The foreseeable large-scale deployment of intermittent renewable energy systems in the future and fluctuations in energy markets can severely affect the operation and stability of smart grids, creating significant uncertainty and instability in the electricity supply and demand. It is believed that the mismatch between energy demand of a building and instantaneous renewable energy generation can be reduced by controlling energy use through the energy flexibility of the respective building. Enhancing the energy flexibility of a zero-emission building can satisfy the demands of the energy network around the building and contribute to the resilience of the energy system. Meanwhile, in an electricity tariff model with a distinction between peak and off-peak periods, enhancing energy flexibility in buildings can reduce the operating costs of electricity consumption, with benefits to the economic performance of the building itself. In this study, a simulated hypothetical zero-emission office building near the coast with a floating photovoltaic system and tidal stream generator system in Hong Kong from previous study were used in a case study to investigate the impact of energy flexibility control with stationary batteries as the source of energy flexibility. Two flexibility control strategies were designed to demonstrate their impact on the economic performance of the system. After incorporating the “Peak Demand Management” (PDM) programme in Hong Kong, variations in the economic performance of the system were demonstrated through simulations. Considering the incentive provided by the PDM programme, the possibility of achieving a neutral economic performance at different percentages of renewable energy generation over a 20-year life cycle without the feed-in tariff was investigated. Furthermore, two possible modifications for business models and the PDM programme are proposed. The simulation results indicate that both suggestions can significantly improve the economic performance of the system.