Thermochromic films of MgxV1-xO2 were made by reactive dc magnetron sputtering onto heated glass. The metal-insulator transition temperature decreased by similar to 3 K/at. %Mg, while the optical transmittance increased concomitantly. Specifically, the transmittance of visible light and of solar radiation was enhanced by similar to 10% when the Mg content was similar to 7 at. %. Our results point at the usefulness of these films for energy efficient fenestration