Hi again,
Seville is on 37.38 N, 5.98 W. Considering the equation 1.5.2 from "Solar Engineering of Thermal Processes" (by Duffie and Beckman) we will have:
1- Seville has 1 hour difference with GMT---> so: L_st = 15 * 1 = 15 degrees West
(on 21st of Dec we have n=355, so B= (n-1)360/365---> B = 349.17, therefore E = 2.17 min (equation 1.5.3))
Solar Time-Standard Time = 4 (L_st-L_loc) + E = 4 (15- 5.98) + 2.17 = 38.25 minutes
Hence on 21st of Dec at Solar Time = 12:00 we will have the local standard time equal to : 11:22
at this time: solar zenith angle should be minimum. But surprisingly, this is not we see in the curves. that is why it is confusing for me. In the Graph the minimum Zenith angle happens at 8509: means 14:00- How can you interpret this discrepancy?