It sounds like you have a great setup for your off-grid cabin in Idaho! As a solar panel installer, I would recommend that you ensure that the voltage of your solar panels is within the range recommended by the AC500 specifications. If the voltage is too high, it could potentially damage the AC500 or other components of your solar energy system.
Very bland comment with no specifics. You're an installer, maybe not a designer. If you presented the method for calculating voltage produced and determining if it is acceptable, that would be useful.
He may have given enough info to do a preliminary evaluation. You could have done that and told him if it was at risk, and explained how it might work for a while, why it could fail later.
Regarding the Renogy and SanTan panels, it's important to note that the voltage of solar panels can vary depending on factors such as temperature and shading. Therefore, it's always a good idea to monitor the voltage output of your panels and make any necessary adjustments to ensure that they are operating within safe parameters.
Correct on temperature. Now how about explaining how to analyze that, and ensure positive margin?
I disagree with the monitor and adjust part. Calculate in advance, not monitor and adjust. Then after assembling the array, measure voltage before connecting to equipment, and confirm it is as expected. Polarity too. An anomalous voltage could indicate wired incorrectly.
You also did not address his thought that being used the panels would produce lower voltage, giving some margin.
The panels might produce less current, but likely very close to full voltage. No additional margin.
Additionally, using used panels can be a bit of a gamble as you may not know their history or whether they have been properly maintained. However, if you have tested them and they are producing the expected output, then they should be fine to use in your system.
maintained
How do you "maintain" panels and what happens to them if you don't?
How do you suggest testing a panel and finding what output it (a single panel) produces?
One of those vendors, by the way (Santan) is very good about taking care of faulty or damaged panels. But due to shipping cost it is recommended to order a few spares up front.
Overall, it's great to see that you are taking a thoughtful approach to your <link "solar energy system"> and seeking advice when needed.
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