The ever growth of urban population has caused the increase of energy demand. This situation challenges the global public to find a way to produce energy in a secure, environmentally friendly, flexible, renewable and sustainable energy transformation system. One of the most promising technologies that can over-come most of the challenges is the district energy network. This paper focuses on best practice project in Latvia – fully renewable district heating system assisted by solar collector system with thermal storage tank and woodchip boilers. The article demonstrates solar impact to district heating system (DHS) in the framework of the current situation of DHS in Latvia by creating simulation in TRNSYS and validation with real system operation data. Real operational data show that the heat produced by solar collector system with thermal energy storage (TES) per year will cover up to 20% (10933,2 MWh) of the heating demand in under local climate conditions. The TRNSYS simulations concluded that the contribution of this type of solar system integrated into the DHS could be increased up to 50%, if the difference between consumption and heat produced by solar collectors were to be increased during the summer months, this could be achieved, for example, by increasing the solar collector field area