Re: charging solar cell

[Hactar]

In article <ep6ap81r2tneafrth...@4ax.com>,
Les Albert <lalb...@aol.com> wrote:
> On Thu, 16 May 2013 13:34:47 -0400, "Gus" <gus.o...@geemail.com>
> wrote:
>
> >Does it matter if a solar cell is indoor behind a glass window (which
> >filters out the UV)? I noticed my hand crank radio/led light had lost all
> >power (I had apparently left the radio on weeks ago) and would not come back
> >on, even after cranking it for a minute. Which made me very sad because it
> >is very handy when power goes out.... I put it outside under an overhang
> >(it has a solar cell on top) in hopes it would charge it. Though I feared
> >it was a goner. I thought maybe the rechargeable battery would have to be
> >replaced and was looking up how to email the company (Eton). To my
> >surprise, when I went outside (it is a cloudy rainy day) the radio came on
> >and the light works too! I had cranked it for a couple minutes earlier with
> >no luck, but leaving it off and in some daylight charged it after just a few
> >minutes.
> >To fully charge, it says to leave in direct sunlight. Don't solar cells
> >have glass on top? So they must absorb energy from other than UV spectrum?
> >The unit says to keep away from water, so I thought I would leave it by a
> >closed window that gets sun but would not allow it to get wet.
>
> "Solar cells are made out of N-type and P-type semiconductor material
> that use the visual light spectrum to generate electricity. Solar
> radiation with wavelengths of 380 nm to 750 nm (violet to red) strike
> the material with enough energy to knock electrons from their weak
> bonds and create an electric current. The unused wavelengths
> (ultraviolet & infrared) do not have enough energy to dislodge the
> electrons and are absorbed as heat." - http://tinyurl.com/bkcotvw

UV doesn't have enough energy but visible does? Sorry, that's not
possible. E=h*nu, where h=Planck's constant and nu=frequency. UV is
absorbed (by something) and wasted as heat? Entirely possible.

--
-eben QebWe...@vTerYizUonI.nOetP royalty.mine.nu:81
LIBRA: A big promotion is just around the corner for someone
much more talented than you. Laughter is the very best medicine,
remember that when your appendix bursts next week. -- Weird Al

[Paul Ciszek]

In article <4rsf6a-...@pc.home>, Hactar <ebenZ...@verizon.net> wrote:
>
>UV doesn't have enough energy but visible does? Sorry, that's not
>possible. E=h*nu, where h=Planck's constant and nu=frequency. UV is
>absorbed (by something) and wasted as heat? Entirely possible.

You are right that short wavelength photons carry more energy than long
wavelength photons. Here is the full story of what happens when a photon
hits a photovoltaic device:

Some photos just reflect off of the surface and do you no good. The
manufacturers try to minimize this with coatings.

Long wavelength photons with too little energy to free up an electron
will either pass through (if the semiconductor is thin enough) or be
absorbed in the ordinary, thermal way and become heat.

Shorter wavelength photons with enough energy might still be absorbed,
but at least some of them (and for very good devices, nearly all of them)
will temporarily free up an electron. (Actually, it's only "nearly free",
but I won't go there now.) These electrons make up the current generated
by the device. But here is the catch: The energy that can be harvested
from each electron is equal to the minimum required to free it up in the
first place; any energy above and behond that becomes more waste heat.
So, the same device might absorb some IR, most visible, and some UV photons.
but some of the energy in the visible ones and most of the energy in the
UV ones is wasted. In the case of Silicon, useful response starts a good
way into the IR, peaks at the red end of visible, and begins to roll off
by the time you get to blue. Since there is a lot less violet and ultra-
violet in sunlight than there is visible and infra-red, this works out
fairly well, and silicon solar cells are pretty common. (They also
get to ride the coattails of all the research done on silicon for other,
more expensive electronic devices.) Other materials, like Gallium
Arsenide, get more energy out of each photon, even if that means missing
some photons that Silicon would catch, but get more power per square
meter as a result. They are also more expensive to make.

I am simplifying and telling little white lies here, but if you want to
know more about this, there are courses you can enroll in.

--
"Remember when teachers, public employees, Planned Parenthood, NPR and PBS
crashed the stock market, wiped out half of our 401Ks, took trillions in
TARP money, spilled oil in the Gulf of Mexico, gave themselves billions in
bonuses, and paid no taxes? Yeah, me neither."

[Hactar]

In article <81lap8heh2hfebjsm...@4ax.com>,
Les Albert <lalb...@aol.com> wrote:
> On Thu, 16 May 2013 16:40:36 -0400, ebenZ...@verizon.net (Hactar)
> wrote:

> >Les Albert <lalb...@aol.com> wrote:
>
> >> "Solar cells are made out of N-type and P-type semiconductor material
> >> that use the visual light spectrum to generate electricity. Solar
> >> radiation with wavelengths of 380 nm to 750 nm (violet to red) strike
> >> the material with enough energy to knock electrons from their weak
> >> bonds and create an electric current. The unused wavelengths
> >> (ultraviolet & infrared) do not have enough energy to dislodge the
> >> electrons and are absorbed as heat." - http://tinyurl.com/bkcotvw
>
> >UV doesn't have enough energy but visible does? Sorry, that's not
> >possible. E=h*nu, where h=Planck's constant and nu=frequency. UV is
> >absorbed (by something) and wasted as heat? Entirely possible.
>

> But http://www.repairfaq.org/sam/sipdresp.gif

I'm not disagreeing with the results. They are what they are; you can't
argue with facts. I'm saying that aspect of their explanation is
technobabble. Maybe the UV is absorbed by something, or maybe it's not
close enough to the right energy to kick an electron up a level,
whatever. But "not enough energy" is right out.

[Snidely]

After serious thinking Hactar wrote :

> In article <81lap8heh2hfebjsm...@4ax.com>,
> Les Albert <lalb...@aol.com> wrote:
>> On Thu, 16 May 2013 16:40:36 -0400, ebenZ...@verizon.net (Hactar)
>> wrote:
>>> Les Albert <lalb...@aol.com> wrote:
>>>> "Solar cells are made out of N-type and P-type semiconductor material
>>>> that use the visual light spectrum to generate electricity. Solar
>>>> radiation with wavelengths of 380 nm to 750 nm (violet to red) strike
>>>> the material with enough energy to knock electrons from their weak
>>>> bonds and create an electric current. The unused wavelengths
>>>> (ultraviolet & infrared) do not have enough energy to dislodge the
>>>> electrons and are absorbed as heat." - http://tinyurl.com/bkcotvw
>>> UV doesn't have enough energy but visible does? Sorry, that's not
>>> possible. E=h*nu, where h=Planck's constant and nu=frequency. UV is
>>> absorbed (by something) and wasted as heat? Entirely possible.
>>
>> But http://www.repairfaq.org/sam/sipdresp.gif
>
> I'm not disagreeing with the results. They are what they are; you can't
> argue with facts. I'm saying that aspect of their explanation is
> technobabble. Maybe the UV is absorbed by something, or maybe it's not
> close enough to the right energy to kick an electron up a level,
> whatever. But "not enough energy" is right out.

"Not the right amount of energy" -- remember that this is a quantum
effect that depends on the band gaps, and it's pretty much illegal to
boost an electron to certain levels, which makes aborbing that photon
problematic.

/dps

--
Maybe C282Y is simply one of the hangers-on, a groupie following a
future guitar god of the human genome: an allele with undiscovered
virtuosity, currently soloing in obscurity in Mom's garage.
Bradley Wertheim, theAtlantic.com, Jan 10 2013

[Snidely]

After serious thinking Snidely wrote :

Much of the magic of the alloy recipes is tweaking the bandgap to be
useful for the purpose of the device, whether a solar cell or a
transistor gate.

/dps

--
But happiness cannot be pursued; it must ensue. One must have a reason
to 'be happy.'"
Viktor Frankl