This study presents the modelling and optimization of a Hybrid Energy System (HES) for GSM Base Transceiver Station (BTS) sites in emerging cities. The aim is to ensure reliable and cost-effective power supply, considering the availability, dynamism and viability of energy sources.
Theoretical approach is applied in the modelling, simulation and validation of the developed HES, which consists of the utility grid, wind and solar photovoltaic (PV) as primary energy sources incorporating a super-capacitor/battery storage and power conversion unit. The complexity in optimizing continuous variables of the HES informed the use of a hybrid Genetic Algorithm and Pattern Search (h-GAPS) technique. The optimization problem is treated as a single objective function by considering all objectives in terms of cost while constraining the HES to satisfy the load demand safely according to the reliability criteria defined by the energy management strategy. The h-GAPS based optimization model simulated for the peripheral node GSM BTS sites in Abuja, Benin City, Enugu, Ikeja, Maiduguri and Sokoto utilized long-term (22-years) meteorological data sets collected from the Nigerian Meteorological agency and the National Aeronautics and Space Administration. The performance index of various developed and existing energy systems is evaluated based on economy or Cost of Energy (COE), power system reliability, energy throughput, and emission reduction targets.
Simulation results showed that Sokoto is the most favourable site for utilizing the proposed HES. Abuja and Benin City are the least favourable locations for utilizing the grid-connected (Grid/PV/Wind) and the off-grid (PV/Wind) configurations respectively. The optimum size of grid-connected HES consisting of 2 kW wind turbine, 7.09 m2 PV array inclined at 150, 0.053 kWh super-capacitor and 10.8 kWh (48V, 225Ah) battery banks, and 1,484.60 kWh of energy drawn from the grid per annum enabled reliable (negligible power loss) and cost-effective energy supply in Sokoto. The off-grid configuration reduced the COE by 72.81% (N24.75 to N6.73 per kWh) but with larger PV array size (12.68 m2) and reliability of 99.02%. In comparison with current practice of using grid/diesel systems, the proposed off-grid configuration has the best performance index, with an average energy throughput of 0.076 kWh per naira, in Nigeria. A reliable and cost effective energy option will not only reduce the per-unit cost of mobile services in Nigeria, but also reduce the greenhouse gas emission level from GSM BTS sites by an average of 98.34% thereby making the environment much more friendly and safe. This research would be useful for mobile service providers, consultants, regulatory agencies, policy makers, and the society.