az = sin-1(sin(off)/cos(e))
em = tan-1(tan(off).tan(e)/(sin(az) + tan(off).cos(az)))
az = additional azimuth angle added by primary mirror
em = required elevation of the primary mirror
off = offset of the primary mirror from centre
e = calculated elevation of the sun
Now the required machine position can be calculated from the elevation and azimuth angles of the sun.