The Oil Drum | DrumBeat: October 3, 2007

288 comments on DrumBeat: October 3, 2007

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tate423 on October 3, 2007 - 9:18am

http://www.nextenergynews.com/news1/next-energy-news-betavoltaic-10.1.html

Although betavoltaic batteries sound Nuclear they’re not, they’re neither use fission/fusion or chemical processes to produce energy and so (do not produce any radioactive or hazardous waste). Betavoltaics generate power when an electron strikes a particular interface between two layers of material. The Process uses beta electron emissions that occur when a neutron decays into a proton which causes a forward bias in the semiconductor. This makes the betavoltaic cell a forward bias diode of sorts, similar in some respects to a photovoltaic (solar) cell. Electrons scatter out of their normal orbits in the semiconductor and into the circuit creating a usable electric current.

Batteries like this could marginalize peak oil. Does anyone with any sense of knowledge of these think it's scalable? Better yet, does this really work? It reminds me of burning salt water....

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neuroil on October 3, 2007 - 9:27am

It has been discussed in the comments about Robert Rapier's excellent contribution yesterday here .

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Black_Dog on October 3, 2007 - 9:33am

Great! Sounds like a fantastic idea. If it works on the large scale, one could imagine a car that never needs to be re-fueled or re-charged. Just buy it and drive it. However, they don't say what material is to be used as the source of beta emissions. It's likely that the source is the result of radioactive decay. And, the batteries are said to exhibit a lifetime of 30 years, which makes one wonder whether the "death" is a slow, exponential decay or a sharp "that's all folks"...

E. Swanson

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SacredCowTipper on October 3, 2007 - 11:01am

Without reading ... nuclear materials have a half life and beta decay is a nuclear process. The battery will decline in a known curve.

Beta emitted electrons are high energy and there may be some erosion of the zone between the two materials which would reduce efficiency. Your mileage may vary.

And one either has to mine beat emitters or make them using a nuclear reactor ... oh, just followed a link - use tritium for this? Sure ... we're talking long term spaceship batteries that will be less controversial than boosting bits of plutonium into orbit, but that is the only use such a technology will see as far as I can tell ...

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JoulesBurn on October 3, 2007 - 1:07pm

Electrons from beta decay of tritium have an energy of 5.7 keV with a decay constant of 1.8E-9/sec. If one had a kilogram of water with both hydrogens as tritium, this leads to (starting out) a power output of just over 100 watts, which decreases to 50 watts after 12 years. Useful perhaps for the Eveready Energizer Bunny. Since it runs non-stop whether you use it or not, one could trickle-charge a conventional battery and make it power your toaster occasionally. All this assumes, however, 100% conversion of the electron kinetic energy into useful power, which is of course ridiculous. And as others have pointed out, only around 250 kg of tritium (equal to about 1500 kg tritiated water in my example) have been produced in the US since 1955.

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NeverLNG on October 3, 2007 - 10:37am

You can, of course, burn salt water if you put enough energy in to dissociate the water and burn the hydrogen. Of course, what you get back is less energy than you put in.

Same with any battery -- lead acid, carbon-zinc or "betavoltaic." Something separates charges, which are then allowed to slowly recombine in some way that produces a usable current of electrons. It takes far more power to separate the charges than you get back in recombining them -- but doing so can make sense under some conditions: specifically, those things for which we need a portable energy source.

Nevertheless, I have friends who believe that batteries "make" energy, and they can't understand all the fuss about peak oil, because they can just go to the store and buy batteries if the power goes off.

Neutron decay causing "forward bias in the semi-conductor"?? This sounds like bait for ignorant venture capitalists.

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pondlife on October 3, 2007 - 11:37am

Isotope power sources have been around since the cold war. There was some pretty nasty cobalt ones found dismantled/smashed in E Europe by civilians in the 1990s. [sorry no reference]. Those sort used thermocouples and heat, but I am sure there have always been other ways of exploiting radiation. Saying they are not radioactive is wrong.

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thomas deplume on October 3, 2007 - 3:47pm

Betavoltaic devives have high energy density but very poor power density. Generating the 10s of kilowatts a car would need would requires acres of surface area squeezed into a few cubic feet. Nanotech may be able to pull it off. It could be a significant source of energy but time to ramp up to quantities to make that impact would take 10 to 20 years which we may not have. A prime candidate for fuel would be potassium 40 which is the most abundant radioactive isotope in the world. It has a half life of about 29 years.

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Kevembuangga on October 3, 2007 - 4:07pm

A prime candidate for fuel would be potassium 40 which is the most abundant radioactive isotope in the world.

Sure Tom, sure, no problem.
Just need to mine it, separate from the non radioactive, prevent it to burn off the factory while it's not yet packed in the batteries, etc...

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wehappyfew on October 3, 2007 - 5:14pm

Ahhh.. no.

Potassium 40 has a half-life of 1,250,000,000 years, not 29 years. It is, indeed the most abundant radioisotope (or pretty close to it), and is responsible for a sizable amount of the internal heat generated in the Earth.

But its concentration in natural potassium is .0001

Extraction costs would be high (centrifugal separation of isotopes differing by a few percent), and the energy payback time would be a significant fraction of the lifetime of the Universe.

Tritium is no good either. Too expensive, too dangerous in useful amounts.

Carbon14 is better, easier to make, but still astronomically expensive, and far, far more dangerous. Imagine a car powered by Carbon14 decay... any crash that breaches the containment vessel makes the entire neighborhood uninhabitable for 50,000 years or more.

Forget all betavoltaic applications except for space probes and such.

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