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MIT Developing New Thermophotovoltaic System for Vehicle Power

Essential parts of a TPV system. Source: MIT LEES

MIT researchers are working to improve an old concept—the thermophotovoltaic (TPV) conversion of heat into electricity using photovoltaic (PV) diodes—to power vehicle electric subsystems.

The new TPV system would use a small amount of fuel to heat an emitter to approximately 1,500 Kelvin (1,227° C), shine the resulting intense light on new types of photo diode cells to generate electricity, and bounce any excess light back to the light source to help keep it glowing-hot.

Such a light-based system would not replace the car’s engine, but it would consume far less fuel than currently required to keep a heavy, multi-cylinder engine running, even at low speed. In theory, TPV system efficiency could be as high as 40% or 50%.

The system consists of a vertical-cavity enhanced resonant thermal emitter, a spectral control component and PV cells. The PV cells, made of a new material such as gallium-antimonide, would surround the glowing emitter picking up the radiated light.

A highly specialized filter—the spectral control component—set between the two, would let the most useful light wavelengths pass through to hit the photo diodes, while reflecting light of less useful wavelengths back to the heating element, pumping up the temperature.

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.

—Professor John Kassakian, director of the Laboratory for Electromagnetic and Electronic Systems (LEES)

The relatively high efficiency compared to photovoltaic systems in use today is expected to come from the ability to fine-tune all three main parts of this system: the light emitter, the photo diode cells, and a way to scavenge light at wavelengths that might otherwise be wasted.

The concept of TPV systems is not new. In the late 1960s and early 1970s, much research was done on TPV and light-harvesting technology, first to create solar energy systems for spacecraft, and then in response to energy shortages that spurred an intense burst of research into various alternative energy technologies. It is the advances in the various constituent technologies that now makes this more viable.

This new technology is what makes it a very attractive system. There are the new materials that let us build more appropriate photo diodes. There’s our new understanding of photonics that lets us build the selective emitters. And there’s the photonic band-gap filter, made of thin silicon and silicon-dioxide layers that act as selective mirrors, letting the desired wavelengths through and reflecting back the rest.

—John Kassakian

Cooling remains an issue to be solved, and the team is working with different materials to see which work best in terms of light emissions, light harvesting and light reflection.

The researchers are focusing on developing an automotive system that will take excess heat from the TPV system and use it to drive the car’s heating and air conditioning systems. This would replace both the alternator and air conditioner, both of which are now run by the engine.

TPV systems could mesh with hybrid vehicle technology, and be applied to providing auxiliary power for long-haul trucks.

Initial funding for the research was from the MIT/Industry Consortium on Advanced Automotive Electrical/Electronic Components and Systems. The work is presently funded in part by Toyota, but Toyota has made no decision to develop this technology for automobiles.




They need to make a longer-wavelength version which can operate on engine exhaust heat.


Actually, I believe the A/C in the hybrid Camry runs of electric power.

If Toyota is partly funding this, you can bet they have a real interest in this technology, so expect to see it show up in some form on production vehicles.


There is potential for using this for co-generation in a lot of different places - from wood stoves to nuclear reactors.


Fantastic if it scales and is not too expensive.
I assume you could burn the fuel in a very clean way and so get a cleaner electric car running on Gasoline !
(or diesel) or any biofuel.
No hydrogen required !

allen zheng

LochDhu, Engineer-Poet:
You are correct, the US will need an additional 50% increase in electrical power in the next 20 years. Thermoelectrics can provide a very large contribution (80-95% of projected demand increase) without increasing emmisions of GHGs. Further implementation/improvements of thermoelectrics/votaics will improve the efficiencies of heat engines like automobiles, ships, Strerling engines, etc. Add in technologies like plants with co-generation, coal gasification (also eliminates Sulfur oxides and heavy metals), sequestation, algae oil/biomass production, you can start moving away from fossil energy and towards susutainable energy.


You have to pick the materials you use to build the P-N junction, this determines the band gap

To tune it for a longer wavelength (lower energy photon) you need a lower band gap.

This is all fine and good however we are limited in the materials we have, and a photon with more energy than the band gap energy does not produce more power it just produces more heat.

"Why can't we choose a material with a really low band gap, so we can use more of the photons? Unfortunately, our band gap also determines the strength (voltage) of our electric field, and if it's too low, then what we make up in extra current (by absorbing more photons), we lose by having a small voltage."

nothing is ever easy


Allen Zheng, I like your thinking. Even better would be to choose to target a 25% reduction in consumption in the next 20 years. Can you imagine that?


This looks like a candidate for use with reflective solar concentrators as the energy source. Interesting!


How does this technology compare to the technology behind the old vacuum tubes?


The Vehicle Research Institute at Western Washington University did some work with a thermophotovoltaic powered electric car starting in the mid 90s. It used a 10 kWhr battery as a buffer between the thermophotovoltaic power plant and the electric motor.

They only claimed 7% efficiency for the thermophotovoltaic power plant, though. Not 40-50%.


Layman's comment; A similar technology is currently being marketed and run in diesel long haul rigs to eliminate the alternator for fuel efficiency. It replaces the muffler on the exhaust stacks. Probably not nearly as efficient, of course


There was a story on here about engine heat and thermoelectric semiconductors a while back. The impression I got was that the efficiency was in the single digits. Even though most of the energy used in an ICE goes out as heat, until the conversion efficiency goes up, it may not be very cost effective.


Re: Layman's comment;

Where can I read about this similar technology that is currently being used on long haul stacks?

Carlos Barrera

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Luke Frohling

It seems they MAY use it in their automobiles. I live in Tokyo and I will attend a press conference at Toyota Head Office on the 16th of June (2006) to discuss it. I will do more research to be sure. If anyone is interested or can give me additional information please feel free to contact me ;)

My address is lfrohling zero one at yahoo dot com dot au

Luke Frohling

Ron Vines

Interesting, where can I learn more? I would like to study pv concepts. I'm currently an engineering student with a devoping fondness of physics.

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