The performances of a 800 m2 solar thermal plant coupled to a large District Heating in Geneva has been monitored for more than one year. The solar field is composed of 400 high performance evacuated flat plate collectors manufactured by TVP Solar. It has an average operating temperature above 80°C. This plant has been equipped with sensors to monitor and follow its performances over time. In 2021, the solar plant has injected 536 MWh in the DHN which corresponds to a specific yearly productivity of 684 kWh/m2 /y or 45 % of average efficiency. Performances were compared between 2021 and the first half of 2022, with no observed performance degradation. The monitoring will be pursued at least until the end of 2024.