The Effect of Shadow Lines on a Low Concentrating Photovoltaic System

摘要

In order to reduce the energy losses caused by shadow lines, three options are investigated. These are: 1. the use of two types of diodes; 2. the use of an "ideal" diode based an active bypass by using MOS-FET's [4] and 3. parallel switching of a number of cells between two shadow lines. The first method can reduce the voltage losses of the diode to about 300mV when oversized Schottky diodes are used. With the second method it is possible to reduce the voltage losses further to about 60mV for FETs with a resistance of 3m. This method has as disadvantage that more electronic components are required to control the FET. With the third method about 10 cells are placed in parallel in one module. In that case only one shadow line appears on each module. Series connection of these parallel modules will result in zero energy losses because no bypass diodes are needed at all. This method has as a disadvantage of very high current output of the module of up to 200A. In a model, the three methods are further analyzed with respect of power losses and costs. The effect of the degree of shadowing on the daily energy yield and hence the fill factor is simulated with a model of the PV module. These results can be used in the design of the circuit of the ideal bypass diode.