

Solar energy that doesn't block the view - jrs235
http://www.sciencedaily.com/releases/2014/08/140819200219.htm

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mchannon
Although they still can give skin cancer, there aren't enough UV photons in
sunlight to produce a worthwhile amount of power. Highly doubtful anyone
serious would try to make this work with UV.

Infrared, on the other hand, has some power production capability (though
visible contains a much better resource). Even though we may only be looking
at 0.3V (high wavelengths have low voltages), we might be getting a few amps
with a square foot of this material.

Makes a lot more sense than other PV-related window technologies. They're
going to have to figure out how to cool the concentrator cells lest they cause
adjacent construction materials to catch fire with how hot they run. (I^2R
losses mean that these high current cells will be dumping a lot of heat per
watt generated).

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BrandonMarc
Care to elaborate on the other pv-related window technologies? I'm curious.

Last decade I followed news of XsunX and their Power Glass ... and it was like
following news of flying cars, or returning to the moon: a continuous parade
of stories, every single one saying "we're almost there, next year we'll
really have it ready!"

The concept of "Power Glass" was similar to the article here; the glass had
tiny PV technology buried inside, with the idea that skyscrapers with their
glass facades could generate their own power, along with any other building
using lots of glass in its skin.

I see XsunX no longer mentions Power Glass on their website [1]. Now it looks
like any PV manufacturer. You have to go back 8 years in the Internet Archive
to see it [2]. They were sure proud of this revolutionary technology ... 8
years ago.

Oh well. At least flying cars are showing [3] progress [4].

[1] [http://www.xsunx.com/](http://www.xsunx.com/)

[2]
[https://web.archive.org/web/20060705005757/http://www.xsunx....](https://web.archive.org/web/20060705005757/http://www.xsunx.com/)

[3] [http://www.terrafugia.com/](http://www.terrafugia.com/)

[4] [http://mavericklsa.com/](http://mavericklsa.com/)

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mchannon
Even though to the uninitiated it sounds like a no-brainer to cover windows
with solar panels, it turns out that what makes a solar panel effective is
that it converts the light to electricity and only lets through what it can't
convert (which, sadly, tends to be what you can't see).

Windows are useful because they let light through. Solar panels are useful
because they don't.

If you ended up with some sort of hybrid that let 50% of the visible through
and absorbed 50% of the balance, it would not be a very good window (too dim
or obstructed), and it would cost at least double what a comparable solar
panel would cost (per watt). You'd also take some hits to aesthetics and
efficiency (humans want reflective coatings on smooth window glass, solar
cells want antireflective coatings on textured low-iron glass).

Wiring up the windows would likewise add to the installation cost. Solar
panels produce their rated power facing somewhere between up and south (in the
northern hemisphere), and building windows almost never face in that
direction, making for an ever bigger hit to performance.

Installing panels on buildings can be a good idea, but not where the windows
go. Rooftops and south-facing walls are about it.

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crdoconnor
>Lunt said more work is needed in order to improve its energy-producing
efficiency. Currently it is able to produce a solar conversion efficiency
close to 1 percent, but noted they aim to reach efficiencies beyond 5 percent
when fully optimized. The best colored LSC has an efficiency of around 7
percent.

By contrast, conventional rooftop solar is about 18-23% efficient and you need
a whole roof of those (often more) to power your house.

I don't think this would provide more than a tiny trickle of electricity, and
probably at quite high cost.

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spingsprong
That percentage will probably be even worse than that, since windows aren't at
the best angle or position for solar panels.

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hrjet
You guys are missing the fact that current windows are losing all of the
energy incident on them. 5% is infinitely better than 0%.

~~~
crdoconnor
It's only infinitely better if the cost of installing these systems is zero.
It isn't zero.

Just about the only situation it would make economic sense to do this would be
if it were almost the same cost of regular glass, and you already had a PV
system set up with virtually all the wiring & inverters necessary already in
place (these are a significant cost - roughly 50% of a regular PV
installation).

Otherwise the cost simply wouldn't make it worthwhile.

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rukittenme
Would be very cool to use on a skylight. It would generate electricity and
heat your home! Put some blinds on the inside and block the light in the
summer time.

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guard-of-terra
When there's a lot of sun your home needs cooling, when it's cold there is not
much sun.

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Houshalter
If you filter out infrared light before it comes through the window, would
that help your air conditioning a significant amount?

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pif
It would help, no doubt, even if I cannot estimate how much.

OTOH, it would help as well if windows did _not_ filter IR radiation. You
know, a greenhouse works because glass is transparent to visible and near IR
radiation, but is quite opaque to far IR. Visible light is the peak of the
spectrum of solar e.m. radiation and its frequency is proportional to the
temperature of the sun photosphere (~6000 K). Visible and near IR radiations
traverse the glass, gets absorbed by objects and heat them. Part of this heat
will be re-emitted as far IR radiation, with a frequency proportional to room
temperature (~300 K), which is 20 times smaller than visible light. This
factor 20 is enough for the glass to turn from transparent to opaque. That's
why you can have a greenhouse, or simply a car with its windows closed, get
hotter than the surrounding atmosphere.

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adrianN
Actually, greenhouses work because they let the sun in but prevent convection
from cooling the heated surfaces. The stuff inside would need to get pretty
hot to put out enough IR to make much of a difference.

[https://en.wikipedia.org/wiki/Greenhouse_effect#Real_greenho...](https://en.wikipedia.org/wiki/Greenhouse_effect#Real_greenhouses)

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pif
This doesn't negate what I said. Preventing convection means that hot air
stays inside instead of being dispersed. But hot air does emit IR radiation,
and if that radiation could escape the air would get fresher.

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adrianN
In the wiki link that I posted an experiment is mentioned where they used rock
salt instead of glass to build a greenhouse. Rock salt is IR transparent, yet
the greenhouse got to nearly the same temperature. Hence IR transparency is
mostly irrelevant.

~~~
pif
Thanks for the link, that's interesting. But, please, have a look on this site
as well: [http://www.drroyspencer.com](http://www.drroyspencer.com).

