Optimum design of an off-grid hybrid renewable energy system for an office building

Although much attention has been paid to the utilization of hybrid renewable energy systems for either commercial buildings or residential ones, rare studies dealt with the application of off-grid hybrid renewable energy systems for commercial buildings. This paper presents a comprehensive study on the techno-economic performance of a stand-alone hybrid photovoltaic (PV)-wind-battery system for an office building located in Tehran, Iran. The Hybrid Optimization Model for Electric Renewables model was used to investigate the optimal design options and the techno-economic viability of the hybrid renewable energy system installed in that building. The proposed hybrid system based on renewable resources was designed to electrify the restrooms of the building. An optimal system configuration was chosen based on the total net present cost (NPC) and cost of energy (COE). The simulation results demonstrated that the optimum structure for the hybrid system for the primary load demand of 5.6 kW h per day, consists of 3 kW PV modules, 1 kW wind turbine, 1 kW inverter, and sixteen 200 A h batteries. The total NPC of such a system was estimated to be $21 132, while the COE was $1.543 per kW h. In addition, the proposed hybrid energy system could provide 2733 kW h additional electricity to the office building. Furthermore, in the last part of this research, a sensitivity analysis for different parameters such as primary load, wind speed, global solar radiation, interest rate, total NPC, cost of electricity, number of batteries and total electrical production was performed to demonstrate and elaborate the effect of each decision variable on the configuration of the optimum hybrid system. It became clear that two hybrid system configurations, i.e., PV-Wind-Battery and PV-Battery systems, are suggested as the most economical and feasible alternatives and have wide range of usage for different load demand values. Additionally based on the change in the initial design parameters such as wind speed, global solar radiation, load demand, and the real interest rate, a comparison between these two hybrid systems in terms of the total NPC, COE, electrical production, excess electricity, and grid extension distance has been made to investigate the effect of each decision variable on the optimal combination and the techno-economic viability of the hybrid renewable energy system.