Questions on the TMY weather data

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phren
Questions on the TMY weather data

what does the "time" mean in the second column of the TMY.CSV file

hello everyone
i have a question on the TMY file: what does the "time" mean in the second column of the CSV file?see below.
Date (MM/DD/YYYY) Time (HH:MM)
01/01/1987 1:00

my project is a Tower Power CSP, with Storage about 8 hours, and solar multiple about 2.5,and using "SAM/CSP Tower TES Dispatch/Uniform Dispatch" in the thermal storage page.

i have found,if i creat the TMY file with the real local time(GMT8) "01/01/1987 1:00 " as the first row data ,i got a reasonable result(capacity factor 44.9% ),in this situation, the first row in the created TMY file contains the GHI,DNI data of the local time 1:00.
but if i creat the TMY file with the universal time(Greenwich time) "01/01/1987 1:00 " as the first row data,i got a wrong result (capacity factor only 5.1%,comparing with the above 44.9%),and in this situation, the first row in the created TMY file contains the GHI,DNI data of theuniversal time 1:00.

why does each of the above two results differs so much from each other?

so how can i creat a correct TMy file ,with my own local Weather data,in which the time (hour) means the universal time(Greenwich time)
thank you in advance.

Paul Gilman

Dear phren,

If you are creating your own TMY3 files, you should familiarize yourself with the TMY3 file format, which is described in the TMY3 User's Manual (PDF). Table 1-3 in the manual describes the Time field as follows: "Time of data record (local standard time)."

SAM does not use the time stamp data from the weather file. It assumes that the first row of each column of data contains a value for the hour ending at 1:00 am on January 1 (local time), regardless of the values in the Date and Time columns.

The reason your results are different using the wrong time stamp assumption is that SAM makes solar angle calculations based on the time of day, assuming the time convention I just described. If you assume that the first row of data is for the hour ending at 1 am in London (universal time) instead of local time, then the solar angles and solar resource data for a given hour will be mismatched, and the simulation results will be meaningless.

Best regards,
Paul.

phren

thank you!

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