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diy solar

Stand Alone Solar Arc-fault protection devices.


Yellow journalism?

Solar panels typically have 0.05% failure rate. "Tesla" (Solar City) systems, 2.9% caught fire!

2.9% of systems / 0.05% of panels = 58x as high a rate.
If a Walmart rooftop system has just 58 panels (half what I have), those would be equal numbers.

Of course, it is "system fires" vs. "panel failures", hopefully vast majority of panel failures isn't a fire!
 
I have Midnite Classics and I've had my Arc Fault trip. It stops incoming PV. The idea is that it can detect a bad/loose connection in the PV wiring that is 'arcing' and stops allowing load (stops current flow) so the arc doesn't burn something up. Gives you a chance to find the issue/fix.
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Arc Fault has sensitivity settings and in my case I didn't have an arc but made it 1 level less sensitive.

Midnite Classic Ground Fault is a DC version of GFCI in AC - and I believe it shuts off output amps (and therefore input amps).

Have any way to stimulate it with signals? Key a radio near it? Use a loop of wire to power a brush-type appliance with one leg brought near PV wire to couple? Since you can set sensitivity to a hair trigger, you might be able to get an idea what it is sensitive/immune to.

Some arc fault systems are sensitive to radio signals they pick up. Layout of PV wires and panels could affect that. Others might be affected by power line noise coupled into them.

I've become an EMI guy, and recently bought a "bulk current injection" system for work. That uses a current transformer to inject 1 to 10 V AC, sweeps frequency and modulates amplitude. Used for EMI/EMC compliance, to ensure system is immune. But Arc-fault systems should ignore some signatures, trip on others.
 
2 questions:
1. Are you saying arc fault detection would have prevented the Walmart/SolarCity fires?

2. 116 panels?!
 
1) You would think. But even after they shut off systems on surviving store roofs, more caught fire. With zero MPPT current drawn from them.
Something about faulty or incorrect/incompatible MC connectors. But that doesn't compute.

2) Only counting the ones up right now. Actually, I think that's 138 up. I'm in the process of swapping around; upgrading, hope to deploy more.
Not sure what I'll use all the power for. Any ideas?
 
Have any way to stimulate it with signals? Key a radio near it? Use a loop of wire to power a brush-type appliance with one leg brought near PV wire to couple? Since you can set sensitivity to a hair trigger, you might be able to get an idea what it is sensitive/immune to.
I haven't fooled with it other than to make it less sensitive. One could probably make it trip by setting sensitivity really high.
 
1) You would think. But even after they shut off systems on surviving store roofs, more caught fire. With zero MPPT current drawn from them.
Something about faulty or incorrect/incompatible MC connectors. But that doesn't compute.
That's the first I have heard that they continued to catch fire after disconnecting/powering down.

I realize those were probably 1500 VDC systems, that will arc right through a partially melted, crappy MC4 connector.
I realize that the 150 VDC MPPT that I am looking at has significantly less risk due to the system voltage, but now I want arc fault.

2) Only counting the ones up right now. Actually, I think that's 138 up. I'm in the process of swapping around; upgrading, hope to deploy more.
Not sure what I'll use all the power for. Any ideas?
I hear it takes a lot of juice to get fusion going.
Or if your enjoying the emi, you could ruin everyone's radio and possibly cell reception for miles on every direction.
 
I hear it takes a lot of juice to get fusion going.
Matter of degree? When I 'tested' my 3s strings (120v @ 9a) as the guy was hooking them up on the roof, I caused arcing between + and - to show the guy (and to test it). Even at 9a you can induce a continuous / pretty strong arc - enough to melt wiring if it kept going.
 
That's the first I have heard that they continued to catch fire after disconnecting/powering down.


I hear it takes a lot of juice to get fusion going.

The tipping point:


I make 1.3 MJ every hundred seconds. Now I just need to improve efficiency of path between flashlamp charging and X-ray on capsule surface (or was that compression energy?) beyond the 1% NIF is running.

It can be done at a smaller scale (further from break-even). I've seen/made use of small ones:



Or if your enjoying the emi, you could ruin everyone's radio and possibly cell reception for miles on every direction.

Yeah, that's the ticket.

I did that as a kid, welding together a 3-axle van for some guy. During some kind of football game. The authorities came knocking.

Actually, I'm more interested in how to ruin their radio. And their cell phone. Magic Smoke from afar?
 
I knew about the Walmart Tesla stuff. I didn't realize how bad it was.

"But Walmart said another fire still occurred at a California store, even though the panels had been disconnected for several months. The company said that the wires on the store’s rooftop were still sparking when it discovered the fire."

So, definitely an arc fault!

"Walmart said it later found out that Tesla ignored an alert from that store’s solar panels, which Walmart said was the likely cause of the fire. In the court documents, Walmart said ignoring the alert reveals “Tesla’s utter incompetence or callousness, or both.”

That's rough, even for a lawyer.

Ha, I was thinking about NIF, almost posted a link.
 
I stumbled across this arc fault detector on ebay.
But, I can't find any specs to know if it is for DC or AC. Or even anything at all.

 
That link has a lot of good PV fire pictures.

They seem to be pushing "low voltage DC" very hard.
They said AFCI won't protect against arc to ground. I think it will if fault only a 1 place, no second path to ground available.
A fault + to - would keep burning. So situations can develop you can't stop.
As it said, micro inverters run on voltage of single panel, and optimizers can drop the voltage significantly.

Informative, but pushing for micro inverters.

Yup.


The commercial scale PV world uses high voltage strings of panels. You can get a 4 MW inverter from SMA, feed it a huge fused PV array.
Arc-fault can be a problem. WalMart had 7 fires from Solar City installations, and some went up even with operation of the system shut off.
I don't know how to make that failsafe except with electronics (or electro-mechanical) devices per panel, and I hate to add the complexity.
 
Something like that, module-level RSD.
Coupled with AFCI control to activate RSD.

These are usually switch-mode power supplies, take in PV panel voltage and perform either optimizing, or drop to a low (e.g. 1.0V) output in shutdown.
One issue is if their own playing MPPT and outputting a different power/voltage curve messes with the head of string level MPPT.
Another would be interference (that could be mistaken for arc-fault), which this one claims to avoid:

"STABLE
  • Eliminates Unwanted AFCI Nuisance Tripping
  • RSD-S-PLC Noise Spectrum Density is far away (isolated) from AFCI noise"
 
I’d like to go roof top. But I’m just not going to do it without tier 1 panel level shutdown capability and all fault detection.

My roof will handle about 30 panels; so it’s another roughly $1,000 for my off-grid cabin. Worth it.
 
I'm pretty frustrated by this ... even the "built in" AFCI in the inverters don't do enough ... here's a rather relevant article out of Australia (where they use "rooves" which made me chuckle): https://www.acsolarwarehouse.com/news/solar-fires-dc-arc-faults-on-solar-systems/
Wow ... this is a very good article.
Just read it - fantastic article. Clear and explains/shows the issue.

This is one of the reasons I soldered my wire -> MC4 connectors instead of just crimping. Hoping my Midnite Classic Arc Fault detection will cover one of the cases / better than nothing. :)
 
Just read it - fantastic article. Clear and explains/shows the issue. This is one of the reasons I soldered my wire -> MC4 connectors instead of just crimping. I have a cement tile roof and I'm hoping not to have to fool with panels up there for the rest of my life :)

Series arc-fault was already handled by AFCI.
If a rodent chews through your wires and you get a parallel fault, it will arc.
Only fix we've identified is to plug those MC connectors into module-level shutdown. But your fireproof roof is a plus.

Remember pay phones? They had a metal loom around the handset cable. that should be fairly rodent-proof. Flexible metallic conduit?

 
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