Transition to Zero Energy Buildings requires on-site energy generation from renewable energy sources in order to offset the energy usage for building operation. Solar thermal collectors and photovoltaic panels are the most common building integrated renewable technologies and are used in order to reduce CO2 emissions and dependence on imported energy. A combined use of the later, designed according to the building energy demand can potentially maximize the benefits of solar energy and enhance the environmental and financial building performance. SEMERGY is an innovative performance-based optimization environment for building design and currently lacks of a tool for modeling of photovoltaic and solar thermal systems. Therefore the system is restricted to supporting decisions on energy efficiency measures, while energy generation solutions are not considered. The scope of this work is to address this problematic by defining the design problem of a solar system component and further by providing a description of what is to be built and how it is expected to be built in order to allow for software development to proceed with the implementation. Two main issues are addressed, design optimization and seamless integration into a building design system (SEMERGY). This research determines the exact problem and its parameters, and investigates existing tools for active solar design in order to explore whether and how they answer the specific design problem. Further, it develops the design specifications in accordance with user requirements, defines the system architecture and the detailed computer system models, and executes test cases in order to test how the tool responds to the design specifications. Finally, the interaction with SEMERGY environment is analyzed and the necessary extensions to SEMERGY Building Model (SBM) are reported. The design tool points to design solutions that achieve an optimum exploitation of the available area of the building envelope. Optimization is evaluated against preset design criteria for maximizing CO2 reduction gains and financial performance. As a result, the implementation of the solar system component enhances the optimization function of SEMERGY, since it allows the user to be able to design buildings with more specific requirements.