You don't want 50,000 columns of date and time as column headers in a table, no. That will NOT be conducive to using the data --
It's not at all clear why you have the small table of only seven elements at all here?
And, your code snippet above loads variables Tstc, Alpha_pmp, and T1, each of which are 50K by 1 vectors, but where's the required AirTemp variable of the same size--the P1, P2, P4 variables from the table that are defined aren't but the eight-long vectors from the short table. And, what is DNI?
The T1 variable turns out to be an (apparently) categorical vector of some model type it appears; we find that>> numel(unique(T1.PVModel)) = 20.
It looks as though these data could/would be ideal for a timetable of the 50K observations times with whichever of these other variables are wanted/need as the columns, one of which undoubtedly should be the above categorical of which model is which record.
One then could easily use varfun and grouping variables to operate over those records of each model as desired -- but trying to organize the other-way-round with the time values as the columns and column headers will not work well at all for 50,000 time records.