The paper is based on a research project, where the main objective was the development of compact and optimized solar and pellet system for apartment building. The solar and pellet system is very compact and enclosed in one standard size shipping container. This allows easy installation procedures. The system was designed and optimized with dynamic simulation using TRNSYS. The limited space available in the container called as well as for an optimization study for the calculation of the volumes to be allocated for the pellet storage and for solar buffer tank. The pilot project carried out has been continuously monitored: building thermodynamic parameters, solar collector and pellet boiler energy outputs and site-specific weather conditions were all measured. In this paper the results of the simulation study are compared with the preliminary data collected from the monitoring system. It includes important consideration for tuning solar pellet systems for multifamily buildings.