Groups > sci.electronics.design > #519080

Re: Can a small photocell panel be connected to a flashlight type rechargable battery?

From	Jasen Betts <jasen@xnet.co.nz>
Newsgroups	sci.electronics.design
Subject	Re: Can a small photocell panel be connected to a flashlight type rechargable battery?
Organization	JJ's own news server
Message-ID	<ppqsde$54m$1@gonzo.alcatraz> (permalink)
References	(1 earlier) <986vrddm75p51iimfob41mb9gvhpga930r@4ax.com> <ppoj5t$3ph$1@gonzo.alcatraz> <0k00sdt1dmep23fc5f6gcdnu6m89bjl52h@4ax.com> <ppp9tl$cpm$1@gonzo.alcatraz> <g8g1sddcro14rbn1rugn0396q4ke8lsqth@4ax.com>
Date	2018-10-12 19:24 +0000

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On 2018-10-12, Jeff Liebermann <jeffl@cruzio.com> wrote:
> On Fri, 12 Oct 2018 05:02:45 -0000 (UTC), Jasen Betts
><jasen@xnet.co.nz> wrote:
>
>>On 2018-10-12, Jeff Liebermann <jeffl@cruzio.com> wrote:
>>> On Thu, 11 Oct 2018 22:34:37 -0000 (UTC), Jasen Betts
>>><jasen@xnet.co.nz> wrote:
>>>
>>>>On 2018-10-11, Jeff Liebermann <jeffl@cruzio.com> wrote:
>>>>
>>>>> Well, try it.  You should measure the open circuit voltage and the
>>>>> short circuit current.  Don't leave the ammeter across the panel for
>>>>> very long or the panel might overheat.
>>>
>>>>They don't change colour in response to a load, open-circuit and short
>>>>circuit produce almost exactly the same self-heating
>>>
>>> Change color?  No, I didn't say that.  
>>
>>No, but assuming that conservation of energy is a law of the universe you
>>implied it. 
>
> Color me confused.
>
>>A shorted panel produces no power on the terminals. An open circuit panel
>>receives the same amout of energy from the sun as a shorted one (otherwise
>>it would change colour), so same temperature.
>
> A polycrystaline solar cell has an internal resistance of about 2 ohms
> which is easily measured.  When I short the terminals, the current
> produced is dissipated by this internal resistance.  P=I^2*R. However,
> with an open circuit, there is no current path through this internal
> resistance, therefore no self heating.  Most solar cells and panels
> have a Low-E coating on the glass cover designed to reflect IR and
> prevent heating of the cells by the sun which reduces the solar cell's
> efficiency.

Same energy in (full sunlight minus that reflected), same electrical 
energy out (nil). Therfore same amount of heating.  With the open circuit 
panel it's conduction through the diode junctions of each cell (hole-electron
recombination at the junction) that produces the same heat energy as the
resistive heating in the shorted panel, If you want to reduce the
self-heating of a panel electrically you connect it to a load (preferably MPPT)

Maybe they do change colour, the hole-electron thing could make
infared light...

Those coatings would also block some visible and near IR light that could
have been used by the solar cells, they would also trap more of the heat
produced by the visible light that isn't converted to electric current
and any heat produced by I^2*R losses.  I can seen them possibly being
useful on thermal solar panels (but ordinary glass is already pretty good at
blocking thermal inrared), but I am not convinced they'd help photoelectric
solar panels.

-- 
  Notsodium is mined on the banks of denial.

Thread

Can a small photocell panel be connected to a flashlight type rechargable battery? oldschool@tubes.com - 2018-10-11 00:32 -0500
  Re: Can a small photocell panel be connected to a flashlight type rechargable battery? <698839253X6D445TD@nospam.org> - 2018-10-11 06:10 +0000
  Re: Can a small photocell panel be connected to a flashlight type rechargable battery? tabbypurr@gmail.com - 2018-10-11 05:51 -0700
  Re: Can a small photocell panel be connected to a flashlight type rechargable battery? George Herold <gherold@teachspin.com> - 2018-10-11 06:18 -0700
  Re: Can a small photocell panel be connected to a flashlight type rechargable battery? dplatt@coop.radagast.org (Dave Platt) - 2018-10-11 10:39 -0700
    Re: Can a small photocell panel be connected to a flashlight type rechargable battery? bitrex <user@example.net> - 2018-10-11 22:41 -0400
  Re: Can a small photocell panel be connected to a flashlight type rechargable battery? Jeff Liebermann <jeffl@cruzio.com> - 2018-10-11 12:14 -0700
    Re: Can a small photocell panel be connected to a flashlight type rechargable battery? Jasen Betts <jasen@xnet.co.nz> - 2018-10-11 22:34 +0000
      Re: Can a small photocell panel be connected to a flashlight type rechargable battery? Jeff Liebermann <jeffl@cruzio.com> - 2018-10-11 19:31 -0700
        Re: Can a small photocell panel be connected to a flashlight type rechargable battery? Jasen Betts <jasen@xnet.co.nz> - 2018-10-12 05:02 +0000
          Re: Can a small photocell panel be connected to a flashlight type rechargable battery? gnuarm.deletethisbit@gmail.com - 2018-10-11 23:05 -0700
          Re: Can a small photocell panel be connected to a flashlight type rechargable battery? Jeff Liebermann <jeffl@cruzio.com> - 2018-10-12 09:08 -0700
            Re: Can a small photocell panel be connected to a flashlight type rechargable battery? gnuarm.deletethisbit@gmail.com - 2018-10-12 09:36 -0700
              Re: Can a small photocell panel be connected to a flashlight type rechargable battery? Jeff Liebermann <jeffl@cruzio.com> - 2018-10-12 10:20 -0700
                Re: Can a small photocell panel be connected to a flashlight type rechargable battery? gnuarm.deletethisbit@gmail.com - 2018-10-12 10:37 -0700
            Re: Can a small photocell panel be connected to a flashlight type rechargable battery? gnuarm.deletethisbit@gmail.com - 2018-10-12 09:41 -0700
              Re: Can a small photocell panel be connected to a flashlight type rechargable battery? Jeff Liebermann <jeffl@cruzio.com> - 2018-10-12 10:04 -0700
            Re: Can a small photocell panel be connected to a flashlight type rechargable battery? Jasen Betts <jasen@xnet.co.nz> - 2018-10-12 19:24 +0000
              Re: Can a small photocell panel be connected to a flashlight type rechargable battery? Jeff Liebermann <jeffl@cruzio.com> - 2018-10-12 18:26 -0700
                Re: Can a small photocell panel be connected to a flashlight type rechargable battery? gnuarm.deletethisbit@gmail.com - 2018-10-12 22:27 -0700
                Re: Can a small photocell panel be connected to a flashlight type rechargable battery? Jasen Betts <jasen@xnet.co.nz> - 2018-10-13 05:32 +0000
        Re: Can a small photocell panel be connected to a flashlight type rechargable battery? John S <Sophi.2@invalid.org> - 2018-10-12 02:12 -0500
          Re: Can a small photocell panel be connected to a flashlight type rechargable battery? gnuarm.deletethisbit@gmail.com - 2018-10-12 09:15 -0700
            Re: Can a small photocell panel be connected to a flashlight type rechargable battery? John S <Sophi.2@invalid.org> - 2018-10-13 15:14 -0500
              Re: Can a small photocell panel be connected to a flashlight type rechargable battery? gnuarm.deletethisbit@gmail.com - 2018-10-14 20:34 -0700
                Re: Can a small photocell panel be connected to a flashlight type rechargable battery? John S <Sophi.2@invalid.org> - 2018-10-15 20:39 -0500
                Re: Can a small photocell panel be connected to a flashlight type rechargable battery? gnuarm.deletethisbit@gmail.com - 2018-10-15 21:28 -0700
                Re: Can a small photocell panel be connected to a flashlight type rechargable battery? John S <Sophi.2@invalid.org> - 2018-10-16 18:08 -0500
                Re: Can a small photocell panel be connected to a flashlight type rechargable battery? gnuarm.deletethisbit@gmail.com - 2018-10-16 16:29 -0700
                Re: Can a small photocell panel be connected to a flashlight type rechargable battery? Jeff Liebermann <jeffl@cruzio.com> - 2018-10-16 16:47 -0700
                Re: Can a small photocell panel be connected to a flashlight type rechargable battery? John S <Sophi.2@invalid.org> - 2018-10-17 02:23 -0500
          Re: Can a small photocell panel be connected to a flashlight type rechargable battery? Jeff Liebermann <jeffl@cruzio.com> - 2018-10-12 09:23 -0700
            Re: Can a small photocell panel be connected to a flashlight type rechargable battery? gnuarm.deletethisbit@gmail.com - 2018-10-12 09:48 -0700
              Re: Can a small photocell panel be connected to a flashlight type rechargable battery? Jeff Liebermann <jeffl@cruzio.com> - 2018-10-12 17:57 -0700
                Re: Can a small photocell panel be connected to a flashlight type rechargable battery? gnuarm.deletethisbit@gmail.com - 2018-10-12 22:19 -0700
            Re: Can a small photocell panel be connected to a flashlight type rechargable battery? Jasen Betts <jasen@xnet.co.nz> - 2018-10-12 19:56 +0000
        Re: Can a small photocell panel be connected to a flashlight type rechargable battery? Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2018-10-12 07:36 +0000
          Re: Can a small photocell panel be connected to a flashlight type rechargable battery? George Herold <gherold@teachspin.com> - 2018-10-12 05:59 -0700
            Re: Can a small photocell panel be connected to a flashlight type rechargable battery? Jan Panteltje <pNaOnStPeAlMtje@yahoo.com> - 2018-10-12 13:06 +0000
          Re: Can a small photocell panel be connected to a flashlight type rechargable battery? gnuarm.deletethisbit@gmail.com - 2018-10-12 09:18 -0700
          Re: Can a small photocell panel be connected to a flashlight type rechargable battery? Jeff Liebermann <jeffl@cruzio.com> - 2018-10-12 09:44 -0700
            Re: Can a small photocell panel be connected to a flashlight type rechargable battery? <698839253X6D445TD@nospam.org> - 2018-10-12 17:57 +0000
        Re: Can a small photocell panel be connected to a flashlight type rechargable battery? whit3rd <whit3rd@gmail.com> - 2018-10-12 23:23 -0700
          Re: Can a small photocell panel be connected to a flashlight type rechargable battery? gnuarm.deletethisbit@gmail.com - 2018-10-13 04:56 -0700

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