Most of the research on Hybrid Power Systems (HPS) is to provide an economical and sustainable power to the rural electrification. This paper focuses on the design of an HPS for the building which is a part of the urban electrification. In the developing countries, the rate of increase in the demand is more than the rate of increase in the supply, which is a major challenge resulting in very frequent outages. There are number of motives to build integrated and synergistic renewable energy based HPS including environmental, economic, and social benefits. Most of these HPS topologies use inverters to interface the renewable sources to the buildings with an offering of low quality power. Hence, modern sustainability initiatives call for a design for both new HPS and retrofitting of an existing HPS topology. With this aspect, this paper describes the topology of retrofitting HPS with dc Motor-Synchronous Generator set instead of the use of inverter to an existing building power system. This can improve the power quality, reliability of the supply, and ensures stable plant operation. The proposed HPS topology can be used in small-to-medium sized isolated constructions like green buildings, industries, and universities. Different renewable energy sources like Photo Voltaics (PV), Wind Power (WP), and Fuel Cells (FC) are integrated to form HPS. An energy management and control algorithm is proposed to use the energy sources optimally to upgrade these buildings with more reliability and efficiency. The modeling and simulation is done using MATLAB/Simulink.