In the present study, a novel solar-based building energy system, which is integrated with both electricity and district heating grids, is proposed and modeled. The solar system uses photovoltaic-thermal panels and has neither a battery nor a heat pump. The elimination of the battery and heat pump is proposed to reduce the cost of the system to motivate the building owners to adopt the solution as a cheaper energy system for their buildings. In this way, the building energy system would be able not only to produce a major portion of the heat and electricity demands of the households but also to supply its excess production to the grids to decrease the energy bill of the building. As district heating systems are on the verge of a transformation to their next generations, it is important to know how this system would respond to the future designs and standards of district heating systems. That is why the simulations are accomplished based on different district heating integration scenarios, i.e. existing, low-temperature, and ultralow-temperature district heating systems. For doing the simulations and comparative analysis on the performance of the system in various dynamic operating conditions, TRNSYS software is employed. The results show that the ultralow-temperature district heating model is the most suitable case for integration with the proposed system. In this case, the building energy systems will supply over 400 m3 hot water to the heat network and about 1940 kWh surplus electricity to the power grid over an entire year. Due to a lower panel temperature, the system produces the largest amounts of electricity and heat (3647.4 kWh and 9118.5 kWh) compared to the other two cases. The maximum overall efficiency values of 74.51%, 62.35%, and 52.35% for ultralow-, low-, and the 3rd generation-district heating models are achieved.