insist that "every little bit helps". While this is true in a superficial sense, we can't delude ourselves into thinking that we can, say, halve our energy consumption by implementing ten (or 200) "tiny" interventions like replacing incandescent bulbs or unplugging cell phone chargers when they're not in use. They won't add up. It just can't be done unless you touch the heavy hitters: transport and heating (together, about two-thirds of energy usage). You have something like the equivalent of Amdahl's law here, which upper bounds the total savings even if you were to optimize one class of usage completely away. To think that you can somehow dance around this mathematical constraint is madness.

MacKay reaches a sobering conclusion: for developed countries, making the switch away from coal will require industrialization of vast amounts of land. Whether it's designated for tide power, solar farms, wind farms, biofuel farms, geothermal installations, or something else, we're going to need a hell of a lot of it. (If you find this unpalatable, have we mentioned nuclear power?)

We have been implored at one time or another to try and reduce carbon emissions by carpooling, installing LED lights, eating less meat, not using plastic bags, turning down the volume on the television, breathing more slowly, etc. But we have to pick our battles, and that requires a cost/benefit analysis. I always get annoyed when I hear on the radio a useless and impossible-to-evaluate comparison of the form, "If we all just [made some change], it would be like {taking [large number of] cars off the road, planting [large number of] trees, heating [large number of] homes for free, etc}." Sustainable Energy convinced me that there is a response superior to smashing the radio with my hands, namely, doing some back-of-the-envelope math.

This is a very important book. Did I mention it's free to download? Highly recommended.

1 comment:

  1. He was my TA for a neural networks class, some 20 years ago. Very smart guy.