That is why i had VOC in quotes, that means i am using it in a non literal meaning, i.e there is some resistance connected to pull the voltage down.
VOC is a real property of solar panels. The wiring between them must be rated for the VOC to prevent a fault,
period. The
only way to get a VMP that goes all the way up to the wiring rating would be to have cutoff controls that are
within the listed solar module assembly. The code will
never allow anything else. Give up on that. (Yes, there are safety factors that mean this is overkill, but safety factors exist for a reason and the CMP will never change their minds on that.)
Yes it wouldnt actually be VOC in this case I understand that.
No, it could actually be VOC, in case of system failure. I think that's what you're not getting.
When the sun comes up the irrandiance will be lower too so I think the worst case that is often calculated for would be extraordinary rare.
The code needs to assure that installations
fail safely, not just that they operate safely. The rarity of failure doesn't change this one iota. This is true across the board, not just in PV systems.
I understand how it is done, just throwing around ideas here and that maybe a little more allowance could be considered. Let me give an example of how this might work and what got me thinking about it. I am off grid and I am putting another PV system at my house and the array will be 50% larger than the CC can handle. It is a 1400 foot wire run. The extra capacity is so I will have more output on cloudy days and so I can heat water. There will be some voltage controlled relays controlling water heating elements on the line side of the CC to extract the power that is beyond the CC capacity. Because of the long wire run, it is most efficient, cost effective, and I get the most bang for the buck to run the voltage as high as possible. Because of this I may want to run the VMP close to 550 for say 95% of the operating time even if it means using controls to disconnect and/or short out the array if the voltage exceeds 600 for that other 5% of the time. Anyway that what got me thinking about this and if perhaps something analogous could be applied to "normal" systems. Us off griders are on the cutting edge and way ahead of current codes and practices
This system design you've described makes little sense and would work badly. One does not run an array directly to multiple loads where one of them is a MPPT CC and the others are water heating elements. The latter will mess with the former and cause it to work suboptimally. More than one MPPT device on an array will not work either.
I believe the 2014 code would allow you to have up to a 1000VDC ground mounted array, as long you don't have more than 600VDC entering a single family home. (Disclaimer: haven't read the new code in all that much detail yet). In other words, perhaps you could have a relay cut power to the house if the temperature dropped so low that the VMP was over 600V. Now, this would mean losing power on the coldest days of the year, which seems ... dumb. But in the particular unusual case you have described above, it might be that code gives you the 50V of wiggle room you are asking for.
Generally, I feel that either
a) you are still not really getting how the technology and engineering really works, OR
b) you are trying to argue, without really saying so, that "the code should really allow us to ignore VOC because that is not the operating voltage." Regarding this, there isn't a chance in heaven that the Code Making Panel will ever agree.
Sorry I didnt know commenting on improvements to equipment and changes in the codes was off limits here :roll:
I think what ggunn was trying to tell you was about staying within reality, not current equipment and codes. :happyyes:
I think you should be happy that both myself and SolarPro have given you an answer that is code-compliant and already more or less exists: module level electronics. There's no technical reason that SolarEdge-style power optimizers couldn't be manufactured to operate at higher steady voltages than 350VDC. There's also probably no reason that such electronics couldn't be made to string voltage to 600V output, which could mean being off the actual max power point, but only on rare occasions.
Maybe you should contact SolarEdge and make the suggestion.