May 19, 2006
MIT Team Sees Thermophotovoltaics As Car Power Source

Here's an unusual approach for generating electricty in a car: Imagine burning fuel to generate an extremely bright light so that the light can strike photodiodes to generate electricity for the various subsystems in cars that need electricity.

MIT researchers are trying to unleash the promise of an old idea by converting light into electricity more efficiently than ever before.

The research is applying new materials, new technologies and new ideas to radically improve an old concept -- thermophotovoltaic (TPV) conversion of light into electricity. Rather than using the engine to turn a generator or alternator in a car, for example, the new TPV system would burn a little fuel to create super-bright light. Efficient photo diodes (which are similar to solar cells) would then harvest the energy and send the electricity off to run the various lighting, electrical and electronic systems in the car.

Such a light-based system would not replace the car's engine. Instead it would supply enough electricity to run subsystems, consuming far less fuel than is needed to keep a heavy, multi-cylinder engine running, even at low speed. Also, the TPV system would have no moving parts; no cams, no bearings, no spinning shafts, so no energy would be spent just to keep an engine turning over, even at idle.

"What's new here is the opportunity for a much more effective energy system to be created using new semiconductor materials and the science of photonics," said Professor John Kassakian, director of the Laboratory for Electromagnetic and Electronic Systems (LEES), where the work was conducted. The idea is to create intense light, let it shine on new types of photo diodes to make electricity, and bounce any excess light back to the light source to help keep it glowing-hot. In theory, Kassakian said, efficiency could be as high as 40 percent or 50 percent.

Of course the "In theory" part means they haven't yet achieved such a high level of efficiency. But I'm surprised that burning fuels could be made to emit such a high percentage of their energy as photons to even make possible such a high efficiency for electric generation. If such a high level of efficiency could be achieved then it would have a lot of other practical uses. How about burning fuel to generate electricity for houses or commercial buildings? Or why not use the electricity to power the car rather than use an internal combustion engine?

Share |      Randall Parker, 2006 May 19 04:32 PM  Energy Transportation


Comments
carl said at May 20, 2006 8:35 AM:

Or, why not convert the fuel into heat and use improved thermoelectric chips (e.g., http://www.powerchips.gi/).

Bob Badour said at May 20, 2006 10:45 AM:
Or why not use the electricity to power the car rather than use an internal combustion engine?

Because one loses 50% to 60% of the energy in the conversion. The electric motor would then have comparable losses on the remaining 40% to 50% remaining.

carl said at May 20, 2006 11:19 AM:

Bob, as long as we are talking about hypothetical fuel -> light -> electricity conversion, I think we can talk about hypothetical fuel -> heat -> electricity conversion beyond current standards much like the (non-existing) powerchip. With current technology, neither method works.

Nick said at May 20, 2006 7:18 PM:

Waaait a minute. They say they hope to get 50% efficiency on the whole system?

Incandescent light bulbs (a better analog to combustion than flourescent, mercury/sodium vapor, LED's etc) only convert light at about 5% efficiency. The best existing (expensive 3 layer, used for satellites) PV is 38%, and the best theoretical PV efficiency I've seen (with experimental nano-tech) is 60%. If they're going to get 50%, then they'll need to get, say, 70% combustion to light, and 70% light to electricity.

Any idea how they plan to get such high light-to-electricity efficiency? That alone would change everything....

Randall Parker said at May 20, 2006 9:54 PM:

Nick,

I do not get it either. Is there some way to burn fuel and get the vast bulk of it as light? Isn't most fuel burn converted into heat energy? I have no idea.

PacRim Jim said at May 21, 2006 12:15 AM:

Put piezoelectric chips in the tires and generate electricity by rolling. Second Law of Thermodynamics be damned.

Paul Dietz said at May 21, 2006 4:09 AM:

Incandescent light bulbs convert energy to electromagnetic radiation at considerably higher efficiency than 7%. It's just that much of that radiation isn't visible light, it's near IR. Thermophotovoltaics would have PV cells tuned to convert near IR to electricity, and by controlling the emission from the source (or by recycling off-peak photons) the effective spectrum at the PV cell can be made very non-thermal, which allows one to boost efficiency. I do find the 50% figure to be a bit optimistic, but who knows.

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