Sam no long accepting sub hourly load files when hourly weather files used.

Dear Mark,

There are a couple of reasons we made this change. The main reason is that with the new battery model (for photovoltaic systems), it does not make sense to run simulations with hourly weather data and subhourly load data because the battery needs to respond to both power available from the array and required by the battery in the same time step.

Also, in older versions of SAM, when you used hourly weather data with subhourly load data, SAM used the subhourly load data to determine the peak load in a month, but the hourly solar data to determine the photovoltaic system's output in each time step. That did not represent how system might reduce the peak load very well.

So, in the current version, we think you should use the same time step for the weather data and load data. If you want to use hourly weather data with subhourly load data, you could modify the weather file, perhaps by using linear interpolation to estimate subhourly values from the hourly values.

Best regards,
Paul.

SAM's solar performance models will run with a weather file with time steps ranging from 1 minute to 60 minutes.

Best regards,
Paul.