Shade on your solar panel can void your warranty

svetz

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A lot of panel warranties are voided by being improperly installed - no surprise... except that by improper they include excessive shading. The bypass diode's purpose is to prevent damage caused by shading. But, the current flowing through the diode shortens the diode's life, and if it fails the heat buildup can kill the panel.

From the LG warranty:
Improper installation or reinstallation and poor solar system design. (Examples of improper installations and very poor system design are modules installed in conditions which put long term stress on the bypass diodes in the modules, and also reduce the system output for the owner – for example prolonged significant strong shadowing of the modules e.g. via trees, walls, gables, overhangs, valleys, chimneys, satellite dishes etc (In such situations a professional solar designer will suggest a micro-inverter or optimiser solution and with such a proper solar system design solution the module warranty is fully applicable).
 

TCgreg

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I contacted a vendor for the hightec 200 watt panels asking about bypass diodes. This was their response:


Sorry for the delay, we have spoken to Hightec.

Hightec Solar is the actual manufacturer of the panels (I have personally visited the factory).

Here is what they explained to me. The bypass diodes are actually clipped inside the junction box (basically not being used). Here is why.

When panels are connected in series, the polarity is naturally changed. This causes the diode to start to carry current and that causes fire issues (it has literally happened with other manufacturers in the past). Therefore, Hightec clips the connections to the diode so that this does not occur (becuase they know that many people will connect the panels in series).

Did that answer your question?



Thanks,




Matt Dalley
President/CEO
Continuous Resources, LLC
 

svetz

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That's pretty crazy. It seems to be saying, we put diodes in because we like adding to the costs and need to claim we have diodes for the marketing; but we cut them so they don't work and will let your panel die from overheating so we can make even more money selling you replacement panels.
 

TCgreg

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That's pretty crazy. It seems to be saying, we put diodes in because we like adding to the costs and need to claim we have diodes for the marketing; but we cut them so they don't work and will let your panel die from overheating so we can make even more money selling you replacement panels.
It didn't make sense to me either. I noticed in some advertising the say "panels have the same diodes as everyone uses" They don't mention that they are useless.

My own 2 year old Grape 180 watt panels have diodes but according to GrapeSolar they are blocking diodes. This explains why I had poor results running the panels in series. One of the advertising features of these panels was diodes to help in shaded conditions. They have since changed to wiring them as bypass according to Grape.

My first camper had Renogy 100 watt panels. Putting them in series gave poor results when any shading was introduced. They had diodes, not sure if they were blocking or bypass.

I highly recommend people do their own testing if they are going to be using their panels in a mobile application where shading will occur and see how well any advertised "diodes" work. So far I am batting zero. In parallel my system performs well in full sun and in partial shade. IMO it's worth doing your homework and test them out for the kind of conditions you will experience.
 

Rider

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I'm wondering about US regs. All solar panels sold in the US has to have them. While technically, they do, they do not function, so is that a violation of US sales? UL?
 

MrNatural22

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It didn't make sense to me either. I noticed in some advertising the say "panels have the same diodes as everyone uses" They don't mention that they are useless.

My own 2 year old Grape 180 watt panels have diodes but according to GrapeSolar they are blocking diodes. This explains why I had poor results running the panels in series. One of the advertising features of these panels was diodes to help in shaded conditions. They have since changed to wiring them as bypass according to Grape.

My first camper had Renogy 100 watt panels. Putting them in series gave poor results when any shading was introduced. They had diodes, not sure if they were blocking or bypass.

I highly recommend people do their own testing if they are going to be using their panels in a mobile application where shading will occur and see how well any advertised "diodes" work. So far I am batting zero. In parallel my system performs well in full sun and in partial shade. IMO it's worth doing your homework and test them out for the kind of conditions you will experience.

I am also using Renogy 100w mono panels and was curious about the diodes they use. I was told by tech support Renogy panels have always used by-pass diodes and they do not have blocking diodes because most charge controllers prevent power from feeding back into the panels. I have three 100w mono panels in series and they perform well even in partial shade or clouds I still have 30-45volts coming out.
 

efficientPV

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Clipping diodes. Hope none of you are doing that. This is what happens when lawyers do design work. They are worried about fire in the junction box. It starts with the diode burning up, some arcing, connectors getting loose and adding more heat. It is pure legal reasons. I have some older 80W panels, SHARP I think. They had a diode chip mounted on a 1 inch piece of copper with ultra thick foil to get rid of even more heat. If you buy a 10A diode or 45A diode they will produce about the same amount of heat. The temperature will vary depending on the surface area to dissipate it. So, they went cheap on the diode and shading may cause unfortunate things to happen. Removing the diode pretty much eliminates the fire possibility. Except now you destroy the weakest cell from reverse voltage. You may not even notice it. Older panels often had hot spots that were visible. These were shorts, but week ones. The panels still worked with just a little lower output. Enough times creating these shorts and there is is a big drop in power. But, they won't be around to honor the warranty. I had a better picture of this cut open, but you get the idea. This was a lightning strike on the panels.001.jpg
 

TCgreg

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I am also using Renogy 100w mono panels and was curious about the diodes they use. I was told by tech support Renogy panels have always used by-pass diodes and they do not have blocking diodes. I have three 100w mono panels in series and they perform well even in partial shade I still have 30-45volts coming out.
In a 12v panel there is most likely 2 zones. If you knocked out half of one panel I suspect you would have a series connection of 9v + 18v + 18v or 45 volts. About what you are seeing. What is the amperage drop? Bypass diodes *should* pass all amperage so you should be seeing 45v @ ~5.5 amps or about 245 watts in a perfect world with one panel being half shut down. This is the math than never worked for me in my testing. Finished wattage was less than taking the shaded panel off line completely. The shaded panel had a detrimental affect on the entire string where as in parallel only the shaded panel was affected and the remaining panels in good sun continued to perform as expected.

Here are a couple vids that are pretty much on par with my findings:


 

MrNatural22

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Right now it’s been raining all day with cloud cover. This is what I producing on the mt50 and Aili monitor with three 100w panels in series. If you look at weather radar pics you can see the storm coming thru this whole area east of Tucson.
 

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TCgreg

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Right now it’s been raining all day with cloud cover. This is what I producing on the mt50 and Aili monitor with three 100w panels in series. If you look at weather radar pics you can see the storm coming thru this whole area east of Tucson.
You have a great set up for testing. What happens if you cover a cell similar to the video I posted by Per? Ideally it would be better to test on a sunny day when the system is more optimally utilized. It looks like your array is producing 54v at 1.2 amps. Your MPPT is converting that to 13.7v at 4.7 amps or about 64 watts coming from your 300 watt array. That small number is to be expected on a cloudy day. It looks like your set-up is a fixed system vs. a mobile system? Absolutely how I would set up panels that aren't exposed to random shading.

I would be interested to see some shading testing on a sunny day. Thanks for taking the time to document!
 

gehowi

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When a panel is half shadowed you will not get cell damage because the current through all panels in series will drop to almost 0.
So there is not enough power to heat up any cell.
The worst case is only one cell that gets (partially) shadowed in bright sun. The cell becomes a resistor at high current, heats up very fast and fails. In the best case it’s shorted and you lose 10-20% power. You will never know if you don’t monitor the current.

Cells with only two busbars are more sensitive to shadow damage than 4-5 busbars. I never had damage to my 5 busbar cells and I had to replace panels with 2 busbars during summertime. 100W max output dropped to 70W max in only 1 day.
Not sure, but I think the power and heat is more spread through more bars.

Now I work with groups of 6 panels in series. So every group must deliver the same current at all times. If one cell gets shadowed, the current from this group drops immediately.
I made an MCU that compares the current from all groups and disables the shadowed group for 10 minutes. Then enables again and shut down if the current is still not equal until the shadow is gone.
I know immediately it there is any problem with a cell or panel and I never have to replace panels anymore. I get a message if there would be any shadow. Monitoring can save you a lot of money.

My experience with bypass diodes? Don’t rely on them! And if they are not the best quality Schottky diodes with very low forward voltage, they may heat up a lot.
 

Freddmc

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On my bus I have 3 100w Renogy panels in parallel. When not being used the bus is parked in a carport which fully shades two of the panels while the 3rd panel is exposed to sun for part of the day, Should I be concerned about damage?
 

gehowi

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@Freddmc ,
Of course you have to use blocking diodes for every panel, if not the sunny panel will feed the shaded panels and that's dangerous as well.
With blocking diodes the fully shaded panels do not deliver or get any energy so they can't be damaged.
For the partially shaded panel: if you don't draw current from it (charge battery etc) then no problem.
If more than 20% shaded, there is not enough current to heat up cells too far. But if only a few cells are shadowed in strong sun while charging batteries, sooner or later they will be defective.
 

Bob B

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Well ..... seems like there is a LOT more going on with shading than I thought. I had no idea shading could damage a panel. Gonna have to do more research especially about these maxim chips. I ANYBODY using them?
 
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