An electro-optical solar compass, designed and developed at the Frascati Research Centre of the Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), has been tested for geomagnetic measurement at the Concordia Station polar observatory. This device, compact, not expensive, fast and very accurate, is able to measure the Sun direction and, consequently, the North Pole direction, within 1/100 of degree. It is extremely more accurate and reliable than a magnetic compass and its performance is comparable with that of the expensive modern GPS and gyroscopic systems, without the drawback of long measuring time and/or latitude-dependency. The ENEA compass provides the direction of the true (geographic) North and can be used to determine the exact orientation of solar concentrating power plants as well as to calibrate other compasses or for topographic surveying and, finally, for geomagnetic measurements. For this latter purpose, the ENEA compass has been used during the last Antarctic campaign, in December 2017, carried out by the italian `Istituto Nazionale di Geofisica e Vulcanologia' (INGV) and aimed at magnetic declination measurements. The results show that at a very high latitude the measurements done with the solar compass are much more reliable than those obtained with GPS sensors.