Electric field distribution in PV modules

IntroductionCompact photovoltaic module is a layered structure consisting of interconnected and encapsulated solar cells embedded between substrat and superstrat (back and front sheets), glass or plastic sheets, in order to... [ view full abstract ]

Introduction

Compact photovoltaic module is a layered structure consisting of interconnected and encapsulated solar cells embedded between substrat and superstrat (back and front sheets), glass or plastic sheets, in order to create compact and sealed unit protected against environmental influences. Solar cells strings are encapsulated between two sheets of encapsulant foil. In the case of many solar cells connected into series, the encapsulant is electrically stressed mainly at sharp edges of the structure. Another source of enhanced electric field is accumulation of space charge at the dielectric – electrode interfaces. This phenomenon is connected with the electrode polarization [1]. In the process of polarization the free cations in dielectric are accumulated near the negative electrode, creating a positive charge. A similar process runs near the positive electrode. The steady state of accumulation is given by the balance of concentration gradient and the Coulombic (electric) force [2, 3].

Methods

Interfacial processes were studied in various insulation foils intended for encapsulation of photovoltaic cells. The analysis was based on the dielectric measurements in a broad region of temperatures and frequencies. The measurements showed that the observed processes are connected with the electrode polarization. The electrode polarization gives rise to the space charge formation and enhancement of electric field near the electrodes.

Results and Discussion

Calculation of the electric field is important for praxis as it allows assessing the risk of electrical break-down. In our work we use the parameters obtained from the dielectric meas-urements for calculation of electric field distribution in encapsulating materials. It was found that electric field increases more than 100-times comparing with the mean value.

Dielctric parameters permittivity ε, conductivity σ, thicknesses of Debye layer assigned as h₁ and the bulk layer h₂ and electric field ratio E₁/E₂ which equals to s₂/s₁ are in Tab. 1. for various temperatures.