The NREL site permits you to download solar position data for the period from the year -2000 to 6000. For those who want to work independently from the web the c-code (spa.c, spa.h) and  the code for a sample program (spa_header.c) can be downloaded here.
Here is the main window of SPA.exe for Widows written in Visual Basic 6. It calculates a variety of data related to the position of the sun.
The program is based  on the extremely accurate data presented by the
helped me with  the C - code
Clicking on the button
                     'Change
                     Location'
(at the upper left of the main window) opens the window at the right.
This one presents a database of 3378
locations to choose from.
Another window is opened when clicking on the 'More' button (near the right edge of the main window).
It gives the sun data for any particular spot on the globe at any time.
When you click the 'Auto' button the current data are displayed  (updated every second)
A SOLAR POSITION CALCULATOR
There are two additional windows to enhance the usefulness of my program:
Click here to add text.