

Transparent Solar Cell
© Yimu Zhao, University of Michigan

But perhaps there are better ways to squeeze a few amps out of your building skin.

Grid-tied solar power is really designed for the American dream: It works best at low suburban densities on top of nice big bungalows, preferably with no trees around to block the sun. No wonder real estate developers are now building it into the houses they sell.

In the cities, with taller buildings, the amount of roof available per square foot of area goes way down. That's why this new solar collector developed at the Michigan State University. is so interesting: It is totally transparent and can be built into windows. There have been other attempts to coat windows with photovoltaics, but they tended to change the color or transparency of the glass. Richard Lunt of the Michigan State tells Science Daily:


from patent applicationGoogle patents/Public Domain

Interestingly, the photovoltaics are not actually on the glass; instead. luminescent solar concentrators (“LSCs”) divert wavelengths invisible to the human eye through waveguides to the perimeter of the window, where the photocells are located. It's sort of a transparent gate that lets the light we can actually see and use through, while diverting the rest to the edges. (At least that's what I could figure out slogging through the patent here)

There are a couple of issues. Because it only diverts a portion of the spectrum and there are losses in the process, it's not very efficient, currently at about 1%. Fully optimized, it might reach 5%. According to Zach at CleanTechnica Conventional solar panels that you can put on your roof start at 20% and run up to 40% efficiency. So putting these in instead of conventional windows is not as effective as putting conventional opaque solar panels on the face of a building, which already is less than optimal for solar angles.

Our windows already are solar collectors.

In fact, since most of the electricity used in a building goes to air conditioning, far more energy could be saved by a small reduction in the amount of glass on a building than could ever be generated by these windows. They are an interesting idea but fundamentally, we should be turning the opaque spandrels and space between windows into solar collectors at far higher efficiencies and reducing the amount of vision glass.

First, build an efficient wall with no more glazing than is needed to reduce demand; Second, get some power out of the opaque parts; then, maybe, worry about pulling energy out of the glass. But it is really, a very distant third.

I worry that architects will continue to build glass towers and say "hey, it's a solar generating window" instead of building a proper efficient wall.

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