Max Inverter Current (Idcmax)

Paul,

The reference is below from the 2020 NEC, this was added in the 2017 NEC. Please note that not all inverters have a maximum DC input current, so it is not something listed in the CEC database. When inverters do not have a DC input current limit, they rely on the maximum power limit to regulate current. In both cases, the inverter increases its MPPT voltage to reduce power and current input, where the excess power is lost to recombination or dissipation in the cells. It is quite common for an inverter with multiple MPPTs to include this current limit. As Bifacial modules become more common, this current limit is necessary to keep DC conductors size reasonably, otherwise they must be sized based on the short circuit current of a bifacial module, when experiencing full bifacial gain on a low DC voltage peak cell temperature day, made worse when a frameless bifacial module is used. 

Thank you for this information.

Could you attach the image of the NEC reference as a file instead of pasting it into the forum editor? Pasting images does not work reliably.

Best regards,
Paul.

Thanks for reposting. Images do not render correctly unless you upload an image file as an attachment by clicking the Attachments button below the text editor and then insert the image into your post. I think only part of your image made it into the post.

Anyway, I found this link to a copy of that section of the NEC code here up.codes/s/circuit-sizing-and-current and attached a screenshot of the text as an image:



I am curious about the source of informational note that mentions SAM. It references the documentation of the Sandia Module model, but does not explain how to use the model for this purpose. The Sandia Module model is available in SAM by choosing the option at the top of the Module page, but it does not have an up-to-date library of modules.

If necessary, SAM does adjust the array voltage to prevent the array power from exceeding the inverter's power rating. SAM does not report the DC current, but you can calculate it by dividing the "Inverter DC input power" by the "Inverter MPPT 1 Nominal DC Voltage." SAM does report the "Subarray 1 short circuit DC current." You can find these variables by filtering the lists on the Data Tables or Time Series tabs of the Results page using the terms "voltage" and "current."

Best regards,
Paul.