I am currently working on calculating the total irradiance falling on walls of different orientations (North,South,East,West) in Toronto. For this I have a weather data file that consists of DHI, DNI and GHI data. I prefer using the Perez model to calculate the total irradiance data on these walls. In my weather file that has hourly values of DHI, DNI and GHI during certain hours of the year both DHI and DNI are zero. Because of this my code generates a Division by Zero error…. How can I overcome this?