As solar panels become more and more affordable, and as electricity prices increase, the best way to size a solar system is often to just “fill the roof with solar panels”. Naturally, this means panels are not always going to be installed in the most ideal location. Some solar panels will get shaded at certain times of the day, and produce less.
But, did you know that shading a panel can damage it? Here’s why.
Shade can damage a solar panel
When a part of a solar panel is shaded, it stops producing energy and starts consuming some energy from the other solar panels. This energy is dissipated as heat. If that shade remains on the panel for a long time it will create a hot spot on the panel, and it may damage the cell and the backsheet.
However, panels come with “hot spot protection”: a little device called a bypass diode, and each panel has three of them. The primary job of the bypass diode is to minimise the hotspot damage caused by shade. Here’s basically how it works:
When the solar panel consumes energy, it creates a reverse voltage. When that voltage reaches a critical point, the bypass diode will engage, or close. The energy from the other panels will then bypass the shaded cells before those cells are damaged.
However, if this shade happens too regularly, it may not only damage your solar cells, but the bypass diode could also fail.
How much shade can a solar panel handle?
Will too much shade void your warranty? If you look up just about any panel warranty document, it will say that if you don’t follow the install manual, you void the solar panel warranty, which sounds fair enough. So let’s look at the installation manuals.
I started by looking at what I call the best panel on earth, SunPower’s new 415 w MAXEON 5 panel. This panel comes with an Enphase microinverter attached to it. Pretty obviously the product was designed to be installed on shaded roofs. But exactly how much shade will Sunpower allow?
Let’s have a look at the install manual. It says:
“Shading needs to be avoided during the solar system operation.”
“The solar system should be turned off if there is maintenance on the roof which causes shading (e.g. chimney sweeping, roof maintenance or antenna installation).”
That would be hilarious if it wasn’t so pathetic. According to SunPower’s installation manual, not only do we need to avoid all shading from trees, but even if we jump up on the roof to clean the chimney, we need to turn the system off. And this is for the SunPower Max 5 solar panel. A panel made with a micro inverter built into it!
At MC Electrical we also install QCells Solar Panels. So I looked at the QCells Solar Panel installation manual hoping for some sanity.
QCells install manual is no better. It says we must:
“Avoid shadowing from buildings, chimneys or trees.”
“Avoid partial shading from overhead lines, dirt and snow.”
I then looked up a total of 10 different solar panel manufacturers’ installation manuals.
Every manufacturer said we must not install solar panels in partial shade. Except for REC, who said try to avoid shade, but if you can’t keep the shade to an absolute minimum.
The solar shade industry
So there is a whole industry within the solar industry built on the fact that solar panels are going to see some kind of shade. Optimisers, micro inverters and innovations like Fronius’s Dynamic peak manager and SMA’s shade fix. They are all made to help solar panels deal with shade.
Meanwhile, panel manufacturers are having a laugh amongst themselves. If shading really does cause damage to panels on mass, they will be able to wipe their hands clean of the issue. Their install manual clearly says not to install panels in the shade.
The looming solar panel disaster?
I wouldn’t be surprised if this turned out to be a solar industry disaster in 10 years. In the last 10 years, the solar industry has learnt so much. In another 10 years, the industry will have learnt so much more. Maybe we’ll find out how badly today’s thinly sliced solar cells react to just a little bit of shade. Maybe the quality installers of 2030 will be removing faulty panels thinking installers from 2021 were all a bunch of idiots for installing in the shade.
Or maybe it won’t be a problem at all. Who am I to know?
But let’s say your solar panels start failing in 2031. Maybe due to shade, maybe for another unknown reason. As your installer, I’ll try to get your panels replaced under warranty. But what if the manufacturer refuses to honour the warranty? They point out that Google Maps show the neighbour’s trees have grown and those panels are in partial shade in the winter.
You should have read the manual. No excuse.
Will solar panel manufacturers change their warranty?
A void 25-year panel warranty is a problem I don’t want to face in 10 years’ time. As the installer of the panel, the buck stops with me if your warranty is void due to an install error. So, as you might expect, I got my freedom fighter hat on. I contacted the two panels that we recommend and install: SunPower and Qcells.
SunPower solar panels
I rate Sunpower primarily because of its Maxeon cell technology. It’s tangibly different and better than any other solar cell.
A few years ago I visited SunPower’s Headquaters in Califorina and manufacturing facility in Mexico. It’s a tight ship – a far superior facility than the Chinese solar panel factories that I’ve visited.
QCells are easily the solar industry leader in research and development. Others are just trying to keep up. Look up the recent QCells successful patent enforcement. More importantly, QCells are the first in the industry to pass the most rigorous TUV Rheinland quality-controlled PV testing. Check out the CEC list for that. And finally, out of all the solar panel factories I’ve visited or heard about, QCells Korean factory is the clear winner for quality control and automation.
Holding SunPower and QCells to account
But that doesn’t stop me from having a crack at SunPower and QCells over their get out of jail free cards. Just because every other panel manufacturer gets away with it, QCells and SunPower should be held to a higher standard. So I contacted both SunPower and QCells to update their installation manuals to reflect reality.
SunPower were more open to giving me a statement, but that makes sense with SunPower’s Maxeon cell. SunPower Maxeon cells have a copper backing that is uniquely designed to handle hot spots. And the SunPower Maxeon cell has a lower reverse module voltage, so the bypass diodes don’t need to operate as often.
It took four months of back and forth, but I finally got clarification from SunPower. In essence, they say we can install SunPower panels in shade as long as it wasn’t permanent shade. We’ll get to the details of that soon.
QCells, on the other hand, were much more reluctant. “Mark” they insisted “Panels aren’t designed to go in the shade”. Then they gave me a letter explaining the different risk levels of installing panels in the shade. The more shade, the higher the risk of voiding the warranty.
Now, to be fair, talking with both the SunPower and QCells engineers made me realise this wasn’t a small problem. These clauses were in the installation manuals for a good reason. There is no doubt that some shade situations will damage a solar panel.
But was QCells going to allow us to install panels in partial shade? I don’t care how good the R&D team are, and no matter how good their manufacturing process is, I can’t sell a panel where the warranty might be void just because of occasional shading. And for a while, it looked like QCells were not going to give us much leeway. But after much back and forth, I got the answer I was looking for.
QCells finally gave me a letter stating that we can install their panels in shaded situations, but just not in constant shade. I’m not going to share those statements publicly, SunPower and QCells have said they will update their install manuals in due course.
A clarification on shade
But my summary of what their statements mean is:
Don’t install your solar panels in a location where they will see partial shade ALL DAY long. For example: directly behind a whirlybird or TV antenna.
(By the way, this would be a classic failure of your $4000 super special bill buster installation.)
Don’t install your solar behind a parapet wall, permanent edge protection, or an aircon unit.
(This would be a fairly common mistake on cheap and nasty commercial installations.)
Do microinverters help protect your panel?
Just as a side note, neither QCells or SunPower have made any requirements to use microinverters or optimisers. However, if you install Enphase microinverters on the panels that are installed in significant and prolonged shade, in my understanding, you’ll greatly reduce the chance of that panel failing. To their credit, LG is the only panel manufacturer I know of who mention the benefits of microinverters in prolonged shade.
The rest of the solar panel industry needs to follow suit
Now that SunPower and QCells have lead the way, it’s over to the other panel manufacturers. It’s time to come clean. If you don’t want to take the risk of allowing your panels to be installed in the shade, let everyone know that. Then nobody will install your panels because, you know, trees grow and chimneys get swept by people that don’t read solar panel installation manuals. But if you actually want people to buy your solar panels, then fix up your installation manual. Hand in your ridiculous get out of jail free cards attached to your 25-year warranty.
The 25 year “performance” warranty on a cheap Chinese Solar panel, or any panel for that matter, is a whole other topic. Who gives a warranty that will last till the year 2046?
Almost all panel manufacturers have a get out of jail free clause written into the warranty. They effectively say, don’t install your panels in any shade – ever. There is a reason behind this, because significant shade can damage even quality solar panels. But the clauses in most installation manuals are totally unrealistic and not suitable for real-world conditions. SunPower and QCells have now come to the party. Keep your eye out for their updated installation manuals. Now it’s over to the other panel manufacturers. If they don’t come to the party, I’d strongly advise against supporting their product.
Mark Cavanagh is the owner and manager of MC Solar & Electrical. He is an electrician, accredited solar installer/designer and an electrical contractor.