Friday, March 20, 2015

Transparent Solar Panels as Metaphor

"A fully transparent solar panel that could make every window and screen a power source."  This article (published in 2014) has been showing up quite a bit in my Facebook feed over the last couple of weeks. Apparently some researchers at Michigan State have come up with a technology that "could turn any window or sheet of glass into a photovoltaic cell".   Sounds attractive, right?

The words "transparent solar panel" should be enough to set off anyone's BS detector.  After all, "transparent" means that it lets light through without attenuation.  And solar cells work by converting light energy into electricity. In that case it's gone, used up.  To imagine that light can be both used for energy generation and let through unimpeded to illuminate my room is like imagining that I can pay for my dinner this evening with the dollar that I already spent on breakfast this morning.

Now the scientists who developed these materials are, of course, perfectly aware of this fact.  If you look at the paper (Zhao, Yimu, Garrett A. Meek, Benjamin G. Levine, and Richard R. Lunt. 2014. “Near-Infrared Harvesting Transparent Luminescent Solar Concentrators.” Advanced Optical Materials 2 (7): 606–11) you'll find that what they have actually produced is a material which gathers energy in the infrared region of the spectrum while letting visible light pass through more or less unchanged.  I can well believe that this is a significant technical development.  On the other hand, if you take a look at the solar irradiance spectrum (above) you will see that a substantial portion of the power of sunlight does lie in the visible region.  A "solar panel" which does not make use of this portion of the spectrum would be at a significant efficiency disadvantage right from the get-go (to say nothing of the other losses which might arise from the more complicated nature of the "reluminescent" process employed vis a vis conventional solar panels).

These caveats though have mostly disappeared in the ExtremeTech article which has been circulating on Facebook, which only manages to describe as "not probable" the idea that you could put one of these gadgets over your smartphone screen and generate enough power to run it indefinitely.  If violating the first law of thermodynamics now counts just as "improbable", it is hard to imagine any context in which ExtremeTech might feel the word "impossible" to be appropriate.

Why is the "transparent solar panel" idea - the ExtremeTech version, not the reality - so appealing?  I suggest because it is an almost perfect metaphor for the world envisaged by one strain of green optimism, one that many of us would devoutly wish to be true.  In this "bright green" world, growth, production and consumption would continue unabated, but they would be overlaid by an almost invisible skin of miracle technology - a technology that finally would empower production without pollution, growth without guilt, and consumption without check.

A  little thermodynamics is usually enough to puncture such dreams.  That does not mean that technological improvements are worthless or futile, of course.  I think it does mean that the idea that technological progress will enable us to continue "business as usual" is a delusion.

Image credit: Wikipedia,


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