Time Conventions in SAM

Sorry if you've already provided these answers elsewhere. If so, please feel free to simply point me to that source of help information.

I'd like to confirm both the 5-min. & 1-hr. interval data's time conventions of 1.) imported NSRDB weather data, 2.) SAM's geometrical sun angle calculations, and 3.) exported output CSV data.

For each of the above #1-3: What are the time conventions (i.e., what does a given timestamp represent)?
A.) Beginning-of-interval (left-labeled),
B.) Middle-of-interval (center-labeled),
C.) End-of-interval (right-labeled),
D.) Exact timestamp-calculated; often, middle-of-interval timestamp-calculated (center-calculated), or
E.) Mixed (e.g., some variables left-labeled & others center-calculated)

More detailed descriptions of the above options:

A.) Beginning-of-interval (left-labeled):
1990-01-01 00:01:00 timestamp represents:
A1- 1990-01-01 00:01:00 – 1990-01-01 00:02:00 (1-hr data)
A2- 1990-01-01 00:01:00 – 1990-01-01 00:01:05 (5-min. data)

B.) Middle-of-interval (center-labeled):
1990-01-01 00:01:00 timestamp represents:
B1- 1990-01-01 00:00:30 – 1990-01-01 00:01:30 (1-hr data)
B2- 1990-01-01 00:00:58 (?) – 1990-01-01 00:01:03 (?) (5-min. data)

C.) End-of-interval (right-labeled):
1990-01-01 00:01:00 timestamp represents:
C1- 1990-01-01 00:00:00 – 1990-01-01 00:01:00 (1-hr data)
C2- 1990-01-01 00:00:55 – 1990-01-01 00:01:00 (5-min. data)

D.) Exact timestamp-calculated; often, middle-of-interval timestamp-calculated (center-calc'd)
1990-01-01 00:01:00 timestamp represents:
D1- Exactly at 1990-01-01 00:00:30 (1-hr data), or
D2- Exactly at 1990-01-01 00:01:00 (1-hr data), or
D3- Exactly at 1990-01-01 00:01:30 (1-hr data)
D4- Exactly at 1990-01-01 00:00:58 (?) (5-min. data), or
D5- Exactly at 1990-01-01 00:01:00 (5-min. data), or
D6- Exactly at 1990-01-01 00:01:03 (?) (5-min. data)

Or, E.) Some combination (mixture) of the above, e.g., where certain variables (not involving sun position calcs) are left-labeled (#A1 for 1-hr data, #A2 for 5-min. data) and others (involving sun position calcs) are exact timestamp-calculated (#D3 for 1-hr data, #D5 for 5-min. data).

I believe the SAM Help Menu says the imported & exported (output CSV) data (e.g., weather data) time convention is beginning-of-interval (left-labeled) (#A). However, do all the (calculated & exported) sun position-dependent variables represent "middle-of-interval timestamp-calculated" (#D)? e.g., For timestamp 1990-01-01 00:01:00, are POA irradiance & other sun position-dependent variables determined at exactly 1990-01-01 00:01:30 (#D3) for the hourly case, whereas other variables not involving geometrical sun position calculations (e.g., GHI, Tamb, Wspd) represent summed or averaged values & are reported as "beginning-of-interval" (#A1 for hourly)? What about for 5-min. data?

For 5-min. interval data, I think I read that, for timestamp 1990-01-01 00:01:00, sun position-dependent variables represent data calculated & reported at the exact (not necessarily middle, in this case, but perhaps an instantaneous "snapshot"?), recorded timestamp 1990-01-01 00:01:00 (#D5); whereas, other variables not involving sun position calcs represent summed or averaged values over 1990-01-01 00:01:00 to 1990-01-01 00:01:05 and are reported as beginning-of-interval (#A2). Would you please confirm if this is correct?

Many thanks.

Hello,

I think the answers to your questions about the weather file convention and the convention used in calculations during the simulation are in Help here: samrepo.nrelcloud.org/help/weather_time_convention.htm .

For the dates that appear on the Data Tables tab of the Results page, for hourly data, the minute column is arbitrarily set to 0 (as in Jan 1, 12:00 am) even when the weather file minute column is 30. For subhourly data, the minute column on the Data Tables tab should be consistent with the minute values in the weather file, but it's worth checking to be sure. The time stamps in the Data Tables tab are generated by the data viewer from the simulation results -- they are not generated from the weather file. This is a known issue that we hope to fix soon: github.com/NREL/SAM/issues/437 .

Sorry this is a bit confusing, please let me know if I missed anything.

Best regards,
Paul.