Running SAM (PVWatts) with GHI/DNI

Hi

I am wanting to run PVWatts with GHI/DNI data as opposed to the specified DHI/DNI pair. I obtain GHI/DNI data from ERA5 (it doesn't have any diffuse horizonal irradiance) and, at the moment, I use the irradproc module of the SSC library to compute the zenith and use this to compute DHI, and thereafter run. Is there another way to do this but in PVWatts itself?

Craig

Hi Craig,

PVWatts requires a weather file with direct normal irradiace, DNI, and diffuse horizontal irradiance, DHI.

SAM's Detailed Photovoltaic model accepts weather files with any combination of DNI, DHI, and global horizontal irradiance, GHI, and also accepts plane-of-array (POA) irradiance data.

You could either use the detailed model to run your simulations, or just use it to calculate the DHI values. If you are using SDKtool or another means to run the models using the SSC application programming interface (API), then you could run the pvsamv1 module to calculate DHI from DNI and GHI. The variable names for calculated irradiance components are:

df_calc = DHI calculated from DNI and GHI
dn_calc = DNI calculated from GHI and DHI
gh_calc = GHI calculated from DNI and DHI

For reference, the variable names for calculated plane-of-array (POA) irradiance, or irradiance incident on the surface of the array for each subarray is

subarray1_poa_nom
subarray2_poa_nom
subarray2_poa_nom
subarray2_poa_nom

Best regards,
Paul.