Back feed for snow melting?

[cmack]

Snow is really killing my solar buzz. Is it possible to back feed into the panels to heat them up without creating a fire hazard? Or any other solutions aside from a brush? My roof is way too high for me to reach so I need to find another solution!

 

[brum]

Gardening hose with warm water?

There are protective diodes that will bypass the panel if there is current in the forward direction. And the cells themself act as a diode in the other direction. So if you apply forward current - it will bypass the panel and if you apply reverse - it will not flow.

With proper installation, snow should not be an issue. If it is an issue for you it is likely that your panels are a bit too horizontal.

 

[cmack]

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.

With proper installation, snow should not be an issue. If it is an issue for you it is likely that your panels are a bit too horizontal.

My roof is actually quite steep. On regular snow days, it does tend to slide off on its own. We recently got a dumping of 25-30" so they didn't see the sun for over a week. Luckily we got some warm weather for a couple weeks so it's all gone now, but I don't really want to rely on luck.

 

[SparkyJJO]

With proper installation, snow should not be an issue. If it is an issue for you it is likely that your panels are a bit too horizontal.

Um, snow will stick to panels at the correct solar angles very easily. Heck, snow will stick to vertical things too (look at road signs that are facing the prevailing winds when a snowstorm hits).

 

[NEpowerandlight]

12v heat tracing cable around the panel frames?

 

[cmack]

12v heat tracing cable around the panel frames?

Not a bad idea. I wonder if it would be enough to keep the entire panel warm or just the edges? I may have to experiment with that.

 

[RCinFLA]

You could theoretically push a DC voltage approaching Voc to cause current to flow through the full cell inherent diode warming up cells. You would have to ensure you don't overdo it with the current but should be fine if you don't go much higher than Isc rating of panel.. Realize a panel open unloaded in full sun has the Isc current shunted down the inherent PV cell body diode so the cells can take the current flow.

Trick is as you melt the ice/snow off panel, the illumination current starts to add to any forced current you apply so forced current needs to back down to prevent too much dissipation in PV cells. The actual weak link is the cell surface current collector metal runners, not the silicon cell itself.

Also takes a lot of power so not very efficient.

With thick snow you may melt snow directly against panel creating a cavity between panel and surface thick snow buildup. Hopefully at some point all the built up snow just slides off the panel once base snow against panel surface melts.

A safe approach would be to force a current at a lower percentage of Isc. In the winter months with low sun angle above horizon it is unlikely full illumination will come anywhere close to rated Isc of panel so illumination current plus forced current should be safe.

 

[NEpowerandlight]

Not a bad idea. I wonder if it would be enough to keep the entire panel warm or just the edges? I may have to experiment with that.

It's interesting but in really cold temps I wonder how well it would work being exposed? I believe it works pretty good if it's insulted for keeping pipes from freezing.

I'd like to use it as deicing cable for my mini splits.

 

[efficientPV]

It has been done and it takes a LOT of power. I tried it with panels near freezing with jst a dusting of snow. It became clear the power needed would not offset additional power gained. If on each panel one section of cells was isolated with an additional lead, clearing just a spot to have a small section of panel become exposed to start solar melting could be a possibility. This is a pipe dream.

 

[Danke]

Install windshield wipers on them.

I use these guys’ service:

?

 

[cmack]

It has been done and it takes a LOT of power.

What sort of power was required in your experiment?

Lets say 1 500w panel takes 5kwh to melt snowfall over a 5 hour period. That loss would be recovered with 10 hours of sun (realistically 20 hours factoring in tilt, exposure, etc). If the snow was not melted, that panel could stop producing for weeks.

 

[Hedges]

I haven't tried melting snow, but I have tried backfeeding PV panels.
Every cell is a diode, and it operates forward-biased, not reverse biased.
One illuminated PV panel connected in parallel with one side a dark room didn't drive enough current to do anything interesting.
With two panels wired 2S placed in full sun, paralleled with a single panel in dark room, the current flowing through the dark panel was about 0.4 x Isc. In the case of my 165W panels, about 2A at 41V or 82W dissipated.

Measuring PV panel performance

I suppose I could buy a solar panel tester like Will reviewed, but that doesn't feel DIY enough to me. Besides, I'm a cheapskate, and I try to do things in the most difficult (and expensive if the equipment wasn't on hand) way. I'm presently working on an underperforming string of Sharp 165W...

diysolarforum.com

If you have a power supply to deliver Voc to your array or to a string, at 40% of rated wattage, that could work. (may be a tall order)

We do have to stop and think whether portions of the array could be damaged, especially when parts of the array clear as described by Efficient, resulting in power and temperature not being evenly distributed.

What sort of power was required in your experiment?

Lets say 1 500w panel takes 5kwh to melt snowfall over a 5 hour period. That loss would be recovered with 10 hours of sun (realistically 20 hours factoring in tilt, exposure, etc). If the snow was not melted, that panel could stop producing for weeks.

Save soot and apply to face of panels with a blower (to more efficiently absorb light)?

 

[cmack]

We do have to stop and think whether portions of the array could be damaged, especially when parts of the array clear as described by Efficient, resulting in power and temperature not being evenly distributed.

Maybe a dumb question, but during the meting process, would it help to shutoff the incoming PV?

 

[curiouscarbon]

never tested or experimented with this sort of thing.

heating up the dark edges of the panels seems somewhat promising too me in theory. melt only the snow on one edge, exposing dark metal. ideally sun would begin heating and melting more snow.

very interesting concept of automatically clearing snow with heat, but i have never heard of a working demonstrator.

good luck

 

[RCinFLA]

Maybe a dumb question, but during the meting process, would it help to shutoff the incoming PV?

You would have to disconnect SCC PV input as it will likely react to the applied defrosting power.

A good comparison for given area is power used for auto rear window defroster. They are typically in 100 watt range.

 

[OffGridForGood]

Perhaps best to apply the Voc before sun-up hopefully to break the frozen layer bond to the glass, let the snow slide, power off as the sun rises, let the sun finish the job. I got a free CSI 440 bifacial half cut, I will set up a test. If it blows up, I loose nothing, it was replaced for minor shipping damage.

 

[cmack]

Perhaps best to apply the Voc before sun-up

Good point. Much less likely to burn out components, easy to automate.

My panels Voc is around 47, I'm guessing I could branch off my 48v battery rack to the PV..how do you plan on applying voltage?

 

[OffGridForGood]

Bench source with voltage and amperage controls, have to check what i have to work with, compare to the panel spec (one panel for testing)

 

[OzSolar]

Save soot and apply to face of panels with a blower (to more efficiently absorb light)?

It worked excellent in my driveway a few years ago. I spread it around hoping for better traction with no idea how well it would melt the snow.

Once upon a time Midnite Solar had a snow melt feature in their charge controllers. Here's a short thread on it.

Midnite charge controller, snow melting mode questions....

How well does it work? im thinking of getting their top model now-250, thinking of upgrading next year my solar panel array.

forum.solar-electric.com

 

[SparkyJJO]

If I was needing to rely on my panels to be clear as much as possible I'd simply run some heat tape along the edges of the panels, or underneath them, or whatever tested out best, and then when they needed melted off I'd power it up to thaw things out.

This way it could be run at the same time the sun is shining and work in tandem with it.

Would be awesome if you could get panels with defrost grids built in, but that would probably be a cost up item that may or may not be worth it.

 

[PreppenWolf]

I haven't tried melting snow, but I have tried backfeeding PV panels.
Every cell is a diode, and it operates forward-biased, not reverse biased.
One illuminated PV panel connected in parallel with one side a dark room didn't drive enough current to do anything interesting.
With two panels wired 2S placed in full sun, paralleled with a single panel in dark room, the current flowing through the dark panel was about 0.4 x Isc. In the case of my 165W panels, about 2A at 41V or 82W dissipated.

Measuring PV panel performance

I suppose I could buy a solar panel tester like Will reviewed, but that doesn't feel DIY enough to me. Besides, I'm a cheapskate, and I try to do things in the most difficult (and expensive if the equipment wasn't on hand) way. I'm presently working on an underperforming string of Sharp 165W...

diysolarforum.com

If you have a power supply to deliver Voc to your array or to a string, at 40% of rated wattage, that could work. (may be a tall order)

We do have to stop and think whether portions of the array could be damaged, especially when parts of the array clear as described by Efficient, resulting in power and temperature not being evenly distributed.



Save soot and apply to face of panels with a blower (to more efficiently absorb light)?

View attachment 123815

This. We have a wood stove for all our winter heat. We spread the ash on the walkway to melt snow and ice.

 

[OffGridForGood]

I wonder if we will see combined PV/Solar hot water collection panels (Hydra-Solar) and if these would be more easily set up for snow melting; by running the hot water system to warm the panel enough to shed the snow. could be interesting.

 

[NEpowerandlight]

Roof de-icing cable burns about 8 watts per foot. How much would the shading from the cable effect the panels performance?

 

[RCinFLA]

I think it is worth a try to use the PV cells for heating. Watts is watts, whether it is amps squared x heater element resistance or amps x forward voltage drop across a PV cell inherent body diode. Cannot get a better thermal bond then the actual PV cells to front panel glass.

A full thermodynamic analysis is a bit difficult due to all the possible variables, particularly panel backside heat loss but based on rear auto window defroster wattage it seems feasible. The inside of auto window likely has less heat loss particularly since interior cabin heating is usually on at the same time.

If a 3' tall x 6' long (18 sq ft) auto rear window has 100 watt heat strip then a 3.5' wide x 5.5' tall (19 sq ft) PV panel would need same ballpark. Maybe multiply by 1.5 to 2x the required power to account for backside loss and/or speeding up the process.

Now if you are trying to clear 20 panels at the same time, that sums to a bit of power, but not out of reality. All comes down to power x time and an empirical real-world experiment would be good way to find that out. Maybe do one series string at a time so you can use cleared strings to help produce the power to clear the remaining series strings.

If you just melt base against glass surface creating an avalanche that would greatly help shorten time, so panel tilt angle plays an important role. That may mean more heating for shorter period of time creates the avalanche quicker, netting less overall kWh's needed. You just have to play with amount of heating power to find the optimum.

Putting a temp sensor on backside of panel behind middle of one cell would give good info to make power push to panel adjustments.

Power source needs to be a current limited supply. Voc is 100% current going through PV cell inherent diode. Vmp is only about 5% going through PV cell inherent diode, so actual voltage will be between these two points. As cell heats up its forward diode voltage drop decreases so a fixed supply voltage would cause an increase in current which is why you need a controlled current source.

 

[Hedges]

From my measurements, I think driving to about Voc is good, and will carry 40% of Isc.
I achieved that using 2s PV string in the sun paralleled with 1s PV panel in darkness.

Current limited sounds like a good idea. Slightly too high a voltage applied to forward biased diode (PV cell) could draw massive current.
Fuses for the string is a good backup, not sure that is sufficient to prevent damage (no fire is their job.)

How to do this is left as an exercise for the reader.
If able to freely rewire the array, would be easier. A boost converter may be the simplest retrofit.