AC/DC Ratio in SAM API

Hey SAM community,

I’ve been developing a script that integrates Google Sheets with SAM to streamline the process of entering project details into SAM, displaying outputs, and performing calculations based on these outputs. However, I have a question about the calculations created from the API versus the desktop application.

Currently, my Google Sheets program uses the AC size of the microinverters to calculate the system capacity and doesn’t account for the DC size of the panels. However, in the SAM desktop application, I use the DC rating of the panels and the AC/DC ratio based on the relative size of the microinverters. This seems to be a significant factor in accurate modeling, but the SAM API lacks this consideration, and I’m concerned that my estimates might be inaccurate without addressing this point.

The function is designed to:

1. Retrieve project parameters from Google Sheets.
2. Calculate system capacity based on microinverter output and quantity.
3. Make an API call to PVWatts to get estimated monthly energy production.
4. Adjust these estimates for shading.
5. Calculate the total annual energy production.
6. Update the spreadsheet with the calculated annual production.

I would greatly appreciate any suggestions on the impact this discrepancy has in estimating production, or any feedback on improving my current approach.Thanks for your help!

Hello,

Documentation for the PVWatts V8 API on the NREL Developer Network is here: developer.nrel.gov/docs/solar/pvwatts/v8/ .

This API uses the same inputs as the PVWatts implementation in the SAM desktop application and the online PVWatts Calculator ( pvwatts.nrel.gov/ ).

The 'system_capacity' input parameter is the PV array capacity in DC kW. The 'dc_ac_ratio' input is the PV array capacity in DC kW divided by the total inverter AC capacity in AC kW.

Best regards,
Paul.