Hi Rob,
Thanks for the clarification.
The SSC variable gen is the time series output of the system in kW. It is an array of length n_ts_sim, where
n_ts_sim = n_ts_hr * 8760 hours/year * n_yr_sim
and n_ts_sim is the number of time steps in the simulation, n_ts_hr is the number time steps per hour, and n_yr_sim is the number of years in the simulation. The number of time steps per hour is determined by the number of time steps in the weather file: For hourly data, n_ts_hr = 8,760 h/year, for subhourly data, n_ts_hr =time steps in weather file / 8760. (These variable names in italics are ones I made up for this description, not variables in SAM or SSC.)
The SSC variable system_use_lifetime_output is a boolean value (0 or 1) that indicates whether the gen array is for what we call a "lifetime simulation," meaning that the simulation time step spans more than one year. For most situations the weather file contains hourly data and system_use_lifetime_output = 0, so SAM runs an hourly simulation for one year, and the financial models like utilityrate5 and cashloan use a degradation rate to estimate system output (kW and kWh) in years later than Year 1, and an annual escalation rate to calculate costs ($) in years later than Year 0. If you set system_use_lifetime_output = 1, then SAM runs a simulation (using the same weather file) for each year in the analysis period.
Depending on the number of time steps in the weather file and how you define other inputs, the simulation may be hourly over one year, subhourly over one year, hourly over the analysis period (analysis_period in SSC), or subhourly over the analysis period.
Example 1: Hourly over one year
system_use_lifetime_output = 0
analysis_period = 25
time steps in weather file = 8,760
length of gen: n_ts_sim = 1 * 8,760 * 1 = 8,760
Example 2: Hourly over 25 years
system_use_lifetime_output = 1
analysis_period = 25
time steps in weather file = 8,760
length of gen: n_ts_sim = 1 * 8,760 * 25 = 219,760
Example 2: 15 minutes over one year
system_use_lifetime_output = 0
analysis_period = 25
time steps in weather file = 35,040
length of gen: n_ts_sim = 4 * 8,760 * 1 = 35,040
Example 3: 10 minutes over 30 years
system_use_lifetime_output = 1
analysis_period = 30
time steps in weather file = 52,560
length of gen: n_ts_sim = 6 * 8,760 * 30 = 1,576,800
Thanks,
Paul.