Model of a hybrid distributed generation system for a DC nano-grid

A large segment of the world's population lives in rural areas that are geographically isolated, remote and sparsely populated. Nano grids employing hybrid energy systems (HES) based on photovoltaics (PV) and wind farms are considered to be an effective option to electrify remote and isolated areas which are far from conventional grids. This is applicable to areas that receive high averages of solar radiation and sufficient average wind speed annually. In this research investigation, a DC nano-grid was modelled, simulated and optimized for a hybrid solar-PV and wind, with energy storage and a back-up diesel generator for Umzinyathi district in KwaZulu-Natal Province, South Africa. A site survey was conducted, wind resource and solar radiation data obtained for the purpose of load forecasting and system modelling. HOMER software was used for system modelling. Minimum cost optimization of the system was carried out taking into consideration the costs of system components, hourly solar radiation and rating parameters as inputs into the simulation program. Sensitivity variables were specified to examine the effect of their uncertainties on system performance. Based on simulation results, the optimal system comprises of a 100kW PV array, thirteen 7.5kW wind turbines, 20kW diesel generator, and 96 Trojan T-105 deep cycle batteries. The net present cost (NPC), cost of energy (CoE) and payback period of the optimal system were found to be $459 545, $0.248/kWh and 4 years respectively. The economic and environmental analysis indicated that it is more advisable to electrify remote settlements using a DC nano-grid based on hybrid systems with multiple renewable sources as they have lower operating costs and more environmental friendly due to the reduced dependence on diesel generating units.