This paper presents a life cycle assessment (LCA) of the solar heat injected in a District Heating Network (DHN) by a new solar thermal power plant in Geneva. An environmental Life Cycle Assessment (LCA) is conducted according to ISO 14040, ISO 14044 and SN EN 15804+A2:2019. The scope of the study includes the complete life cycle of the solar power plant heat generation system. The baseline GHG emissions results show that the solar heat injected is responsible of about 15 to 18 gCO2-eq per kWh depending on whether we account for the environmental impacts of the steel gratings or not. This value is mostly determined by the manufacturing and use stages. Different sensitivity analyses are then performed in order to test the robustness of the main influential parameters (e.g., lifetime, efficiency, electricity mix) and better quantify the variability of the GHG emissions. Finally, this LCA study of a solar thermal plant connected to a Swiss DHN provides a first value of the solar heat in comparison with other heat production routes for DHN already provided in LCA databases such as the Swiss KBOB 2009/1:2022 platform for LCA in the construction sector.