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Published on September 5th, 2017 | by Tina Casey


Here’s A Diesel-Killing, Futuristic “Dip-Dry” Solar Device You Can Practically DIY At Home (Sort Of)

September 5th, 2017 by  

Record-breaking solar cells are exciting, but generating electricity from sunlight is just part of the solar energy equation. Another area with huge potential is solar thermal, which basically consists of harvesting heat from the sun and — well, that’s about it. You get heat, not electricity.

Solar thermal technology can be almost laughably simple — after all, you can DIY your own rooftop solar water heaters and water disinfectors out of plastic bottles. The technology gets much more interesting — and expensive — up the scale when concentrating solar power plants are in the conversation.

The challenge is to combine simplicity, low cost and small scale with high efficiency, and it looks like a team of scientists at Columbia University are on to a solution.

The selective solar absorber (SSA) developed by the researchers appears black, and thus absorptive, under sunlight (as shown on the photograph on the left). However, for thermal radiation, it behaves like a non-emissive metal mirror (reflecting the dark blue sky, as shown on the thermograph on the right), and prevents the absorbed solar energy from being radiated away and lost.

Solar Thermal Technology And Plasmonics

FWIW that’s plasmonics, not to be confused with The Plasmatics. Two totally different things.

Plasmonics refers to the plasmo-electric effect. When light reacts with certain metals, the result is plasmons or “excited” electrons. These electromagnetic pulses are kind of like waves of sound but not.

Our sister site PlanetSave offers this explanation of the challenge via Duke University:

Typically, plasmonic devices involve the interactions of electrons between two metal particles separated by a very short distance. For the past 40 years, scientists have been trying to figure out what happens when these particles are brought closer and closer, at sub-nanometer distances.

If you can leverage the plasmonic effect, you can bump up the efficiency of your device, because you can harvest more heat from a wider range of the light spectrum. The problem is how to get to that magic moment without breaking the bank.

The Road To Plasmonic Solar Thermal

So, what now? The new research from Columbia Engineering is an especially significant development because along with the increased efficiency and smaller scale it offers a more simple, environmentally friendly way to manufacture solar absorbers.

If you want all the details down to the nanoscale, check out the research team’s study, published in the journal Advanced Materials under the title, “Scalable, ‘Dip-and-dry’ Fabrication of a Wide-Angle Plasmonic Selective Absorber for High-efficiency Solar-thermal Energy Conversion.”

For those of you on the go, it boils down to a super special coating:

The authors determined that the plasmonic-nanoparticle-coated foils created by their method perform as well or better than existing SSAs [selective solar absorbers] and maintain high efficiency throughout the day, regardless of the angle of the sun, due to the wide-angle design.

High efficiency solar converters are already a thing, but they are expensive. The Columbia Engineering team focused on cost:

Most SSAs are made using more sophisticated, energy-expensive, or hazardous manufacturing processes such as vacuum deposition or electroplating. This increases both the environmental footprint and cost while limiting their accessibility.

Rather than going that route, the Columbia team took strips of foil and did this:

By dipping strips coated with a reactive metal (zinc) into a solution containing ions of a less reactive metal (copper), solar-absorbing nanoparticles of copper can be easily formed on the zinc strips by a galvanic displacement reaction.

As for the DIY angle, here’s lead author Jyotirmoy Mandal on that topic:

The beauty of the process is that it can be done very simply. We only needed strips of metals, scissors – to cut the strips to size, a salt solution in a beaker, and a stopwatch to time the dipping process.

The process is so simple that it would seem that you’d lose some efficiency, but no:

With its wide angle, the SSA addressed another long-standing problem faced by solar-absorbing surfaces: the ability to absorb sunlight throughout the day from sunrise to sunset. In tests, the resulting SSAs showed a significantly higher solar absorption at all angles (~97% absorption when the sun is above, ~80% when near the horizon) than existing designs.

So far, so good.

Next steps include testing additional materials with the aim of increasing efficiencies.

More bad news for diesel — and gas, too

All of this spells more bad news for the oil and gas industry. Before he was tapped US Secretary of State, former Exxon CEO Tex Tillerson vigorously promoted diesel and natural gas as the only way out of “energy poverty” for developing countries.

Well, it looks like Tillerson is a day late and a dollar short. In the age of next-generation solar efficiency, diesel and natural gas are as much out of date as coal.

Fossil fuels labor under two major disadavantages, aside from the obvious environmental problems: devices powered by fossil fuels require continuous outlays of cash to fuel up, and they require transportation networks, too — ships, roads, bridges, pipelines, storage and loading facilities and whatever else is necessary for Earth-bound fuel transportation.

In those respects, solar equipment wins handily. Once the equipment is in place there are no more transportation issues and no need to refuel.

The basic problem is cost, and the Columbia team is anticipating that their new system can eventually yield solar devices that off-grid communities can afford.

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Photo (cropped): Jyotirmoy Mandal and Yuan Yang / Columbia Engineering.



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About the Author

specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.

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