Approximation of current-voltage characteristic of ventiled solar battery

Abstract

The current-voltage characteristic is the main functional characteristic of the solar battery. It allows you to determine the optimal, in terms of transferring maximum power to the load, the mode of operation of the solar battery. Theoretically, the current-voltage characteristic of a valve photocell is described by a system of non-linear differential equations of the 5th order with the corresponding boundary conditions. The system of equations is the balance of electrons and holes inside the valve photocell. The distribution of the electric field strength is described by the Poisson equation. An analytical solution of this system is possible in two cases – for the “thin” p-n junction and for the p-n junction, inside which the processes of generation and recombination of charge carriers can be neglected. The analytical solution in this case is the Ebers-Mall equation, which interconnects the current, voltage in the load and the parameters of the photocell – photoemf, photocurrent, saturation current, thermal potential. In the general case, the system of equations is solved by numerical methods. In the literature, numerical results are represented by the Ebers-Mall equation, in which the coefficient a = 1 - 5 is introduced. An experimental-calculation method for determining the parameters of the photocell and coefficient a is proposed. Some parameters of the photocell can be measured in the process of taking the current-voltage characteristic – photoemf in idle mode and photocurrent in short circuit mode. The least squares method was used to determine the parameter a and the saturation current from the experimental data. The proposed method for approximating the current-voltage characteristic is applied to several silicon polycrystalline solar batteries.