Caracterización y optimización de parámetros de dispositivos fotovoltaicos. Aplicación a la industria

Resumo

The optimization and characterization of parameters of photovoltaic (PV) devices involves a wide number of aspects all of them aimed to the improvement of the efficiency of PV Energy. For that purpose, this thesis has focused in three fundamental subjects: 1. STUDY OF PARALELL RESISTANCE (RP) AND ITS CHARACTERIZATION IN SOLAR CELLS AND PV MODULES. A new method to measure the module shunt resistance (Rp) by measuring the module at reverse bias and dark conditions connected to an external parallel resistance is presented. For the purpose of proving this method, two modules, MA and MB, (with the same type of cells and the same efficiency, but different shunt resistance) were manufactured. The module Rp has been determined with the proposed method and results have been compared with I-V curve measurements obtained with commercial Solar simulators and other standard procedures. Additionally, modules MA and MB were measured at different irradiance levels to relate the Rp with the module performance at low irradiance conditions. Finally, in order to evaluate the relative importance of a correct determination of the module Rp, a simulation of Annual Energy Yield obtained with an installation made with modules MA compared with modules MB have been carried out by means of PVsyst program. 2. ESTUDY OF THE INFLUENCE OF MISMATCH OF SOLAR CELLS ON RELATIVE POWER LOSS OF PHOTOVOLTAIC MODULES. This work presents a study of mismatch losses when solar cells are associated in series to form photovoltaic (PV) modules. In this experiment, more than 10,000 single-crystal and multi-crystal cells were measured and sorted in groups, according to cell maximum power (Pm), maximum power point current (Imp) and short circuit current (Isc). Afterwards, PV modules were manufactured and measured with cells from each group. A selection of single-crystal cells with an efficiency rate of 17,75 % was studied with results showing low relative power loss (RPL) rates. This was the case even when artificially increasing the scattering of mentioned electrical parameters. Due to these results, a second choice was made to perform a similar comparative study of multicrystal cells. In the second study, the multi-crystal cells showed a greater scattering of electrical parameters in groups of a 14,57% efficiency rate and of a 14,23% rate. In that case, results obtained for both groups showed a relation between RPL and standard deviation of electrical parameters. Despite there already being a widely recognized definition of RPL, due to the increased volume of cells in production environments, which is where this study was performed, the need was found for more effective and practical expression of RPL due to the large quantity of samples. Consequently, this study proposes an innovative statistical equation of RPL relevant for the growing needs in this sector which can handle the parameters usually available to a module manufacturer. This equation is theoretically validated by comparison with Bucciarelli´s results (1979). The proposed expression of RPL has been applied to this study and an empirical relation between RPL and standard deviation of solar cell parameters has been obtained. 3. ESTUDY OF THE QUALITY OF THE TEXTURE OF SINGLE-CRYSTAL SOLAR CELLS AND ITS CHARACTERIZATION. In this third aim, the chemical process for solar cell texturing has been carried out in the laboratory and compared with the one carried out in a manufacturing line. Different process parameters, such as wafer quality and time, have been changed to optimize the process. A new method for measuring the surface texture of single-crystal wafers has been developed. This is based on an incident laser beam directed towards the surface at a normal angle. They light reflected pattern so obtained exhibits 4-fold symmetry with intensity maxima at well-defined off centre angular positions. The relation between the spatial light pattern and the geometrical features of the texture is discussed. A method and device that relate the reflected intensities with the texture degree is developed and tested. The developed method permits its implementation in industrial environments due to its reproducibility, reliability and low cost.