Optimum load matching in direct-coupled photovoltaic power systems

This research is concerned with the study and analysis of a direct-coupled photovoltaic power system composed of a solar array and electrical loads. In this system the power produced by the array passes directly to the loads. An electric battery may be employed to supply the loads during short periods of time.; The objective of this study is to define a quantitative measure for the quality of load matching to the photovoltaic array, study the parameters affecting the load matching and optimize the transfer of energy to the loads.; A load matching factor is used for this purpose as the ratio of the load energy to the array maximum energy in a one day of sunlight exposure. A theoretical analysis leading to a general mathematical formulation of the load matching is presented. A non-linear optimization approach is used to solve the load matching problem with the objective of maximizing the load matching factor, and consequently the photovoltaic output energy. This approach is then applied to different types of electrical, electrochemical and electromechanical loads connected to the photovoltaic array. The solution of the optimization problem yields the optimum matching factor and the corresponding optimum load parameters. In order to obtain general quantitative results a per unit system based on the array maximum power point parameters is adopted. The study takes into consideration the effect of varying the temperature of the array and the loading parameters. Sensitivity analyses are performed to study the effect of varying the load parameters on the matching factor. A battery of selected parameters can be included if the load characteristic results in poor matching performance.; The results show that optimum matching can be achieved by carefully selecting the array parameters with respect to the load parameters. The array temperature has little effect on the optimum matching factor. However, the optimum matching parameters are greatly affected by the array temperature. A maximum power tracker may not be needed if optimum or near optimum matching is achieved. The results should solve the problems related to the optimum size of the array needed to supply the connected loads in direct-coupled photovoltaic power systems.