Heating PV panels for snow removal?
D.A.Kopf
any damage could be caused by heating them through reversal of the connections
from the battery bank for a couple of hours. Would 50 watts per panel cause
any harm? The warranty is strangely silent on this question :)
Dorsai
Trying to feed power back into a panel probably isn't possible -
you've *probably* got a diode in there someplace to prevent the
batteries from discharging into the panel at night.
Your best bet would be to just clean a batch of snow off each panel,
and let the sun do it's thing - not only get a little power from the
panel, but let the sun heat the thing enough to let the snow slide
off (assuming the panel is tilted at least a little bit). Once the
sun can hit the panel, the panel will warm up enough to let the snow
slide off pretty quick. Ever noticed how fast snow/ice disappear from
a sidewalk or street once there's even a _little_ gap in the
snow/ice? Same idea.
I've got a panel I've been using as a test platform; before winter
came, I cleaned it real good and hit it with some Rain-X(tm). After
the snow stops, I just have to give the panel a quick sweep with my
hand and by the end of the first day of sunlight, it's clear - the
Rain-X(tm) keeps the snow from even *thinking* about trying to stick
to the relatively warm panel.
It's a little more work to prep the panel, but then I get that much
more power and efficiency out of it when I need it most (cold, dark
winter).
Dorsai
Jeff Stephens
batteries because the charge controller would prevent any power flow in
the reverse direction. Even if you are not using a charge controller
the blocking diodes will prevent or reduce the amount of power flowing
back into the panels.
A better solution would be to mount some rigid house insulation to the
back of the panels. (Without using any adhesive because you will want
to remove it for the summer) Mounting insulation against the back side
of the panel will pevent heat loss from the back side of the panel and
allow the panel to melt the snow off by heating up in the sunlight. No
rubbing, no buffing, no problem.
BTW: if your panels are in a location you have to worry about snow you
should also have them pitched up to about 50-60 deg to maximize the
amount of sun you catch on these short daylight hours. (location
latitude +5 to 15 degrees)
Happy collecting,
Jeff
--
Jeff
D.A.Kopf
>
> There would be no point in actually reversing the polarity on the
> batteries because the charge controller would prevent any power flow in
> the reverse direction. Even if you are not using a charge controller
> the blocking diodes will prevent or reduce the amount of power flowing
> back into the panels.
I'd disconnect the charge controller (easy to do, just unscrew an inline 30
amp fuse) and then alligator clip the panels to the batteries. There are no
blocking diodes in the panels, although 12 volts may not be enough to overcome
the forward bias of the 36-cell strings. But if I could raise the voltage
enough with another series battery, presumably there'd be a 0.6 volt drop
across each PV cell, and 0.6 watts of heating per cell, per amp of reverse
current. What would be the harm?
>
> A better solution would be to mount some rigid house insulation to the
> back of the panels. (Without using any adhesive because you will want
> to remove it for the summer) Mounting insulation against the back side
> of the panel will pevent heat loss from the back side of the panel and
> allow the panel to melt the snow off by heating up in the sunlight. No
> rubbing, no buffing, no problem.
Well, in fact the panels are the roof of a shed, so an interior kerosene
heater could have melted the snow in a couple of hours. Since snow isn't
frequent here, I don't need exotic or risky solutions, but I was just
wondering whether reverse currents could be an option for rapid clearing of
snow off PV panels.
DW
a lot towards allowing the snow to slip off. One neighbor put 1" foam board around
the edges of her PV panels down to the roof, to "catch the heat coming off of the
roof" to keep her panels clear. Her panels were set at the tilt of the roof about
40 degrees. If anyone tries this I would like to know if it works. I figured she
needed more insulation in her attic if it did.
N. Thornton
blocking diode, they just slowly drain current. Whether they would be
happy on 24v I dont know, but since they are just series PN diodes I
would think they'd be fine as long as they weren't heated too
much.Silicon can take 150 C no problem, but I don't think the glass
would survive 150 C on one side and 0 C on the other. You'd need to
take it easy temp wise.
I doubt the warranty would support hooking them onto 24v to heat them
up though! You can always try a small one if you want to.
Would the energy generated during the day after snow clearing outweigh
the energy used to claer them? I wouldn't be surprised, who knows.
Bruno GARNIER
do.
To me, the diodes are not "blocking" the tyny night reverse current, but to
ensure that a cell-or a line of cells-doesn't become a current consumer, as
the temperature it can get can damage the encapsulating material (EVA).
I am going to make tests on an old pannel to tell you what occurs.
The word of wisdom was From N. when he says
" Would the energy generated during the day after snow clearing outweigh
the energy used to claer them? I wouldn't be surprised, who knows."
Bruno
"N. Thornton" <big...@meeow.co.uk> a écrit dans le message news:
a7076635.0201...@posting.google.com...
Graig Pearen
as much as I do :-)
--
Remove the "nospam." from my e-mail address when replying.
Bruno GARNIER
they consume more current than they save, and I have never seen in my
country an installation running this kind of diodes.
I will check, as my voltmeter is the only person I believe in. If this
interesses you, I will give you the results.
The reference I have close to me is from a UNESCO course on photovoltaïc
conversion physics where Jean-André Roger says :
"It has often be said that the purpose of the diodes used in a photovoltaic
system was to avoid battery discharge in the cells network during the night.
In fact, the reverse current is very small and this loss is smaller than the
loss of the diode during the day."
Photovoltaïc solar energy,
Vol 1 : Photovoltaïc conversion physics and technology
If you have informations on this subject, I would be very gracefull to read
it.
Bruno
Bruno GARNIER
current through it.
It gets to the limits of my home ampermeter (1 ma)
This gives 15 mV, or 210 mVH during a 14 hours night (2 mn of 12W bulb).
Maybe this is not the case with other technologies, or with bigger pannels
I nead to make the same test with a more accurate ampermeter.
I'll give you the results
Bruno
D.A.Kopf
If the panel has a 36 cell string it would take ~20 volts to forward bias all
the cells into conduction. I've never seen the full passive I-V graph of a PV
panel on a semiconductor curve-tracer, but would guess the leakage is linear
below this voltage and rapidly exponential above it (and strongly temperature
dependent). Efficient heating might use a current-limited >25 volt supply,
perhaps a DC-to-DC converter running off the battery. Although if the panel
can be split, each 6 volt string could be fed directly from the 12 volt
battery, which would require either temporary rewiring or relay or FET
switching of the interconnects.
N. Thornton
diode certainly increases its total output, though by how much I dont
know. I expect rather more than the loss you quote.
Silicon solar panels make leaky diodes, which is why there is current
at well below 0.6v per cell. Diodes are anything but linear BTW.
Bruno GARNIER
They have all the accurate meters I miss.
I will make a more "scientific" test.
I will also look at the behaviour at low lighting, to see at what point
reverse current begins to occur.
I will keep you informed
Bruno
Gerry
NASA NEWS
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