Thursday, June 30, 2011

Fusion Jazz: Why Fusion Power Is Doomed

The National Ignition Facility (NIF) is a US-funded project to produce power from fusion, that is, by smacking together light atoms rather than busting up heavy atoms as in ordinary nuclear reactors. At the NIF, flashes of light from giant lasers zap tiny pellets of hydrogen, triggering fusion.

A recent New York Times article on the $4-billion facility illustrates the difficulty of staying oriented to reality in the face of mind-boggling gadgets as big as office buildings that tap into forces of nature most of us don’t really understand. The article, “Fusion Experiment Faces New Hurdle,” states that

The tipping point for nuclear fusion is “ignition,” the moment when the lasers release the same amount of energy that is required to power them.

Who doesn’t love ignition? “We have ignition!” is what the Apollo mission controllers used to say just as the flames burst out of the giant rocket and it flew up to glory. I often repeat the same phrase, probably annoyingly, when I light a fire in our woodstove. Ignition is when things light up and really get going. But it’s elusive for fusion, as the NIF’s backers admit: people have been trying to figure fusion out for half a century, lured on (and luring others on) with the promise of clean, inexhaustible electricity . . . someday. Ah, if only we could achieve ignition. The facility’s backers claim that they will do so within a year.

Bringing hype to Earth, too.

But there’s something fishy about the goal itself. First, in almost any other setting, “ignition” denotes the beginning of a self-sustaining reaction, energy from burning fuel causing further burning of fuel. But the fusion reactions that the NIF proposes to “ignite” are not even close to self-sustaining in this sense: they will flicker into being and then go dark a fraction of a second after the giant laser flash ends. In this context, “ignition” is merely the condition in which as much energy, in the form of raw heat, is released by the fusion reaction as is required, in the form of laser light, to make it go. (In the NIF’s words, “ignition is defined as fusion energy output greater than or equal to laser energy incident on the target.”) Let’s assume, generously, 100% efficient lasers that deliver precisely as much energy to the fusion reaction as they consume in the form of electricity. What the NIF proposes to achieve, therefore, is not what most of us would call “ignition” at all but, at best, energy breakeven: heat out equals electricity in.

But treating electricity and heat as comparable forms of “energy” is as dubious as treating pizza and sewage as comparable forms of “matter.” An ordinary coal-fired or nuclear power plant, which releases heat from fuel to boil water to run turbines to spin generators to churn out electricity to run our cell phones and light bulbs, is forced by basic physics to throw away about 60% of the heat it obtains from fuel. You can turn electricity entirely into heat, but you can’t turn heat entirely into electricity. This is because heat is perfectly disorganized energy, energy flying every which way, while electricity is highly organized and can be used to do almost anything. Likewise, you can turn 100% of a pizza into sewage (by eating it) but you can only turn a fraction of your sewage into pizza (by using it as fertilizer and growing wheat, tomatoes, and dairy cows from scratch). Electricity is energy pizza, and heat is energy sewage. The NIF is proposing to turn X units of pizza into X units of sewage, and this it calls “ignition.”

The NIF’s Holy Grail is therefore, to be blunt, meaningless (though the Times quotes it as if it made sense). If fusion is contending to be a viable power source, a less absurd goal would be to produce at least as much useful energy — not mere heat, but electricity as is consumed. Because of inevitable heat-to-electricity losses, this means that a fusion facility would have to produce about 2.5 times as much energy in the form of heat as it consumes in the form of electricity, counting not just its lasers (as the NIF does) but its power electronics, air conditioners, pumps, computers, bathroom lights, and every other scrap of overhead. And that goal will be much, much harder to achieve than mere input-output parity.

But even electric-in, electric-out breakeven would be, in itself, useless. A lump of cold rock has achieved “ignition” by that standard; a fusion facility that merely balanced electricity in with electricity out would be nothing but a cyclopean, multi-gigabuck paperweight. To be useful, it would have to produce a large electric surplus and do so at low enough per-kilowatt-hour cost to be competitive with all other available sources of equally clean (or cleaner), inexhaustible electricity, such as wind or solar power (with, let's say conservatively, enough storage capacity thrown in to make them dispatchable around the clock). And these competitors are getting cheaper all the time, according to standard learning curves.

The NIF’s apples-to-kumquats breakeven standard is, I believe, touted by fusion advocates because it is the only standard that fusion has a prayer of satisfying in this century — or any other. A fusion reactor that churns out net useful electric power at a per-kWh price competitive with realistic, equally clean (or cleaner) alternatives is almost unimaginable, even in the remote future — when those renewable alternatives will be even cheaper than today due to technological improvements.

It would be hard to set up a more hopeless contest. Fusion is a solid-gold tortoise starting a thousand miles behind a whole pack of very healthy, focused jackrabbits, all of whom already have a claw over the finish line.

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