The European Union has set targets to increase the share of renewable energy in the coming years. Solar thermal energy is currently expanding and could possibly contribute to achieving the European targets. This paper evaluates the potentials of solar thermal energy from an energy system perspective along with the impacts of installing these potential for four European national energy systems; Germany, Austria, Italy and Denmark. The potentials are evaluated by applying energy system analysis of existing and future energy systems under different conditions such as substantial heat savings, expansion of district heating networks and with high-renewable electricity and heating sectors. The findings in this paper indicate that the national solar thermal potentials are in the range of 3–12% of the total heat supply and that installing the potentials will impact the energy system according to the energy system configurations. Solar thermal benefits reduce when moving towards a high-renewable energy system as other renewable energy sources start competing with solar thermal on energy prices and energy system flexibility. The findings can be applied to a diversity of energy systems also beyond the country cases of the study. The role of solar thermal should be to reduce the pressure on scarce renewable resources and to supply renewable energy in conditions where no alternatives are available.