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Before throwing $4100 at the issue, I'd first ask Solar edge if the distance and wire gauge would have an effect. Remember we're offering advice from the "internet cafe" and they have a margarita special tonight. 
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There is something else you can do....it will take some time and effort on your part. It appears that the voltage rise (drop in electricians terms) is increasing over time. This leads me to believe that you have high resistant connections in your system. And those connections are getting worse over time.
My suggestion is to inspect EVERY connection in the system, clean and apply silver conductive grease on every connection. Do not confuse this with dielectric grease which will have the opposite effect. You are only out your time and about $50 worth of silver grease.
Good luck.Comment
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I will ask Solar Edge support tomorrow about the effects of wire distance and guage. I will also clean all the contacts. Would Deoxit work? I use that on all my stereo contacts.
By the way, where do I find the margaritas?Comment
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Use this......
But use it sparingly on the connections, if it oozes it can create short circuit.Comment
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Something that has not been mentioned is that are their any new solar producers that have come on line in your neighborhood? Surely your POCO should have forewarned you of those additional systems if any.Comment
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I'm making a little headway, at least in my understanding. Solar Edge says that they expect a 3% voltage increase with power generation with a 200ft. run, such as I have. With grid voltage set at 250v, I should expect to see 257.5v. However, I routinely see 260v which is the inverter shutdown threshold. They also say that excessive voltage increases are due to wire size being too small. However, they confirm that the existing #6 wire is per spec and should be fine.
The power company volunteered to dial down the local regulator to 248v and Solar Edge said that they can bump the shutdown threshold up a couple of volts. The combination may preclude the majority of shutdowns. I will also have an electrician the PV array connections and apply the conductive grease, as recommended here. We'll see. Thanks for all the comments and advice. I will let you know what happens. It only took a full year to get to this point!Comment
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Triplex1.JPG I went through that problem 8 years ago. My existing wire loop
600 ft long was only running at 3/4 capacity. BUT the losses
exceeded 3%, 540W in this case. That loss did not make me
happy. I was building 9V in the loop at 60A, at the end of every
sunny day the wire was warm to the touch. That constant thermal
cycling would tend to work connections loose, I had re tighten
some for a couple years befor they stabilized.
One day the PoCo had a brief outage to do some work, and came
back with my 120/240V high line, higher than ever at 127/254V.
BESIDES the 9V bucked in my wires, the PoCo wires added a
bit more, and my inverter 264V voltage monitors tripped out. I
could not run.
My point, just because the wire is not overheating, does not mean
an acceptable design. EFFICIENCY and operating margain matter.
Eventually I buried a 270 ft run of direct burial aluminum TRIPLEX
to bring my losses to 23% of what they had been, read about that
in one of my threads. The wire only cost $650 delivered, but bigger
termination equipment was needed to deal with the aluminum. The
convenient 3 wire triplex had a smaller neutral, fine since it did not
carry inverter current and did not need over sizing.
In the shorter term I did manage to get the PoCo to lower their
voltage, but I was not about to lose forever energy while waiting
to see if/when that would happen. The inverter voltage monitors
were nominally set for 240 operation, but the same inverter could
operate on a 277VAC line if so programmed. The voltage monitors
do not set the voltage, the power company does. So raising the
line-to-line and line-to-neutral monitor trip points was a short term fix.
Bruce RoeComment
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Bruce - Thanks for relating your experience. If I understand correctly, what your experience shows is that the initial wire loop was inefficient - meaning higher resistance? The higher resistance lead to greater thermal loss, and probably further increases in resistance - all leading to increased voltage over the line tripping the monitor off. Do I have that right? In my case, the 200ft. #6 line may be spec but may also be causing a slight increase in line resistance that increases in a daily cycle as inverter current builds (and falls). If the grid voltage is a little too high and the trip point a little too low the net result is frequent inverter shutdown, especially during sunny afternoons. Sound plausible?
One thing further: the problem seems to have gotten worse over the 4-year life of the system Is that likely due to damage to the #6 line from thermal cycling?
Tom ReepmeyerComment
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Just an FYI I checked my Solar Edge spec sheets and it's design is 120/240 volts with an operating range of 216V-260V. With your utility delivering 250V you lose 10V of margin from the get-go. Them changing the transformer taps to lower your incoming voltage can only help.
As to your question about damage to the #6, the cable itself is fine it's the connections that can loosen over time with the load cycling.Comment
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As Mike 134 says, any permanent increase in losses is probably at the wire
connection points, not in the run of the wire.
If you do the arithmetic, you can get a pretty good estimate of your wire power
and voltage losses. Temperature is a secondary, temporary effect. Arithmetic
here was 4 gauge wire running through 2 buildings and a 200' trench, the 600'
loop at .00025 ohm per foot had a resistance of .150 ohm. My 60 A thru .15
ohm gave 9VAC drop, which was boosted on top of the line voltage. That got
my energy to the meter for credit. But there is some more wire out to the pole
transformer, so the total boost was a bit more than 9V, to trip V monitors.
My 60A at 9V cost me 540W, maybe 800KWh a year. And V trips. Bruce RoeComment
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Another consideration is just upgrading the breaker. They are thermo-magnetic devices, and rely on the internal resistance to heat up the breaker for the slow trip function. Electricians tend to size breakers assuming a 60C rating for wire and terminations, even though most circuits are good for 90C. A higher-amperage breaker will have a lower internal resistance, and therefore a lower voltage drop. Here in the GWN, the CEC says 90C rated #6 is good for 75 Amps with no more than 3 conductors in a raceway or cable.Comment
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Nerdralph - Actually, I did replace the breaker, although I didn't mention it here. The original installation used a 60 amp breaker and at the recommendation of the head electrician at the new installer, Michigan Solar Solutions, I replaced it with a 70amp breaker. Didn't help, unfortunately.
The head electrician thinks the problem is with the power company's connections coming into my house and wants them re-crimped. Solar Edge tech support agrees. The power company has inspected these connections with thermal imaging and found nothing unusual. As a consequence they don't want to send a bucket truck and crew to check the connections. Impass.
I asked Solar Edge tech support about the trip voltage threshold for shutdown and they actually refused to answer my questions! They just referred me to the inverter data sheet. As far as I can see from that, the inverter operating range tops out at 264v, but I can see that the inverter actually shuts down when voltage is anywhere between 258v and 262v. Tech support will only say that "the parameters are set correctly" or something similar. I have to say that Solar Edge has been unhelpful and very frustrating to work with.
Mike 134 - Your post prompted me to wonder why the power company would set the local regulator at anything other than 120/240 which I believe is the service they are obligated to provide. They are turning it down to 123/246 and I expect that will help, but 120/240 might solve the problem.Comment
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My local power company (ComED) in Illinois shoots for 120/240 however anything +/- 10% of those numbers is considered acceptable.
As to your voltage depends on where you're at in the line. They need to be sure the furthest customer gets 240 so if your close to the transformer you'll see more.Comment
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Mike, that's a very good point. Here in Indiana the voltage supplied to customers is regulated by the Public Service Commission. If your voltage is outside of required parameters, then you have a right to complain. It's been my experience the POCO's are very responsive to complaints to the PSC, well at least here in Indiana they are.Comment
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