Nuclear Agency Has The Hots For Solar Energy Windows

January 3rd, 2018 by Tina Casey

A research team at Los Alamos National Laboratory has come up with a formula for a double pane window that can generate solar energy, serve as shading, and provide insulation to boot. That’s particularly interesting because LANL is under the umbrella of the Energy Department’s National Nuclear Security Administration and it is tasked with “delivering science and technology to protect our nation and promote world stability.”

One Word: Quantum Dots (Okay, So Two Words)

The new LANL research leverages quantum dots, which are these:

Quantum dots are nanoscale particles of semiconductor materials. They’ve earned the moniker “artificial atoms” because their electronic properties can be precisely engineered, and because their behavior demonstrates unique behaviors when tasked with harvesting solar energy or giving off light.

Recall the earth-shaking effect of plastic on life in the 20th century, and that will give you an idea of what’s in store when 21st century materials science is applied to solar technology.

Like plastic, quantum dots can be a relatively inexpensive material to work with, because they can be applied in a solution. The low cost factor is what makes the LANL research especially promising.

How To Trick A Quantum Dot

Applying a layer of quantum dots to window glass sounds like an easy enough way to make a solar window, but there is a problem. Quantum dots tend to absorb some of the harvested energy instead of spitting it out.

The LANL team basically tricked their quantum dots into behaving more efficiently, by adding ions of manganese. When light hits the quantum dots it triggers the manganese ions, which propel it out. The energy level of the emitted light is too low for re-absorbtion.

That is just on the front side of the double pane. The back pane is coated with a layer of copper indium selenide quantum dots.

The two panels “split” the solar spectrum into two parts. Each panel handles its own part, resulting in greater efficiency. In effect, the two panes act like a multi-junction solar cell:

The higher-energy photons can generate a higher photovoltage, which could boost the overall power output. This approach also improves the photocurrent as the dots used in the front layer are virtually “reabsorption free.”

So far the two layers are just bouncing light around:

The front layer absorbs the blue and ultraviolet portions of the solar spectrum, while the rest of the spectrum is picked up by the bottom layer.

Following absorption, the dot re-emits a photon at a longer wavelength, and then the re-emitted light is guided by total internal reflection to the glass edges of the window.

That takes care of the heavy lifting. Solar cells packed into the window frame grab the baton from there, and convert the light to electricity.

The research team cites a solar conversion efficiency of just 3.1%, so it’s a good guess that some further improvements will be made before you can ask about those fancy new windows at your local window store.

For more details look up “Tandem luminescent solar concentrators based on engineered quantum dots” in the journal Nature Photonics.

Every Building Is A Power Plant

The new research demonstrates a key advantage of solar energy over fossil fuels: you can harvest it just about anywhere the sun shines.

That includes the built environment. Throw in some energy storage and smart grid controls, and you could transform an entire city into a dynamo.

Solar-harvesting building elements are already a thing (just ask Elon Musk). The main obstacle to widespread adoption is cost.

Here’s lead researcher Victor Klimov enthusing over the potentials:

“…these quantum-dot-based double-pane windows and even more complex luminescent solar concentrators offer a new way to bring down the cost of solar electricity. The approach complements existing photovoltaic technology by adding high-efficiency sunlight collectors to existing solar panels or integrating them as semitransparent windows into a building’s architecture.”

Don’t just take his word for it. CleanTechnica has been following the solar window company New Energy Technologies, which had this to say in its 2017 year-end report:

By some accounts, this is the single greatest breakthrough in the $100 billion glass industry since Alastair Pilkington developed the float glass method of production in 1952, by which 90% of all glass is made today.

NET has been working on its glass coating technology for a while now. The latest milestone was a real-world fabrication test on industrial scale autoclave equipment, so stay tuned.

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Image: via LANL.









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