# Effects of Climate and Environmental Conditions on the Operation of Solar Photovoltaic Generators

##### Lappalainen, Kari (2013)

Lappalainen, Kari

2013

Sähkötekniikan koulutusohjelma

Tieto- ja sähkötekniikan tiedekunta - Faculty of Computing and Electrical Engineering

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##### Hyväksymispäivämäärä

2013-04-03**Julkaisun pysyvä osoite on**

http://urn.fi/URN:NBN:fi:tty-201304061108

##### Tiivistelmä

Photovoltaic (PV) generators are composed of series- and parallel-connected PV modules. The series connection of PV modules increases the voltage level and a parallel connection increases the current level of the generator. In grid-connected applications, high voltage levels are needed for interfacing equipment used for connecting PV generators to the utility grid. Partial shading has harmful effects on the operation of PV generators and a series connection is more prone to these effects than a parallel connection. One of the major effects is the occurrence of mismatch losses, which are the difference between the sum of the maximum power outputs of individual modules and the output of the system. In practice, some mismatch losses occur always.

In this thesis, the effect of the configuration of a PV generator on the operation of the generator under partial shading conditions is discussed. The objective of this thesis is to study the shadow sensitivity of different configurations of a PV generator. First, the basics of solar radiation are introduced. After that, the operation principles of PV cells and configurations of PV generators are discussed. The simulation model of a PV generator is made in this thesis by using the MATLAB Simulink software and it is verified by measurements. The shadow sensitivity of series-parallel (SP), total-cross-tied (TCT) and multi-string (MS) configurations is studied by using the simulation model. All the studied configurations have an array in the shape of a square and are connected to the utility grid by one centralized inverter. The shadow sensitivity of configurations is studied with three movement directions of shadows: perpendicular to the PV module strings of a PV generator array, parallel to the strings of the array and diagonal to the array. In addition, the sharpness of a shadow is varied.

The simulations showed that the mismatch losses of a PV generator are smallest when a shadow is moving perpendicular to the strings of the generator array. In that case, the MS configuration has no mismatch losses and the mismatch losses of the SP and TCT configurations are equal and almost negligible. When a shadow is moving parallel to the strings of a PV generator array, every configuration has equal mismatch losses. When a shadow is moving diagonal to a PV generator array, at the generally used sizes of PV generator arrays, the MS configuration has substantially smaller relative mismatch losses than the SP and TCT configurations. The difference between the mismatch losses of the SP and TCT configurations is quite small. Based on the simulations, the MS configuration has the lowest shadow sensitivity. However, during equal conditions, the efficiency of the MS configuration is somewhat lower than the one of the SP and TCT configurations due to DC-DC converters. The size of the PV generator array and the cloudiness of the district determine which configuration is the most functional. Based on the simulations, a PV generator should be located so that the dominant direction of clouds is perpendicular to the strings of the generator array.

In this thesis, the effect of the configuration of a PV generator on the operation of the generator under partial shading conditions is discussed. The objective of this thesis is to study the shadow sensitivity of different configurations of a PV generator. First, the basics of solar radiation are introduced. After that, the operation principles of PV cells and configurations of PV generators are discussed. The simulation model of a PV generator is made in this thesis by using the MATLAB Simulink software and it is verified by measurements. The shadow sensitivity of series-parallel (SP), total-cross-tied (TCT) and multi-string (MS) configurations is studied by using the simulation model. All the studied configurations have an array in the shape of a square and are connected to the utility grid by one centralized inverter. The shadow sensitivity of configurations is studied with three movement directions of shadows: perpendicular to the PV module strings of a PV generator array, parallel to the strings of the array and diagonal to the array. In addition, the sharpness of a shadow is varied.

The simulations showed that the mismatch losses of a PV generator are smallest when a shadow is moving perpendicular to the strings of the generator array. In that case, the MS configuration has no mismatch losses and the mismatch losses of the SP and TCT configurations are equal and almost negligible. When a shadow is moving parallel to the strings of a PV generator array, every configuration has equal mismatch losses. When a shadow is moving diagonal to a PV generator array, at the generally used sizes of PV generator arrays, the MS configuration has substantially smaller relative mismatch losses than the SP and TCT configurations. The difference between the mismatch losses of the SP and TCT configurations is quite small. Based on the simulations, the MS configuration has the lowest shadow sensitivity. However, during equal conditions, the efficiency of the MS configuration is somewhat lower than the one of the SP and TCT configurations due to DC-DC converters. The size of the PV generator array and the cloudiness of the district determine which configuration is the most functional. Based on the simulations, a PV generator should be located so that the dominant direction of clouds is perpendicular to the strings of the generator array.