Turning heat to electricity

MIT research points to a much more efficient way of harvesting electrical power from what would otherwise be wasted heat.

In everything from computer processor chips to car engines to electric powerplants, the need to get rid of excess heat creates a major source of inefficiency. But new research points the way to a technology that might make it possible to harvest much of that wasted heat and turn it into usable electricity.

That kind of waste-energy harvesting might, for example, lead to cellphones with double the talk time, laptop computers that can operate twice as long before needing to be plugged in, or power plants that put out more electricity for a given amount of fuel, says Peter Hagelstein, co-author of a paper on the new concept appearing this month in the Journal of Applied Physics.

Hagelstein, an associate professor of electrical engineering at MIT, says existing solid-state devices to convert heat into electricity are not very efficient. The new research, carried out with graduate student Dennis Wu as part of his doctoral thesis, aimed to find how close realistic technology could come to achieving the theoretical limits for the efficiency of such conversion.

Theory says that such energy conversion can never exceed a specific value called the Carnot Limit, based on a 19th-century formula for determining the maximum efficiency that any device can achieve in converting heat into work. But current commercial thermoelectric devices only achieve about one-tenth of that limit, Hagelstein says. In experiments involving a different new technology, thermal diodes, Hagelstein worked with Yan Kucherov, now a consultant for the Naval Research Laboratory, and coworkers to demonstrate efficiency as high as 40 percent of the Carnot Limit. Moreover, the calculations show that this new kind of system could ultimately reach as much as 90 percent of that ceiling.

Hagelstein, Wu and others started from scratch rather than trying to improve the performance of existing devices. They carried out their analysis using a very simple system in which power was generated by a single quantum-dot device — a type of semiconductor in which the electrons and holes, which carry the electrical charges in the device, are very tightly confined in all three dimensions. By controlling all aspects of the device, they hoped to better understand how to design the ideal thermal-to-electric converter.

Hagelstein says that with present systems it’s possible to efficiently convert heat into electricity, but with very little power. It’s also possible to get plenty of electrical power — what is known as high-throughput power — from a less efficient, and therefore larger and more expensive system. “It’s a tradeoff. You either get high efficiency or high throughput,” says Hagelstein. But the team found that using their new system, it would be possible to get both at once, he says.

A key to the improved throughput was reducing the separation between the hot surface and the conversion device. A recent paper by MIT professor Gang Chen reported on an analysis showing that heat transfer could take place between very closely spaced surfaces at a rate that is orders of magnitude higher than predicted by theory.  The new report takes that finding a step further, showing how the heat can not only be transferred, but converted into electricity so that it can be harnessed.

A company called MTPV Corp. (for Micron-gap Thermal Photo-Voltaics), founded by Robert DiMatteo SM ’96, MBA ‘06, is already working on the development of “a new technology closely related to the work described in this paper,” Hagelstein says.

DiMatteo says he hopes eventually to commercialize Hagelstein’s new idea. In the meantime, he says the technology now being developed by his company, which he expects to have on the market next year, could produce a tenfold improvement in throughput power over existing photovoltaic devices, while the further advance described in this new paper could make an additional tenfold or greater improvement possible. The work described in this paper “is potentially a  major finding,” he says.

DiMatteo says that worldwide, about 60 percent of all the energy produced by burning fuels or generated in powerplants is wasted, mostly as excess heat, and that this technology could “make it possible to reclaim a significant fraction of that wasted energy.”

When this work began around 2002, Hagelstein says, such devices  “clearly could not be built. We started this as purely a theoretical exercise.” But developments since then have brought it much closer to reality.

While it may take a few years for the necessary technology for building affordable quantum-dot devices to reach commercialization, Hagelstein says, “there’s no reason, in principle, you couldn’t get another order of magnitude or more” improvement in throughput power, as well as an improvement in efficiency.

“There’s a gold mine in waste heat, if you could convert it,” he says. The first applications are likely to be in high-value systems such as computer chips, he says, but ultimately it could be useful in a wide variety of applications, including cars, planes and boats. “A lot of heat is generated to go places, and a lot is lost. If you could recover that, your transportation technology is going to work better.”

Topics: Energy, Computing, Electrical engineering and electronics, Innovation and Entrepreneurship (I&E)


We have something called the "free watt" system that is heating our house. I am not understanding exactly how this works but as we use heat, the heat not being used, that would be wasted, is captured and thrown into the "system", so we generate "credit' in energy in this very efficient heating system.

Of course the engineers can explain this.

It's an idea that's coming and I believe this is definitely a "gold mine" and should be pursued.

when every current electrical equipment is working, it would produce wasted heat. MIT research points to a much more efficient way of harvesting electrical power from what would otherwise be wasted heat

Patent is a device to convert the form between electricity and heat.

It is amazing!

When summer commes,hot commes.

How about to convert the heat in house to electricity automatically?

please send to my email the details of how heat is beig turned to electricity.

My unpatented device the heat superconductor produces electricity from heat. You will find it described on http://www.freewebs.com/thtayl... Its Carnot cycle on a temperature entropy diagram is an oblong consisting of heat being absorbed at constant entropy and electricity being delivered at a slightly higher temperature and again at constant entropy.It thus has a high efficiency

can any1 explain me how heat is converted to electricity? is it possible to convert the heat produced by the normal home appliances ?

If you harvest anything why not harvest the wasted heat (not light) from the sun and design this thing on a larger scale to do so. We have a lot of heat here in Texas that we would love to have harvested.

Couldn't we use this technology to harvest the unlimited and wasted heat that is expelled around volcanoes?

Yesterday I was on a roof and noticed that dryers expel a lot of heat that is not captured. I wondered if there is a system to capture the expelled dryer heat and recycle back into the home? It is wasteful. If there was a filtration system that rerouted the moist, warm air back into homes it would cut down on energy to heat the dwelling and energy used to run humidifiers. (Plus, who doesn't like the smell of freshly dried clothes?) There are aproximately 100,000,000 households in the US that run dryers. A majority of these are in temperate climates. Isn't this the same principle, eliminate waste?

It's a nice idea but there is a safety consideration. From a safety standpoint, I know there are a couple of problems with some older dryers that produce carbon monoxide. If you're not worried about that, add a filter housing and a dryer hose attachment into the ductwork in your house instead of venting it to the outside. (run you roughly $70 if you shop around) If you do this, I suggest capping the dryer vent to the outside until summer, when you'd probably benefit from venting it outside.

You could harvest the mechanical energy as electricity with a rewired fan but you'd need a battery to use the energy. Given it's a mechanical system a power regulator wouldn't necessarily be required but it wouldn't be a bad idea. This would run a little closer to $200

I have at home a woodfired heater/cooker which normally burns overnight. Can the heat generated at night be used to create electricity? It has a large (hot) surface (which is the cook-top) and seems such a waste to not use the heat with some device sitting on the cook-top at night to produce the electricity which can (in Tasmania) be fed back into the normal household reticulation system (the Grid) for credits on the electricity account.

Any comments?

No you cant just run the air from you dryer back into your house, it has carbon di and monoxide (do to the combustion of your hydrocarbon). You could use some kind of radiator tho. Make sure it doesn't cause too much back pressure tho because your stuff won't dry and the gas might come out somewhere you don't want it. If it were electric then yes, you could.

The best application for this teck that I can think of would be the hot water expelled by nuclear power plants. very how water next to cool water. What more could you ask for?

The answer is no. You again are using a difference in temperature and again you would need something with a grate deal of thermal capacitance. The air in your house isn't going to cut it. Don't say something dumb ether like "you could use a heat sink and a fan". You won't get as much out of it as you put in... you might be able to use a metallic plate, painted black, in the sun and water in one of those geothermal systems.

Ok so I'm only 17 but I was reading a book and I thought of turning heat into energy, namely electricity, so I searched google and saw and read this. Now, if you took the percentage of electricity we can currently get from heat and put it to a bigger heat source wouldn't you be able to harness more energy than from small devices we have now? This brought me to the thought of clean renewable energy from the harnessed heat and made me ask myself, what if we just used what we have now on a volcano? They produce vast quantities of heat naturally, they are all over the planet and if it worked it'd just take slight changes to put into smaller objects like phones and laptops and such. Why start small and go big if u can start big and go small?

Is'nt this technology related to the solar panels that automatically converts heat(rays from the sun) into direct current? Can someone tell me how they are different, ie, what basically makes them different?

I've been waiting for an air conditioner which works more efficiently as the weather gets hotter by converting atmospheric heat to electricity.

can anyone of you tail me how much heat energy do we need to produce 1 volt

Mr. Hagelstein, do you use thermoelectric materials in your dream project? If so, there is a kind of plastic type of thermoelectric material that is less efficient, but very cheap and raw materials are abundant. I hope those can be useful. Lots of plastic products clogs the drainages here and pollute our rivers and seas. Our country used to be 20 degrees C colder than what is now. Sorry for my grammatical errors.

Nano technology is another route to turn heat into energy. Some devices are discussed at olsonb.com which generate electrostatic charges from plastic nano beads and then the electricity is captured in a capacitor. There is also Daniel Sheehan's technology (perpetual computing) which looks promising but is controversial as the second law becomes in question.

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