Transparent, sprayable solar film developed at UCLA | Hacker News Reader

Transparent, sprayable solar film developed at UCLA

m.phys.org

54 pointsreplax8 comments

Odd mobile site repost of http://news.ycombinator.com/item?id=4772481 where there is discussion

If it captures infrared, could it be used to recover energy lost as radiating heat like house windows for example?

Could it be layered inside clothing, to generate power from body heat?

Trace amounts perhaps. Generally speaking radiative heat scales as T^4 where your temperature is measured on an absolute scale like Kelvin. In addition most of the heat flux being radiated by a human falls in the the 10um range which is somewhat difficult to detect and most certainly difficult to convert to electricity.

In short, think microwatts.

I guess there's more energy to be harvest from stretching and shaking your clothing while you move.

That's exactly the application they're after.

When these discussions happen I like to calculate some hard systems numbers since they're rarely in either the literature or the popular science articles. All the power available naturally comes from the sun so we need to know the solar spectrum to start. Conveniently there's an ASTM standard [1], so let's use that.

Here we're only interested in capturing energy outside the human visible spectrum so only radiation above 750nm is interesting.

Integrating from the spectrum data we find that the absolute maximum power that we can ever get from this system is 464W/m^2 (Compared to 1000W/m^2 without wavelength restriction)

The paper [2] talks about 4.5% PCE (power conversion efficiency), let's be generous and say they can get to 10% before commercialization which implies 46W/m^2 MAX from these window tints.

Since these films are on the sides of buildings we also can't track the sun. Solar angle varies throughout the day but let's integrate for a south-facing building in North American latitudes and we get a power factor of about 0.5 over the course of a day so we're back at 23W/m^2. of electrical energy from these films.

They're going to have to be exceedingly inexpensive to make this effort worthwhile.

[1] http://rredc.nrel.gov/solar/spectra/am1.5/ [2] http://onlinelibrary.wiley.com/doi/10.1002/adma.201203827/ab...

Very neat. It didn't really mention anything about production cost, but like most new and exciting innovations, it could be a huge barrier.

TL;DR

The title of the article contains all of the useful info in it. Very appropriate that it's a spray since it is likely vapor.

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