Max Inverter Current (Idcmax)

The maximum current that an inverter will pull is listed on the inverter input page as Idcmax. In this case Idcmax of the inverter in question is 30A. Although this is included in the inverter input page (Idcmax), I do not think that SAM is checking it. When I export the hourly data for energy (Net dc array output (kWh)), which for an hourly series is equal to average power, and voltage (Inverter dc input voltage (V)), then calculate the amperage pulled by the inverter, the simulation in fact does go over the maximum amperage. Once I manually correct for the max amperage value of the inverter, the annual energy forecast drops by about 25%.

I believe that this client can rectify the issue by changing the layout of the strings to boost voltage, but my concern is that SAM runs the simulation in an amperage regime above the maximum of the inverter, then reports those energy figures as valid.

Thoughts?

Hello,

For now, SAM does not limit the operating currents or voltages in the system, so it is possible to model system configurations that in practice may exceed the inverter design limits. Keep in mind that SAM is a pre-feasibility model, not an engineering design tool. You can use SAM to get a good indication of what the system will cost to operate, and to make some early decisions about the project's financial structure, but it is not appropriate for making more detailed technical design decisions.

You can do some rough checks on the limits as you describe, but because, as you note, SAM runs hourly simulations, you have no information about voltage and current levels within each hour.

Best regards,
Paul.

Hi again,

I'd like to follow up on my reply to say that we are considering improving the inverter model so that it clips the hourly average current (Pdc/Vdc) to the inverter's rated Idcmax, and adjusts the inverter's power output accordingly. However, many of the inverters in the CEC/Sandia inverter database do not have values for Idcmax, so we also need to address that issue as part of the improvement.

Best regards,
Paul.

Hello Paul,

is this still being considered? The NEC section 690.8(1)(a)(1)(2) references specifically to SAM, however SAM does not have this functionality.

Thanks,

Hello,

Yes. This is still on our wish list: github.com/NREL/SAM/issues/272

Can you provide a link to the mention of SAM in the NEC documentation?

Best regards,
Paul.

Hello Paul,

See the below reference which was added in the 2017 code. Reference below is the 2020 code.