Since EST is aimed at obtaining diffraction-limited images, it must be located at a site where atmospheric turbulence above the telescope is minimized. With this in mind, there is unanimous agreement that the Canary Islands are among the best sites in the world for solar observations. The Observatorio del Roque de los Muchachos (ORM, on the island of La Palma) and the Observatorio del Teide (OT, on Tenerife) are the candidate sites to host the EST. For decades, they have demonstrated the excellence of the observatories to study the Sun, having obtained the best solar images ever recorded.
A site-testing campaign has been started within the framework of the Design Study to compare both sites. This campaign not only aims at obtaining information on the ground-layer turbulence but also up to several kilometers above the observatories. To that aim, several scintillometer arrays (two with a long baseline - 3.23 metres - and five with a shorter one - 0.42 metres) and one wide-field wavefront sensor (WFWFS) have been designed and constructed. The WFWFS has been installed at the SST, at the ORM, and operates simultaneously with regular observations. A second unit will be installed soon at the German VTT on Tenerife.