HDRi Sun.

[akinlolu olugboji]

 

which HDR are you using?

I would render from the TOP view, not from perspective.

Once shadows are distributed this evenly, let it cook a little moore to see, which ones will disappear first.

From the look of the image posted it seems the most of light (=sun) goes from SSW direction - which corresponds with the length of the shadow.

There is no need to calculate the sun direction accurately - just put it to SSW direction to the appropriate height, corresponding with the time of day and the season (from te HDR itself you can usually tell if it is winter, summer, morning, evening...)

All in all - no need to be too accurate.

 

More passes and top all shadows disappear. 

[Roy Hirshkowitz]

Use the Path Tracer, you'll get an answer quicker.  If you don't get a predominant direction then it won't matter where you locate the sun.

[akinlolu olugboji]

50 passes gave me this.

[Roy Hirshkowitz]

That's a pretty clear direction.  Now try to get a similar shape using the sun.  Use the Azimuth to get the direction right, and the Altitude to get the size of the shadow about right.

[Ros. Riha]

well, then it seems your HDRI is lit from SE direction, so be happy and give it a try...could you post a thumbnail of how HDRI looks like?

[akinlolu olugboji]

[akinlolu olugboji]

I believe I got it thanks.