Due to the age of the original topic, along with several forum crashes over the years, I went back and recovered the XML script that was collaboratively developed back in 2003 for calculating the sun angle:

 

<String>
 %( (* zulutime+longitude/15 *)
 (P:ZULU TIME,hours) (A:PLANE LONGITUDE, degrees) 15 / +
 (* (7.3*sin((dayofyear-3)/365.25*360) *)
 (P:ZULU DAY OF YEAR,number) 3 - 365.25 / 2.0 pi * * sin 7.3 *
 (* -9.8*sin((dayofyear-80)/365.25*720)) *)
 (P:ZULU DAY OF YEAR,number) 80 - 365.25 / 4.0 pi * * sin -9.8 * + 60 / - (>L:local_sun_time,number)
 (* 23.5*sin((dayofyear-80)/365.25*360) *)
 (P:ZULU DAY OF YEAR,number) 80 - 365.25 / 2.0 pi * * sin  23.5 *
 (* (abs(lat)-90)*cos(localsuntime/24*360) *)
 (L:local_sun_time,number) 24.0 / 2.0 pi * * cos90
 (A:PLANE LATITUDE, degrees) abs - *(A:PLANE LATITUDE, degrees) 0 >
   if{ - }
   els{ + }
 (>L:local_sun_angle,number)(L:local_sun_angle,number))%!.4f!
</String>

Another version, with time

 

(P:ZULU TIME,hours) (A:PLANE LONGITUDE,degrees) 15 / +
(P:ZULU DAY OF YEAR,number) 3 - 365.25 / 2.0 pi * * sin 7.3 *
(P:ZULU DAY OF YEAR,number) 80 - 365.25 / 4.0 pi * * sin -9.8 * + 60 / -
(>L:local_sun_time,number)

(P:ZULU DAY OF YEAR,number) 80 - 365.25 / 2.0 pi * * sin 23.45 * dgrd
(>L:declin,number)
(L:declin,number) sin (A:PLANE LATITUDE,radians) sin *
(L:declin,number) cos (A:PLANE LATITUDE,radians) cos *
(L:local_sun_time,number) 12 - 24.0 / 2.0 pi * * cos * + asin rddg 1.0
(A:PLANE ALTITUDE,km) 6370 / 1 + / acos rddg + int
(>L:local_sun_angle,number)

Thanks, Jan. Someone at FS Developer was asking about this yesterday, and I remembered this discussion and collaborative effort from so many years ago. It's fortunate that most of the thread remains more-or-less intact after several forum crashes, not to mention forum software changes!