Improve handling of sub-hourly timesteps for front of meter stand alone battery

[brtietz]

Describe the bug
The stand alone battery models should work for sub-hourly runs (and do, behind the meter) but the front of meter models don't have a well defined key for what determines the timestep. Setting up 15 minute PPA and dispatch data throws an error.

To Reproduce
Steps to reproduce the behavior:

1. Set up a front of meter stand alone battery case
2. Set the PPA time series to 15 minutes
3. Set manual dispatch to 15 minutes
4. Run the simulation
5. See error

Attached SAM file is configured to reproduce the error:
standalone_battery_timestep_error.zip

Expected behavior
Stand alone battery should run with sub-hourly data in all configurations.

Screenshots

Desktop (please complete the following information):

• Version 2022.11.21, 2012.12.02

Note that it is easy to work around this issue in PySAM/the SDK, since the length of gen can be specified by the user. The workaround in the GUI is to specify a 15-minute weather file in a PV-Battery case, and then set the DC losses to 100%.

[cpaulgilman]

See also this discussion on SAM forum: https://sam.nrel.gov/forum/forum-general/4307

[brtietz]

Digging into the SSC code a bit, the front of meter models key off of the number of steps under "grid curtailment." It sounds like we should be able to fix this in lk.

[brtietz]

The behavior of the PPA/merchant plant models is inconsistent for PV+Battery cases, so it's hard to determine whether this should be fixed in lk or ssc. For example: pv+battery merchant plant gracefully handles a 15 minute time series with hourly gen, but single owner throws an error. Determine whether the PPA models should be more flexible, and if not what the scope of any lk fix should be.

Punting to the patch since this is patchable.