Photovoltaik system design and optimisation with li-ion battery storage for residential applications in Afghanistan

Converting solar power directly into electricity with simple construction techniques but without producing any greenhouse emissions are the crucial reasons for using PV systems. In the present thesis, a study of design and optimization is carried out for meeting the electricity requirement of an off-grid family house in Kabul (Afghanistan) by way of a stand-alone photovoltaic energy system with lithium-ion battery storage. Towards this end, yearly solar radiation data on an hourly basis are used together with two different load profiles representing the energy requirement of a family house. Using current-voltage (I-V) curve based analytical model for the PV and a state of charge (SoC) based model for the battery, the loss of load probability (LLP) is calculated and used for optimization of the energy system together with the life cycle cost (LCC) of the system. Various battery capacities are used for the optimization purpose; from zero storage (with no battery capacity) through to two-day storage, including half-day storage, one-day storage and two-day storage capacities. MATLAB and EXCEL programming languages are used in coding the models and solving the equations. The solutions of the equations for the energy system are carried out using the PV and battery parameters and also the load demand data that the system has to meet. The energy system analysis is performed by considering the possible states of energy generated, energy stored and the energy demand. In this regard, if the amount of energy generated by the PV panels is greater than the energy demand, then the load is met and the excess energy is stored in the li-ion battery. If the PV panels do not produce enough energy to meet the load but there is sufficient energy stored in the battery, then the load will be satisfied and the system will work continuously. Finally, if the PV panels cannot produce adequate energy and there is no energy or sufficient energy stored in the battery, then the load cannot be covered, either partially or completely. In this context, the performance of the system with different combinations of number of PV modules and battery capacities are analyzed in detail and the optimum combinations are determined accordingly. With one and two-day storage capacity for a value of 0.035 and 0.040 LLP, the optimum performance and efficiency are achieved with 30 and 50 modules for the first and second load profiles respectively.