Comparison of off-grid power supply systems using lead-acid and lithium-ion batteries

Solar home systems (SHS) and solar photovoltaic village power supply systems can play an important role in the supply of electrical energy to off-grid areas. This paper presents a comparison of solar home systems and village power supply systems using two different types of battery technologies, namely lithium nickel cobalt aluminum oxide (NCA) and lead-acid (Pb) batteries. The developed models were implemented in Matlab/Simulink where solar radiation, temperature and electrical load data from Dodoma, the capital of Tanzania were used as model inputs. Two topologies were analyzed for SHS: A system which is directly coupled to the battery and another system which uses a Maximum Power Point Tracker (MPPT) charge controller. The main idea of analyzing these two topologies was to find an affordable solution for off-grid population, but at the same time the selected topology should have the ability of extracting maximum output from the PV panel. Since most of the off-grid settlements in Tanzania today use SHS with lead-acid batteries as storage, analysis was carried out for SHS with lead-acid batteries and SHS with lithium-ion batteries by simulating and optimizing the systems for 20 years. The levelized cost of electricity (LCOE) for both storage systems was compared and it was found that the SHS with lithium-ion (NCA) battery generally had a lower LCOE compared to the SHS with lead-acid battery. This is mainly due to both the longer life time of NCA batteries and the reduction of the price of NCA batteries as a result of significantly increasing global production scales. For the case of solar photovoltaic village power supply systems, an energy management system was implemented to optimize power flows in a hybrid storage system containing both lead-acid and lithium-ion batteries. Optimization of this "hybrid" system led to a selection of both types of batteries with small capacity of lead-acid battery (0.24 kWh) compared to NCA battery (1.44 kWh) backed up with diesel generator. Further analysis was done regarding the benefits of village power supply systems over individual SHS, and it was found that the LCOE for solar PV village power supply systems was lower than the LCOE for single SHS.