Goose the Blog 2.0

"Oh, ha! Sarcasm: The last refuge of sons of bitches!"

not promising news

by John at 7/18/2007 12:59:00 PM

I few days ago, I read an article (pdf, 9.5 Mb) transcribed from a speech by Nate Lewis, a Caltech chemistry professor, in Caltech's quarterly periodical, Engineering and Science. Lewis used to teach freshman chemistry and was always pretty popular because, I guess, he was a funny guy. I never took his class.

Anyway, Lewis gave a talk about the future of energy use in the world, especially concerning ways to stabilize the level of CO2 in the atmosphere. After analysis for population growth, GDP growth, efficiency improvements (which includes conservation, I think), and the carbon-to-energy ratios of fuels used, he calculates that to stabilize atmospheric CO2 to 550 ppmv* (parts per million by volume - for the last 670,000 years, CO2 has been 200-300 ppmv - it is now 380 ppmv) we would have to have online, by 2050, enough carbon-free energy generation capacity to equal the total energy generation capacity we have today. That is, we would need about 10 terawatts of carbon-free power, if we start now. If we don't start for 30 years, we'll need 15-20 terawatts of carbon-free power by 2050.

Here is where it gets "not promising."
  • To get that much carbon-free energy, we would have to build a new 1 gigawatt nuclear reactor every other day for the next 40 years. Because nuclear plants have a 50 year lifespan, we will have to go on building them forever. Also notable: There is not enough uranium fuel to power all those reactors, so we will have to use plutonium, which exacerbates the threat of nuclear weapon proliferation.
  • We don't have time to wait until nuclear fusion is demonstrated (there has been a 35 year horizon for this technology for the last 50 years).
  • Carbon sequestration pumps the CO2 underground where we hope it stays, but, while we may have the capacity to store all the CO2 generated, the technology is not proven, and if it works, if uniformly distributed, the CO2 generated by the United States and pumped underground would raise the elevation of lower 48 states by 5 centimeters.
  • There are about 0.9 terawatts of economically accessible hydroelectric power, but we are already using 0.6 terawatts of it.
  • Geothermal power has about 11 terawatts of power spread out over all the landmass of the globe, but capturing it is far less than 100% efficient.
  • Windpower can generate about 2 to 4 terawatts over the entire surface of the Earth.
  • Biomass could make available 20 terawatts of power (if growing and harvesting do not require energy) at a cost of 31% of the total land area of the planet. This isn't in the article, but, for example, using corn to produce ethanol to burn as fuel may actually be energy negative - that is, it takes more energy to make ethanol through fertilizing, harvesting, and manufacturing than you get out of it when it is burned.
  • Solar energy is just about ubiquitous, and plentiful. It would take only six 400km x 400km arrays of modern photovoltaic cells to generate all the power we consume today. That doesn't sound too bad, but my back-of-the-envelope calculation says that one of those 400km x 400km plots is equivalent to about 500 million home roofs. Plus, solar is now 5 to 10 times more expensive than fossil fuels, and you have to be able to store the power generated to use it when it is dark out - one option here is electrolysis of water to form H2, which can be oxidized to form water and generate electricity in fuel cells.
So the viable options are: 1) 10,000 new nuclear power plants, 2) keep on burning fossil fuels but sequester the carbon dioxide, or 3) find a way to make cheap solar power, solve the hydrogen storage and transportation problem, and make fuel cells that work.

And we have to start tomorrow.


* From the article: "Although major uncertainties remain, most climate-change researchers set 550 ppmv as the upper limit of what would lead to about a two degree Centigrade mean global temperature rise. This is projected to have significant, but possibly not catastrophic, impacts on the earth’s climate. For example, the coral reefs would probably all die. But we, as humans, would probably be able to adapt, at some level, to such a change. On the other hand, most people in the modeling effort feel that 750 ppmv or higher would be quite serious."


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