Back feed for snow melting?

[curiouscarbon]

Today I set this test up again, yes, at 40vDC there is nearly zero Amp - measured with an accurate meter 0.2 Amps, no wonder it took over an hour to clear one panel. So I swapped the bench source with a higher voltage unit, this one can go to 60vDC, but only 5Amps. Accounting for the temperature Delta, I calculated the Max Voc to be 54vDC, so set the bench source to this, and max Amps (5A) and connected it up, the panel drew 5.1A, this warms the panel much faster.
But to set this up 'full scale' on a 2S-3P arrary I would need a controlled power source capable to deliver 108vDC, 30A - I would have to build something to do this, I don't have any DC sources higher than 60vDC, -LiFePO4 batteries 34S? (series connect two 17S)
Meanwhile, playing with a single panel is one thing, risking six panels, not so sure about doing that!

thank you very much for the experiments and sharing the results. i commend your risking your panel to learn something. hats off to you. may your panels operate long time ?

i do not live in a snowy area, but this concept still is super interesting to mitigate the energy loss pattern that comes with snow accumulation.

 

[OffGridForGood]

thank you very much for the experiments and sharing the results. i commend your risking your panel to learn something. hats off to you. may your panels operate long time ?

LOL Thanks for the comments!
Not a tremendous risk, I have one free 'spare' panel - it had some minor frame damage during shipping and I got a free undamaged replacment - kept the damaged unit too, I tested it and naturally it works fine, so I use this panel as a test unit and move it around to different set ups. I did a test with this panel on a West Roof, and determined it would only be effective 7-8 months per year, do didn't use the West Roof. If I ever get a panel damaged at least I have a spare! (if I don't blow it up doing snow melting experiments that is).
My take-ways on snow melting with reverse powering the PV:
-It is not very effective at minus 4C, it will be far less effective at minus 20C or in windy conditions.
-A suitable power source will not be convenient to put together/control/monitor/ worry over.
-A small oil heater set under the tilted PV array "tented-in" with some cheap tarps would work faster, with less risk to the panels.
-Tenting the panels every November and removal once snow begins to melt in spring comes to mind as an option (but wind is bad for this idea).
-Greater tilt to the array leads to less snow/ice accumulation, may try vertical for Dec, see what happens. (1 array 60Degrees 1 vert, then monitor)
-Once it is good and cold, (Jan/Feb) nothing sticks to the panels, the problem is mostly during times when the panels are close to the freezing point.
If the array could tilt past 90-degrees, and tilt back to ideal angle during the sun hours each day, it could be self-cleaning.
If I had a good exposed unshaded south wall, I would try the vertical panel set up mentioned.

 

[brum]

With panels in parallel, there is a pretty high risk of getting current running through mostly one of the strings.

The hot panel (melted snow) will drop its max Voc. The pane covered with snow in parallel with it will still be at high Voc. If you have 2 panels in parallel and one is at Voc 45, while the other is at Voc 54 all the current will go through the 45Voc one.

So melt the snow on string-by-string bases.

And here comes the question - what we can use as a 400V constant current source .

 

[yabert]

And here comes the question - what we can use as a 400V constant current source .

What do you think about that? ?
400V DC battery, but can be complex/dangerous to access 400V.
I can plug my 400V Chevy Bolt battery to power my house, but it's tricky.

More realistically, an EV charger can be a good candidate to have 400V DC from 120 or 240V AC.

 

[Hedges]

And here comes the question - what we can use as a 400V constant current source .

String of PV panels.

 

[brum]

Voltage is easy. Here the grid is at 230V. Diodes, capacitors, and I have 320V DC. The problem is that limiting the current at that voltage is pretty challenging. A 100 ohm resistor will limit the current to 1-2 amps, so that would probably be the way to try it.

 

[SpongeboB Sinewave]

It can work but not guaranteed to work if too far below freezing and too much snow piled up on the array. It does take a lot of power and energy unless a light dusting. As for how much current, just do not exceed the series fuse rating of the panel, typically 15A or 20A.

Here is an animated GIF of one time I tried it on Kyocera 125 watt, 12V modules. Voltage was around 25V (just higher than Voc) and around 10 amps... Duration was around 3 hours or so. Panel on the right was un-powered. One thing that kept this from melting faster than it normally would have was that the panels were sitting in the snow and of course the snow from the unpowered panel. Mid 20 degree F temperature as I remember.

 

[Hedges]

Variac.
But it is still good to have current limiting.
I use one, often with a resistor in series, to test transformers at lower (or higher) voltage.

VARIAC VARIABLE TRANSFORMER Output voltage: 0-260V Model 1KVA 2KVA 3KVA | eBay

Max output power: 2KVA 240V. include a power cord with plug to connect to Italy. Max output power: 1KVA 240V. Max output power: 3KVA. Max output current: 4A. Max output current: 8A. Max output current: 12A.

www.ebay.com

100 ohm resistor? Look at heating appliances. They can handle the power dissipation.

 

[Casteil]

Gardening hose with warm water?

I tried the hose idea! Even standing on a ladder, I couldn't reach them with enough water to make a difference.

Not a great idea. Applying warm or hot water to cold glass and solar cells susceptible to fractures is a good way to ruin or at least shorten the lifespan of the panels.

 

[curiouscarbon]

Not a great idea. Applying warm or hot water to cold glass and solar cells susceptible to fractures is a good way to ruin or at least shorten the lifespan of the panels.

the thermal shock of that approach causes me to reject it. of course i won't complain much about others doing it. the high temperature gradient concentrated in a small area is of concern to me as well.

cheers

 

[brum]

100 ohm resistor? Look at heating appliances. They can handle the power dissipation.

More likely 10 x 100W 20ohm resistors in series. This will provide some current control. This will be my first winter with PVs and I'll decide on it in the summer. But if I go for this - I'll likely implement some automation. Measure the voltage over the first resistor and based on that switch FETs to bypass some of the resistors. This can easily be driven by a microcontroller.

 

[Supervstech]

Not a great idea. Applying warm or hot water to cold glass and solar cells susceptible to fractures is a good way to ruin or at least shorten the lifespan of the panels.

I hear this all the time, but I've never had any issues drizzling hot water on snow or ice covered windshields...
Now... I wouldn't dump a 5 gallon bucket directly on a frozen window, but if drizzled slowly on the ice buildup, the window doesn't see the warm water, it sees the melted surface temp...

 

[WattAboutThat]

Idea 01
I am very new but I have a few ideas that might work, having said that I do not have any experience, so use caution if try, please advise of any of these ideas work:

Idea 01:

Install a heating pad on the back of each panel, they probably make larger ones for some industry, say for farms etc.

Then connect them to an independent power source that you can control on and off.

If you want independent control get an X10 type remote controlled plug, that is addressable, and get one for each heating pad on each panel, so that you can specify which pad or pads to turn on as needed.

here is a youtube video of someone else experimenting with this concept:

 

[WattAboutThat]

Idea 02:

SOLAR - DIY Ice Melt
——
Recipe from Video (link below!
1/2 Gal of warm water
6 drops of dawn dish soap
2 ounces of IPA (alcohol)
——

create an automated sprayer
or manually controlled sprayer
like used on auto windshield for wipers
and spray on top solar panels
and let run down to melt snow

would need to test
that it does not harm panels
on an independent panel
over time

the sprayer could be a simple pvc pipe
that has those little spray nozzles like you
see on vegetable misters at the grocery store

and a pump to pump the home made
brine ice melt from a tank on the ground
to just above each column of panels

fill the brine tank, turn on pump, let the salt brine flow down the front of the panels

turn off once melted


link of a recipe from a news show

 

[WattAboutThat]

Idea 03:

Hydrophobic (water repelling) Glass Treatment



There are several brands and different chemistries. But this is a silicon based treatment, that reduces the adhesion of water molecules from the surface. Which should make the snow slide off more easily.



You may need to determine if the solar cells require UV light spectrum for functionality. I think I read somewhere that these treatments might block UV spectrum, but not sure.





here is a link to some info

but many other sources out there



——

https://carglassguru.com/the-best-windshield-water-repellent/

——

 

[curiouscarbon]

I hear this all the time, but I've never had any issues drizzling hot water on snow or ice covered windshields...
Now... I wouldn't dump a 5 gallon bucket directly on a frozen window, but if drizzled slowly on the ice buildup, the window doesn't see the warm water, it sees the melted surface temp...

Key is reducing thermal shock. Drizzling or reducing flow rate ought to keep the thermal gradient in check.

The fundamental concept behind the advisory from my perspective is related to coefficient of thermal expansion. Some materials have higher or lower coefficient of thermal expansion. Materials with a low value will generally be more resilient. Materials with higher value of coefficient of thermal expansion will generally be more susceptible to cracking with a sudden temperature change.

Thermal expansion - Wikipedia

en.wikipedia.org

Using the panel itself as a heat source is quite interesting to me as compared to applying water at some rate, for two reasons.

First, reducing water use. Second, applying power to the panels ought to generally result in near uniform heat distribution, which I expect to subject the panel to the least amount of thermal shock, expansion, cracking.

 

[curiouscarbon]

Idea 01
I am very new but I have a few ideas that might work, having said that I do not have any experience, so use caution if try, please advise of any of these ideas work:

Idea 01:

Install a heating pad on the back of each panel, they probably make larger ones for some industry, say for farms etc.

Then connect them to an independent power source that you can control on and off.

If you want independent control get an X10 type remote controlled plug, that is addressable, and get one for each heating pad on each panel, so that you can specify which pad or pads to turn on as needed.

here is a youtube video of someone else experimenting with this concept:

this idea is appealing to me because i am not sure what damage might result from applying power to the panels via their electrical connection.

drawback maybe the need to source separate heating pads, and additional wiring. hopefully the adhesive would hold for long time

thank you for sharing!??

 

[WattAboutThat]

Idea 04:

Use some large pvc pipe as an air duct, a row of duct under each row of the array, with exhaust vents, just below each solar panel, then use a heat source and a pressure fan (ie. some kind of small furnace), to simply blow warm air on the bottom of each panel until melted, then turn off.

It only has to get the panels above 32degrees F
long enough for the melted snow (water) to run off of the panels.

And this heat source could double as a heat source for battery area if close to panels

If not create a remote on off switch for heat source and blower.

That may be my last idea.

Other than you could combine these ideas.

ps - you could potentially use the pvc duct system, to cool the panels on a hot day, to increase output - just speculation

awaiting feedback
thx

 

[Casteil]

I hear this all the time, but I've never had any issues drizzling hot water on snow or ice covered windshields...
Now... I wouldn't dump a 5 gallon bucket directly on a frozen window, but if drizzled slowly on the ice buildup, the window doesn't see the warm water, it sees the melted surface temp...

It's not worth the risk.

 

[Supervstech]

It's not worth the risk.

Well, I've lived in SOUTH FRIGGIN DAKOTA for 3 years,and if you don't park in a garage, you will have zero chance of even getting in the car without several buckets of hot water...

I've heard it van Crack from uneven hearing, from cold glass getting flash heated, from imperfections in the glass causing cracks to form, from. Cracks in the glass growing etc...

Thousands of hot water uses... for decades... Zero cracks ever.

But yeah... NEVER pout massive amounts of hot water on.

I have also heard a sunbaked hot window can shatter from cold water use...

No experience with that one...
I did live in Tucson for a year though... just never washed the car.