Several expressions can be used to find SAZM. In the present case. in the present case, eq 5.16 is used.
In Summer the Solar azimuth changes from northeast to northwest through east, South and
West. If the solar azimuth is taken beginning at the south, it decreases from over 99 degrees
to zero and then increases to over 90 degrees. Although the expression with COS can give
these angles correctly, that with SIN gives only the angle between 0 and 90 degrees because
it is restricted by ASIN.
In the present program, calculation of azimuth is not included, because it is not
necessary. If it is included, some consideration should be given to computer error, because
the time step in these calculations is small. If the calculation begins at exact solar noon --
that is, azimuth 0 -- ACOS(0) should be 1, but it can be a little bit larger than 1. An error
message told us this had happened in our early calculation. The discrepancy is solved by
filtering, such as we have in the program in Fig. 6.3. In the section on "* Calculation of
solar radiation", we have an IF statement that holds ALTS at not less than 0.1. If you look
at the remaining several statements, it is not difficult to understand why it is necessary to
have this filter. The value of PP is less than 1; therefore it is meaningless to calculate PPP
with a large. value of ALTC.