The Second Law and Energy

author: Steven Chu, U.S. Department of Energy
published: March 5, 2011,   recorded: October 2007,   views: 7219

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This Nobel Prize-winning scientist admits to staying up late the night before his talk to bone up on thermodynamics. He puts his research to good use, discussing the history and application of the laws of thermodynamics, which have served as “the scientific foundation of how we harness energy, and the basis of the industrial revolution, the wealth of nations.”

Taking Watt’s 1765 steam engine, Stephen Chu illustrates basic principles of thermodynamics -- that energy is conserved, that you can do work from heat, especially when you maximize the difference in temperature in the system and minimize heat dissipation from friction. Chu offers another form of the laws: You can’t win; you can’t break even; and you can’t leave the game.

The game hasn’t changed all that much in the past few centuries. Nations now burn coal for electricity, achieving around 40% thermal efficiency. Natural gas can be harnessed at higher efficiencies still, and if we could deploy temperature-resistant metals for boilers, even less energy would go to waste. This is a pressing matter, points out Chu, because the planet can no longer afford wanton use of carbon-based fuels. With too much CO2, our global “heat engine” has begun to tip toward a point of no return. So the big question for Chu is whether science can design “entropy engines that can generate sustainable (carbon-free) energy sources.

He describes efforts to capture sunlight with improved solar cells, but notes that a silicon shortage, expensive chips, and a learning curve dictated by Moore’s law mean the technology won’t be widely deployed for 10-15 years -- not fast enough in the battle against climate change. Chu likes the efficiencies of power generation from wind, but there’s a limit to turbine size, and the U.S. high voltage transmission network needs a complete and expensive makeover to take full advantage of wind. Forget corn as biofuel, he counsels, since it “barely breaks even in terms of CO2 saved,” and focus instead on perennial grasses like miscanthus. Chu’s lab and others are looking for microbes that can help turn these plants more readily into fuels.

Another potentially rich energy source, Chu says, involves converting sun light into fuel the way plants do in photosynthesis. But “how does nature split water?” asks Chu. Science hasn’t entirely figured out the molecular machinery that turns water into oxygen and hydrogen. Deriving bioenergy through artificial photosynthesis may mean considering entropy and other basic laws in a different light, Chu suggests. “Nature turns out to be very good.”

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