Required input data to PVWATTs conversion

Hello,

I downloaded solar irradiance data for 2012 from the NSRDB, including February 29, because 2012 was a leap year. Available solar irradiance data are with hourly or half-hourly resolution. I am aware that SAM has a built-in macro that can perform a simple linear interpolation to downscale irradiance to a lower granularity (in my case, preferably 15-min). However, I would like to use a more sophisticated method to obtain the required granularity. My question is - what exactly does SAM's PVWatts model need as input weather data to convert solar irradiance into the AC inverter powers? I found this information here on the forum - SAM's photovoltaic model requires data for two components of solar radiation (direct normal irradiance, diffuse horizontal irradiance). Are DNI and DHI the only data needed for PVWatts solar-irradiance-to-AC-powers conversion? In addition, do I have to exclude February 29, because SAM does not currently support the leap year simulation? Is there a workaround to that?

Thank you,
Mara

Hi Mara,

You can find a list of the weather data elements required by each of SAM's performance models, including PVWatts in SAM's Help system under "Weather Data, Weather Data Elements" in the table of contents.

In addition to the solar irradiance data, PVWatts also requires ambient temperature (dry-bulb) in degrees Celsius and wind speed data in meters per second.

SAM should ignore time steps for February 29, but to be sure, I would exclude it from your weather file.

If you are constructing your own weather files in the SAM CSV format, you can find the format description in Help under "Weather File Formats, SAM CSV Format for Solar." We have also posted that section of Help as a PDF on the SAM website at sam.nrel.gov/weather-data/weather-data-publications .

Best regards,
Paul.