pv system connected to sub-panel

[Jest Waitn]

If you mount the string inverter near your main panel, you can run the 500 Vdc the long distance with less loss and just have a short AC run.

i don't want to do this. don't want long dcv runs.

[Jest Waitn]

The grid voltage is not constant so you will need to measure them at the same time or at least a few times close to the same time.

of course. and neither is the temperature constant.

[Jest Waitn]

If you mount the string inverter near your main panel, you can run the 500 Vdc the long distance with less loss and just have a short AC run.

so then, bar making a long dc power run, there is no real advantage in using the string inverter?

[SunEagle]

The grid voltage is not constant so you will need to measure them at the same time or at least a few times close to the same time.

I would also add in the fact that the grid voltage tends to go up at the end of the day or on weekends when commercial & manufacturing loads are turned off.

[ButchDeal]

I would also add in the fact that the grid voltage tends to go up at the end of the day or on weekends when commercial & manufacturing loads are turned off.

some areas are more stable than others but here is a typical example from one of our inverters in PA a little west of Philadelphia.
so just from the 25th to the 26th you have an average day time swing from 248V to 243V Chart.jpg

[SunEagle]

some areas are more stable than others but here is a typical example from one of our inverters in PA a little west of Philadelphia.
so just from the 25th to the 26th you have an average day time swing from 248V to 243V Chart.jpg

When I worked at an industrial facility we would see the 4160v main power voltage creep up on Friday afternoon as the weekend started and then suddenly drop as grid line capacitors were switched off. The opposite would happen on Monday morning when you would start to see a drop in voltage as the grid got loaded up and then a sudden jump in voltage again as capacitors were switched back on.

[Jest Waitn]

on this note, then how likely is it that the grid voltage here might hit 261vac and cause disruption to the inverters?

[Jest Waitn]

If you mount the string inverter near your main panel, you can run the 500 Vdc the long distance with less loss and just have a short AC run.

since virtual net metering is not supported by the POCO, an alternate possibility is to relocate the main power to the 'jump pole' about 75' closer to the transformer. the sub-panel can also be relocated and wire the PV array to it with about a 125' hop to the transformer from the PV array. but this would be a lot of work and possibly a greater hassle by having to bring the 'old stuff' up to most recent code. and i'd want to keep the old primary panel on the pole as a sub-panel for the well & house and to run the supply line overhead from pole to pole. don't know if this is allowed & it might cost a bunch of $.

[Jest Waitn]

so then, bar making a long dc power run, there is no real advantage in using the string inverter?

no one wants to commit to an answer on this?

[SunEagle]

no one wants to commit to an answer on this?

A string inverter usually costs less then micro's as well as reducing the failure point to one instead of one for each panel.

[bcroe]

no one wants to commit to an answer on this?

There are plenty of advantages to high voltage strings; some may not apply to your situation. Assuming you
have no compelling need for micros, the cost will be less in inverters and wire. There are fewer parts to fail,
and generally there will be a little bit higher efficiency. A lot of things can be done with panels to better match
up to your inverter plant and your weather, even after the initial build. See my thread Sun Hours for more
on that. Bruce Roe

[ButchDeal]

no one wants to commit to an answer on this?

string inverters are cheaper, single point of failure (instead of many), more efficient, more reliable.

Further there are other options as well, like SolarEdge optimized system which is kind of a mixing of micros and string inverter.
This is my preference as it is most reliable, low cost, meets all safety requirements easily, easy to monitor, and most efficient.

[J.P.M.]

no one wants to commit to an answer on this?

I'll add to the chorus: More reliable, less up front cost. Individual panel monitoring novelty usually wears off quickly. What more do you want ?

[ButchDeal]

Individual panel monitoring novelty usually wears off quickly.

I will just speak to this one. I personally disagree with J.P.M. on this one detail. though I agree looking at individual module data gets old. You set up alerts such that individual module data issues trip an alert. We have this and we monitor all our installs. We have been told that we have had the most module replacements by far over any other company, and all of them warranty issues. This is because of the module level monitoring. That said it is a small percentage but I have to imagine that since we are the only ones monitoring actively like this and we have the highest number of modules warranty replacements that other installers and even the big guys like SolarCity, SunEd, etc would benefit from monitoring at the module level.
SunEd specifically only monitors at the system level even though they install SolarEdge and Enphase systems, and I have been told that SolarCity does similarly.

JPM and others have pointed out that to a homeowner that monitors system level closely, a bad or partially failed module would often show up. Possibly but harder to automate an alert on that.

[J.P.M.]

I will just speak to this one. I personally disagree with J.P.M. on this one detail. though I agree looking at individual module data gets old. You set up alerts such that individual module data issues trip an alert. We have this and we monitor all our installs. We have been told that we have had the most module replacements by far over any other company, and all of them warranty issues. This is because of the module level monitoring. That said it is a small percentage but I have to imagine that since we are the only ones monitoring actively like this and we have the highest number of modules warranty replacements that other installers and even the big guys like SolarCity, SunEd, etc would benefit from monitoring at the module level.
SunEd specifically only monitors at the system level even though they install SolarEdge and Enphase systems, and I have been told that SolarCity does similarly.

JPM and others have pointed out that to a homeowner that monitors system level closely, a bad or partially failed module would often show up. Possibly but harder to automate an alert on that.

I appreciate and respect the difference of opinion.

But - there's always a but I suppose - you post raises some questions in my mind:

1.) If you've been told that you have "the most module replacements by far...", how would you answer those who suggest (and accepting for the time being the idea that all such modules are ostensibly created approx. equal) that rather than blaming the product, the higher replacement rate is due to the quality of the install ? Seems by your own admission, you have more replacements. Are your modules of inferior quality to those from the same source, or inferior to those used by other vendors ?

2.) How "small" (a failure/service call rate) as compared to string inverters ? Small seems a relative thing.

3.) If the modules are indeed created about equal, which seems at least plausible, and your failure rate is indeed due to better monitoring, could that mean the other such modules may be failing at something like an approx. equal but unreported or unknown rate? If so, that would seem to give at least some credence to my opinion and conjecture that small(er) failures of, say, one panel, would have a higher probability of going unnoticed by users. If so, why would I or any potential customer want to use a product or rely on a vendor who would sell such a product that might fail at a higher rate per install than a string inverter (if for no other reason than their being more of them per install), and have such failures slip under the radar, or, as an alternative, require a customer to perhaps be more diligent in their own monitoring. Seems to me a string inverter failure, being something like an order of magnitude larger and thus more prominent and more quickly noticeable, might be easier for an owner to catch rather than waiting/hoping/relying on monitoring from some company not as diligent as yours.

See my further posts for acknowledgement and correction of an error in referring to micro inverters or SolarEdge roof equipment as "modules". Patch : Replace the word "module" with the words "micro inverter or optimizer".