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Thermoelectric efficiency boost is good news for solar



September 26, 2012 – Comments (4)

This post is a companion to last week's post: Thermoelectric Material Is the Best at Converting Heat Waste to Electricity - The idea is that since a PV cell can convert only a certain amount of the sun's spectrum (which is something Beta Voltaics are trying to solve btw) the uncoverted part gets absorbed by the cell thermally heating it up. The idea in this post is to take that absorbed 'waste' heat and covert it to electricity. Basically you would laminate thermoelectric material onto the back of the solar cells.

This would mean a huge efficiency boost for solar installations, making them that much more effective.


Thermoelectric efficiency boost is good news for solar
14:41 26 September 2012
Green tech
Sally Adee, technology features editor

For more than half a century, researchers have been trying to salvage the substantial amounts of waste heat lost in fossil fuel plants and combustion engines. Heat loss throws away 40 per cent of petrol energy through the car's exhaust, and two-thirds of coal energy from coal-fired power plants.

Their putative ability to mop up that lost energy has made thermoelectric materials a perpetual Cinderella technology. The materials use heat to create "free" electricity: current is generated when the temperature difference between the hot side (say, the exhaust) and the cool side (the ambient air) pushes electrons from one side of the material to the other.

In practice, however, thermoelectric materials reclaim at best only 5 to 7 per cent of the lost energy. Their efficiency - a material's ability to generate electricity for a given amount of thermal energy - is reflected in a figure called its ZT. For 50 years, researchers have struggled to push that number past 1.

The most straightforward approach is to coax a material to conduct electricity, while preventing the heat from migrating (because efficiency depends on preserving the difference between the material's hot and cold sides). That means decoupling electrons from phonons - a phonon is to heat transfer what an electron is to electricity. Essentially, a phonon is a quasiparticle that can be functionally thought of the vibrations that carry thermal energy.

In other words, let the electrons flow while stopping the phonons in their tracks. But they have been difficult to decouple. So thermoelectrics been relegated to applications of last resort, such as in space, where the small amount of energy they reclaim is worth the cost of the expensive materials.

Then, last week, researchers at Northwestern University, in Evanston, Illinois, published a paper in Nature which indicates that they've kicked the ZT from 1 to 2.2. They did it by disturbing the flow of three different wavelengths of the phonons, which allowed the electrons to pass while trapping the phonons in layers, which they compared to a Russian doll. Pushing the ZT to 2.2 bumped the overall efficiency up to 20 per cent.

Their work has tantalising implications for a far more consumer-friendly application: solar panels. Normally these can only metabolise the photons from the high-frequency part of the electromagnetic spectrum, meaning most of the sun's rays are lost as waste heat.

Use thermoelectric materials to harness the entire spectrum and your solar panel will get whopping good efficiencies. Charles Stafford, who works on materials that can disrupt phonon flow at the University of Arizona in Tucson, calls the new research "very exciting work".

4 Comments – Post Your Own

#1) On September 26, 2012 at 10:56 AM, Teacherman1 (< 20) wrote:

Another good find and post binve.

Every time I see one of them, I immediately start thinking of a company that I want to start to take advantage of the technology.

Then my old body moves a little, and the aches, pains, and creaks remind me of why I retired. :)

I guess I will just have to settle on checking out existing companies to possibly invest in, that might be able to take advantage of the "new find".

Keep them coming.

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#2) On September 26, 2012 at 11:44 AM, binve (< 20) wrote:

Thanks Teacherman! Will do!

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#3) On September 26, 2012 at 12:11 PM, chk999 (99.96) wrote:

Roofing materials that integrate PV and thermal electric stuff could be a barn burner. Since the roof is mostly wasted space, why not use it to generate power and cut the peak load needs? We still need baseline power for the cold still nights, but using less of it would be a good thing.

Thanks for posting these blogs about hopeful, useful technology. It counters some of the stuff from the doomers. 

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#4) On September 26, 2012 at 12:34 PM, binve (< 20) wrote:


Exactly. Instead of having a hot roof and cooling the house with lots of AC in the summer, let your room absorb solar energy that 'knocks down' most of the incoming heat load, and generate the electricity to run the AC to cool the reduced heat load in the house. Seems like a win-win. And with advancements in solar and TE, the straight cost analysis is already compelling. And on top of that, most electric companies in the West are offering deals where they pay the up front and installation costs for a share of the energy production over the life of the panels. 

This will be the real game changer for solar adoption. If the homeowner doesn't have to shell out money up front and gets a cost-savings, why wouldn't they? And with new technology advancements, more and more electric utilites with start doing this because they can make more money on that spread.

I am glad you like the posts, will definitely keep em coming!

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