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Home > Archive > Alternative Power sources > December 2006 > Fan-cooled PV experiment
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Fan-cooled PV experiment
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| Loren Amelang 2006-12-17, 5:25 pm |
| After repairing a contact inside one of my twenty year old PV modules,
I set it out on the shallow roof outside my window for an in-circuit
test. Clear winter day, full noon sun, still air at 45F, panel lying
on its side with a cardboard carton propping it up to face the sun.
The carton was about one-third the length of the panel, and at a
significant angle, so one wouldn't think it would block much
convection airflow. The panel output was connected to a battery bank
in parallel with nine identical panels. As the panel warmed up in the
sun, I watched the output drop by about 33%.
I happened to notice a 110 CFM computer fan on the bench for another
project, and couldn't resist trying it out. I just set it on the roof
behind the panel, blowing lengthwise along the bottom portion of the
panel. Over about five minutes, the current output of the panel went
up by 25%! Without touching anything else, I unplugged the power to
the fan, and watched the current drop back by over 20%. By this time
some haze and a few puffy clouds had rolled in, reducing the heat of
the sun quite noticeably and ending the experiment.
The maximum gain was about half the power consumed by the fan, so I'm
not suggesting fans as the answer, but I'll certainly be looking to
create opportunities for convective airflow behind my PV array.
Has anyone here collected any similar data?
Loren
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| Vaughn Simon 2006-12-17, 5:25 pm |
|
"Loren Amelang" <loren@pacific.net> wrote in message
news:cldbo25d9f0cchuod77n2cfbs3jtvud1pf@4ax.com...
>
> The maximum gain was about half the power consumed by the fan, so I'm
> not suggesting fans as the answer, but I'll certainly be looking to
> create opportunities for convective airflow behind my PV array.
>
In the right climate (not mine) a bit of water mist might be a good idea.
Vaughn
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| Solar Flare 2006-12-17, 5:25 pm |
| I had my solar thermal panels pop a fitting and a 1/2" copper pipe
with a big Grundfos pump behind it pumping a steady stream of water
down a couple of PV panels from the eaves. Would that count?
LOL
"Vaughn Simon" <vaughnsimonHATESSPAM@att.FAKE.net> wrote in message
news:Awjhh.224020$Fi1.218188@bgtnsc05-news.ops.worldnet.att.net...
>
> "Loren Amelang" <loren@pacific.net> wrote in message
> news:cldbo25d9f0cchuod77n2cfbs3jtvud1pf@4ax.com...
> In the right climate (not mine) a bit of water mist might be a
> good idea.
>
> Vaughn
>
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| George Ghio 2006-12-18, 3:25 am |
| Loren Amelang wrote:
> After repairing a contact inside one of my twenty year old PV modules,
> I set it out on the shallow roof outside my window for an in-circuit
> test. Clear winter day, full noon sun, still air at 45F, panel lying
> on its side with a cardboard carton propping it up to face the sun.
> The carton was about one-third the length of the panel, and at a
> significant angle, so one wouldn't think it would block much
> convection airflow. The panel output was connected to a battery bank
> in parallel with nine identical panels. As the panel warmed up in the
> sun, I watched the output drop by about 33%.
>
> I happened to notice a 110 CFM computer fan on the bench for another
> project, and couldn't resist trying it out. I just set it on the roof
> behind the panel, blowing lengthwise along the bottom portion of the
> panel. Over about five minutes, the current output of the panel went
> up by 25%! Without touching anything else, I unplugged the power to
> the fan, and watched the current drop back by over 20%. By this time
> some haze and a few puffy clouds had rolled in, reducing the heat of
> the sun quite noticeably and ending the experiment.
>
> The maximum gain was about half the power consumed by the fan, so I'm
> not suggesting fans as the answer, but I'll certainly be looking to
> create opportunities for convective airflow behind my PV array.
>
> Has anyone here collected any similar data?
>
> Loren
Ah, another person who has learned a valuable lesson. Care must be taken
in the placement and installation of PV panels.
--
Posted via a free Usenet account from http://www.teranews.com
| |
| Vaughn Simon 2006-12-18, 9:25 am |
|
"George Ghio" <ghio@nobodyhome.com.au> wrote in message
news:4586345c$0$15521$88260bb3@free.teranews.com...
> Ah, another person who has learned a valuable lesson. Care must be taken in
> the placement and installation of PV panels.
So what do you do to keep them cool so that they will put out max power,
place them in the shade?
Vaughn
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| Loren Amelang 2006-12-18, 5:25 pm |
| On Mon, 18 Dec 2006 11:03:54 GMT, "Vaughn Simon"
<vaughnsimonHATESSPAM@att.FAKE.net> wrote:
> So what do you do to keep them cool so that they will put out max power,
>place them in the shade?
I'm thinking, as was mentioned in another thread a few weeks ago, the
back surfaces should be black for maximum radiative emission. Then
build a smooth-as-possible air channel along the back of each panel,
oriented as vertically as possible to maximize convection. In my case,
with a long single horizontal row of panels, the channels could
continue above the panels, painted black to create even more suction.
Too bad it seems all panels have frames that block straight airflow at
the top and bottom. Air isn't anxious to volunteer to turn sharp
corners... Assuming the long dimension is mounted vertically, I'd
think side rails about three inches deep, and minimal end rails, would
be about right. Mount those against a smooth surface and you've
created a cooling duct.
I wonder what you do when you have a rectangular array of panels,
though. If you connect the ducts in series, the top panels will start
with the heat from the lower ones. To create individual air inputs and
outputs for each panel, you'd probably need to extend both ends of
each duct to the edges of the array, which adds length and corners. I
suppose the best you could do is turn each input toward the back of
the array, and exhaust each output toward the front of the array,
through a space between the panel faces.
Just leaving large enough air spaces between your grid of panels might
help, even without the ducts. Presumably some cooler air from behind
the panels would move through and allow some of the heat to lift off
the faces of the array.
Anyone have access to a computational fluid dynamics program that
could visualize airflow around an array of panels?
Loren
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| Solar Flare 2006-12-18, 8:25 pm |
| How about air scoops (wings) like the back of the sporty cars to
redirect the air into the PV pan on the back? Sounds like long thin
squirrel cage fans at the bottom of each panel may pay off.
"Loren Amelang" <loren@pacific.net> wrote in message
news:vgqdo2tf79c7nddbjob7oihjedb31u9cp5@4ax.com...
> On Mon, 18 Dec 2006 11:03:54 GMT, "Vaughn Simon"
> <vaughnsimonHATESSPAM@att.FAKE.net> wrote:
>
>
> I'm thinking, as was mentioned in another thread a few weeks ago,
> the
> back surfaces should be black for maximum radiative emission. Then
> build a smooth-as-possible air channel along the back of each panel,
> oriented as vertically as possible to maximize convection. In my
> case,
> with a long single horizontal row of panels, the channels could
> continue above the panels, painted black to create even more
> suction.
>
> Too bad it seems all panels have frames that block straight airflow
> at
> the top and bottom. Air isn't anxious to volunteer to turn sharp
> corners... Assuming the long dimension is mounted vertically, I'd
> think side rails about three inches deep, and minimal end rails,
> would
> be about right. Mount those against a smooth surface and you've
> created a cooling duct.
>
> I wonder what you do when you have a rectangular array of panels,
> though. If you connect the ducts in series, the top panels will
> start
> with the heat from the lower ones. To create individual air inputs
> and
> outputs for each panel, you'd probably need to extend both ends of
> each duct to the edges of the array, which adds length and corners.
> I
> suppose the best you could do is turn each input toward the back of
> the array, and exhaust each output toward the front of the array,
> through a space between the panel faces.
>
> Just leaving large enough air spaces between your grid of panels
> might
> help, even without the ducts. Presumably some cooler air from behind
> the panels would move through and allow some of the heat to lift off
> the faces of the array.
>
> Anyone have access to a computational fluid dynamics program that
> could visualize airflow around an array of panels?
>
> Loren
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| Loren Amelang 2006-12-19, 5:25 pm |
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On Mon, 18 Dec 2006 18:59:06 -0500, "Solar Flare"
<solaerfart@hootmail.invalidated> wrote:
>How about air scoops (wings) like the back of the sporty cars to
>redirect the air into the PV pan on the back? Sounds like long thin
>squirrel cage fans at the bottom of each panel may pay off.
I suspect the air speed would be so low it wouldn't get much effect
from a "wing". But most of what I think I know about air movement is
from working with higher speed forced air. Now that I consider it, I
wonder if a CFD program could accurately model airflow at the low
speeds of convection around a PV array...
Speaking of fans, there was some kind of waving back and forth vane
fan proposed for cooling notebook computers a few years back. I seem
to remember it ran via stretching and shrinking of an "artificial
muscle" material, and was supposed to be quite efficient. Will have to
look for that idea...
Loren
| |
| Solar Flare 2006-12-19, 8:25 pm |
| Sounds very kinky too. Maybe look in the sex shops. LOL
"Loren Amelang" <loren@pacific.net> wrote in message
news:4bhgo29p2m0h9276cn4m06amcocl2d4mmf@4ax.com...
> Speaking of fans, there was some kind of waving back and forth vane
> fan proposed for cooling notebook computers a few years back. I seem
> to remember it ran via stretching and shrinking of an "artificial
> muscle" material, and was supposed to be quite efficient. Will have
> to
> look for that idea...
>
> Loren
| |
| Greegor 2006-12-22, 3:25 am |
| Loren Amelang wrote:
> the back surfaces should be black for maximum radiative emission.
Who said that and is there some physics explanation?
| |
| Loren Amelang 2006-12-22, 5:25 pm |
| On 21 Dec 2006 19:33:50 -0800, "Greegor" <Greegor47@gmail.com> wrote:
>Loren Amelang wrote:
>
>Who said that and is there some physics explanation?
Guess I did... "Should be black" is a non-technical way to say they
should have maximum emissivity. Emissivity relates the temperature of
a radiator to the amount of heat radiated.
<http://en.wikipedia.org/wiki/Emissivity>
Of course this also works in reverse, so if the backs of your panels
faced an even hotter substance, they would absorb more heat if
"black". But typically the panels will be hotter than their
surroundings, so it seems maximum emissivity would be an optimal
choice. Since emissivity works both ways, the same absorptive coatings
used for thermal collectors should be ideal for rejecting heat at the
backs of PV modules.
I've concluded the plastic backing material is typically white because
when PV panels were made of round cells with lots of space in between,
that space had to be white to minimize heat absorption from the front.
And even though the fronts of most panels are solid silicon by now,
nobody has thought to change the back color.
Anyone know of a reason not to go for "black"?
Loren
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| somebody@somewhere.com 2006-12-22, 5:25 pm |
| On Fri, 22 Dec 2006 14:28:36 -0800, Loren Amelang <loren@pacific.net>
wrote:
>Of course this also works in reverse, so if the backs of your panels
>faced an even hotter substance, they would absorb more heat if
>"black". But typically the panels will be hotter than their
>surroundings, so it seems maximum emissivity would be an optimal
>choice. Since emissivity works both ways, the same absorptive coatings
>used for thermal collectors should be ideal for rejecting heat at the
>backs of PV modules.
Why not just make a frame and stick a bladder full of water/antifreeze
in back that would form fit (mold to) the underside of the panel? a 1
x 4 frame, backed w/ a braced aluminum sheet painted black, and a 55
gal open black garbage bag full of water could provide significant
cooling during the summer. The top of the bag would be shielded on
the sunny side by aluminum flashing that rose 6" above the panel.
During the hottest (read sunniest) moments, the bag would
significantly lower the temp by absorbing excess heat and
thermosyphoning it upware beyond the panel. During colder periods,
the bag and panel would still be hot and release excess heat. At all
times, the hottest part of the bag and fluid would be above the panel.
Heat sink fins on the shaded side of the top could emit excess heat
continuously. At no time would the panel be exposed to the corrosive
effects of water. No moving parts, no fuss, cool.
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