Without trying to make it too complicated, try this one. as taught by the RAF nav school.
Take the time using the 24 hour clock (whole hours), multiply it by 1.5, add a zero and that's the sun direction in degrees.
Example: 4pm is 16hrs = 24+0=240 degrees. You've got to interpolate the in between bits and remember about any local daylight saving time but it was accurate enough to tell me how lost I was on a 3000ft hill.