The Solar City Walmart Solar Disaster

[Lakewood90712]

So Wally mart has disconnected all it's store solar systems procured from Solar City between 2012 and 2018, and had filed suit, due to 7 fires and associated collateral losses. IIRC these are the roof of the store systems. I have seen several carport solar type systems at Sam's clubs. Those are much more costly to install, but no risk to the store from electrical fires.

Is Walmart giving up on solar PV, or just taking a time out and going with another vendor ?

 

[travelover]

Dunno, but I'd love to see those massive big box parking lots covered with solar panel roofs. Think how much cooler cars would stay while parked and the store could blast their AC for free.

 

[NW-Bound]

Dunno, but I'd love to see those massive big box parking lots covered with solar panel roofs. Think how much cooler cars would stay while parked and the store could blast their AC for free.

Only if the system does not set the store roof on fire.

I just posted about this story on another thread.

 

[travelover]

Only if the system does not set the store roof on fire.

I just posted about this story on another thread.

Yea, a pity but I think it had more to do with poor design or workmanship than solar per se.

 

[NW-Bound]

Yea, a pity but I think it had more to do with poor design or workmanship than solar per se.

Of course when you don't do it right, it hurts.

See: http://www.early-retirement.org/for...can-be-100-renewable-95073-5.html#post2287214

 

[NW-Bound]

Amazon said Solar City panels caught fire on the roof of one of its warehouses. Tesla said it was an isolated event at one of 11 Amazon sites with solar panels. Amazon said it would not install any more Tesla solar panels. Tesla said the connectors by Amphenol were faulty. Amphenol said it had no reason to think its connectors were the cause of any fire.

See: https://www.forbes.com/sites/rachel...ced-tesla-solar-panel-roof-fire/#2bca3ccf72c2.

 

[Just_Steve]

Amazon said Solar City panels caught fire on the roof of one of its warehouses. Tesla said it was an isolated event at one of 11 Amazon sites with solar panels. Amazon said it would not install any more Tesla solar panels. Tesla said the connectors by Amphenol were faulty. Amphenol said it had no reason to think its connectors were the cause of any fire.

See: https://www.forbes.com/sites/rachel...ced-tesla-solar-panel-roof-fire/#2bca3ccf72c2.

Tesla in business 16 years Amphenol in business 87 years, who are you going to put your money on?

 

[NW-Bound]

I dunno about this solar connector failure thinggy. Anything is possible, I guess.

I used a few MC4 connectors myself, but I bought by Internet order from China and the manufacturer is unknown.

Full disclosure: I own no Tesla shares or products, but Amphenol is a long-term stock holding of mine.

 

[Just_Steve]

Tesla in business 16 years Amphenol in business 87 years, who are you going to put your money on?

I dunno about this solar connector failure thinggy. Anything is possible, I guess.

I used a few MC4 connectors myself, but I bought by Internet order from China and the manufacturer is unknown.

Full disclosure: I own no Tesla shares or products, but Amphenol is a long-term stock holding of mine.

Guess that answered my question.

 

[NW-Bound]

Any connector can fail. Or it could be a bad solder joint inside a panel. A break in a high-voltage DC circuit will cause arcing, followed by a fire. I have previously linked in videos showing how normal AC circuit breakers cannot interrupt a DC current in a high-voltage DC circuit. And high voltage here is just 200V!

If a single-point failure can cause a catastrophic fire, then the design is not good.

Many inverters and solar charge controllers have a built-in arc-fault detection circuit, which allows them to detect an intermittent current to initiate a safe shutdown. It appears SolarCity equipment does not have this capability, or that the detector does not function correctly.



Here's how you can draw a long arc with just 4 panels in series.

Here's how an internal break in a solar panel will lead to a fire.

Here's how a regular AC breaker will fail due to arcing in a DC circuit. Warning to DIY'ers: you need the right type of DC breakers.

 

[ncbill]

Best for DIYers to stick with 48VDC & lower.

 

[JoeWras]

But Edison said DC was safer! He proved it by killing an elephant with AC. ... Or at least that's how the story goes.

 

[NW-Bound]

Best for DIYers to stick with 48VDC & lower.

That's the voltage of the storage battery. And I have not seen inverters that can take an input voltage higher than 48V nominal anyway. This means you cannot have a battery voltage higher than 48V, unless you build your own inverter.

Solar panel voltage is higher. And it has to be higher than the voltage of the battery in order to charge the latter. The charge controller is a DC-DC converter that steps down the voltage from the panels wired in series, in order to match the voltage of the battery.

Charge controllers typically accept panel voltages in the range of 100V to 200V. Some controllers for DIY'ers accept up to 600V. And 600V is typically the max voltage rating for the wire insulation, although some wires are rated up to 1000V.

If you want a lower panel voltage which is still higher than your battery voltage, it would really limit your choice of panels. Not counting small solar panels meant for mobile applications such as RV, large panels come in either 60, 72, or 96 cells.

Even the 96-cell panels do not have an output voltage high enough to charge a 48V battery on a hot day. This is because PV voltage output drops with rising temperature. There are 128-cell panels, but these rare and large panels are meant for commercial installations and not easy to get, nor installed.

And if you do not want to wire panels in series, then each panel must be wired separately to the charge controller which is situated next to the battery. For an array of, say 20 panels, that's a bundle of 40 wires of fairly large gauge.

If you want to wire the panels in parallel to reduce the number of wires, you have to figure out how many panels you can put on a large gauge wire such as 0 AWG, so that you will need to run multiple wires like that as necessary. And this depends on the distance from the panels to the battery and electronics. You will still need multiple large 0-AWG cables running from your panels to the electronics, but fewer than if you use the standard 10-AWG solar cables.

Even after going through calculations, it is best to try wiring some panels up with the length of wire that you will use, and do it on a hot day to see if it is going to work. Voltage drop due to the large amperage is often higher than calculated values, and I suspect that it is due to the quality of the copper. Use expensive oxygen-free copper wires? Yes, it will work better. It's only money.

 

[travelover]

But Edison said DC was safer! He proved it by killing an elephant with AC. ... Or at least that's how the story goes.

Worse than that they filmed the spectacle and it is on YouTube. Yech.

 

[NW-Bound]

Yes, the infamous electrocution of Topsy was filmed in 1903, and it is now on Youtube. Topsy was decreed a rogue circus elephant and was condemned by the owners to death either by hanging, strangulation, or poison. And they were going to make a spectacle out of it, and charge admission.

They ended up feeding Topsy with carrots laced with cyanide, prior to the application of 6,600VAC to the feet. The elephant was seen to topple over, and died quickly.

When electrocution was used for human execution, it sometimes did not work out as well, even with 2500VAC. Repeated zaps were needed until the condemned was declared dead.

The most notorious case was when the execution was botched due to a miswiring, and the surviving condemned was sent back to his prison cell for six months. When his lawyer failed to make the plea in front of the US Supreme Court to have the sentence changed to lifetime imprisonment, the condemned was returned to the electric chair, which worked properly this time after being repaired.

 

[JoeWras]

Sorry, I didn't mean to get us too sidetracked.

It is interesting to me that the DC power can pack such a punch when things go wrong. I used to take the "L" in Chicago, and would occasionally see some pretty impressive DC arcing. These were very transient as they usually involved the moving shoe running over some obstruction or losing temporary contact.

 

[Lakewood90712]

DC arc fires ? Fuses are your friend.

 

[NW-Bound]

The problem here is that solar panels are current limited. You can short the panel output, and the current is only so high, and in fact just a few percent higher than its operating current. In fact, the short-circuit current is one of the specifications of a solar panel, and is used for panel testing.

You would never short-circuit a battery because the current would easily go to more than 10,000 amps, but solar panels are routinely shorted to measure their current capability.

Hence, fuses are of limited use in a solar panel circuit. On the other hand, circuit breakers are not expected to trip either but they are used as switches to disconnect the feed from solar panels for testing or turning things off. Regular wall switches for AC current will burn up by arcing when used in a DC circuit.

--> A high-voltage DC circuit can cause an arc that jumps several inches, and can bridge over a blown fuse too. <---

PS. Below is a typical solar panel specification showing that the normal operating current is 5.20 amps, and the short-circuit current is merely 5.62 amps.

 

[NW-Bound]

Even if a fuse is blown in a DC circuit, a high-voltage DC circuit can cause an arc that jumps several inches, and can bridge over a blown fuse too.

Here's a video showing a DC current jumping across a knife switch with more than 1 inch of gap. The current is actually less than when the switch is closed and the load is operated. No fuse or breaker would trip in this case anyway.

Regular wall switches do not have a contact gap as long as the above knife switch. A failure is inevitable.

 

[NW-Bound]

Walmart's lawsuit alleges that even after the solar systems in all Walmart stores had been turned off in May 2018 as Walmart requested and Tesla agreed to, a fire still broke out at the Yuba City store in Nov 2018.

How could this happen with an inactive system, one may ask?

This can happen if the strings of panels are disconnected from the inverters, but the panels are still connected together in series. As a string, the panels still produce a high DC voltage, and can cause arcing to the grounded mounting frame. Indeed, Walmart produced some photos alleging that poor wiring practice caused the cables to be abraded by chafing against the metal mounting structure, leading to eventual failure of the cable insulation.

To disable a solar array, one must disconnect each solar panel from the strings. The hazard of solar panels may not be understood by laymen. Info from this lawsuit should be heeded by people working with the hardware, particularly DIY'ers who may have a cavalier attitude about solar panels.

For more info, the lawsuit filed by Walmart with many included photos can be downloaded here:

https://www.plainsite.org/dockets/download.html?id=283711125&z=a5c267e5.