Total Irradiance Calculations

[Andy Lam]

Hello,

I am trying to calculate the irradiance using the .get_total_irradiance function from PVLib for the 5-minute interval and hourly intervals. Given that all of the variables (e.g. DHI, GHI, DNI, surface_tilt, solar_zenith, solar_azimuth, albedo, etc.) that are needed to calculate the total irradiance are the same, I am getting a different total irradiance values between the 5 minute and the hourly intervals at a given time. 

Here is an example below, at 1/17/2018 at 10:00.

Is there anything I need to do differently when calculating the total irradiance between the 5 minute intervals and the hourly intervals? 

[cwh...@sandia.gov]

pvlib does "moment in time" calculations, i.e., there is no time-averaging of inputs inside pvlib. So I would expect exactly the same irradiance at two equal time stamps, regardless of interval between time stamps, as long as the same external data are provided.

The relative humidity values in the highlighted rows are different. Those are from outside pvlib. I'd start there, it could be that small differences in input are propagating to different irradiance numbers.

Cliff