Investigating PV module failure mechanisms caused by indirect lightning strikes

Coetzer, Michael Kurt (2019-04)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: There is an ever increasing global adoption of solar photovoltaic (PV) technologies as sources of renewable energy due to an increasing worldwide energy demand, the depletion of fossil fuel reserves, the shift towards environmentally friendly sources of energy, and an increasing supply, coupled with a decreasing cost, of solar PV technologies. Lightning poses a significant risk to person and property, with some experts estimating a global increase of up to 100% in the level of lightning activity for every 1 °C rise in average global temperatures. An increasing implementation of solar PV technologies and an estimated increase in global lightning activity create cause for concern for solar PV plant owners. Repair log data from three utility-scale solar PV power plants was examined, and occurrences of the failure of bypass diodes were noted. An impulse generator was designed and constructed in order to ascertain the failure modes of a bypass diode. Once this understanding was gathered, metal-oxide varistors (MOVs) were investigated as a suitable bypass diode protection measure. An appropriately chosen MOV was found to protect a bypass diode to a level at least double that of the level at which the bypass diode would normally fail. Computational electromagnetic simulations were performed in order to investigate how the geometry of a PV module, and module interconnections, may in uence the extent to which currents may be induced within a PV installation. From simulations, it was found that the presence of the continuously conductive frame of a PV module greatly reduced the net magnetic ux passing through the module, reducing the magnitudes of the induced currents. A reduction of 40% in the magnitudes of the currents induced within the inter-module wiring was observed in a simulation with multiple series-connected PV modules. Neater inter-module wiring, with a smaller loop area, reduced the magnitude of the currents induced within the inter-module wiring by between 93% and 98 %. Testing was performed in a high-voltage laboratory in order to establish the extent to which currents may be induced within an actual PV module. The testing concluded that although a current may be induced within the internal traces of a PV module, it is loop areas within the inter-module wiring which are most likely to result in the induction of currents within the PV installation. Good wiring practice should therefore be applied during the installation of PV systems in order to reduce the formation of loop areas which magnetic fields may couple into.

AFRIKAANSE OPSOMMING: Daar is 'n globale toename in die gebruik van fotovoltaïese (FV) sonkrag as 'n bron van hernubare energie weens die toenemende w^ereldwye aanvraag na energie, die uitputting van fossielbrandstofreserwes, die oorgang na omgewingsvriendelike energiebronne en 'n toenemende beskikbaarheid, tesame met dalende kostes, van sonkrag FV tegnologiè. Weerlig is 'n beduidende risiko vir mense en eiendom, met sommige kenners wat 'n globale toename van tot 100% voorspel rakende die vlak van weerligaktiwiteit vir elke 1 °C styging in gemiddelde globale temperature. 'n Toenemende implementering van sonkrag-tegnologië en 'n beraamde toename in globale weerligsaktiwiteit veroorsaak rede vir kommer vir FV-aanleg eienaars. Historiese instandhoudingsdata van drie grootskaalse FV-sonkragstasies is bestudeer en voorvalle can omloop-diode falings is waargeneem. 'n Impulsgenerator is ontwerp en geïmplementeer om die faalings-modusse van 'n omloop-diode te bepaal. Met die verstaan van die begrip, is metaaloksied-varistors (MOVs) se geskiktheid as 'n omloop-diode beskermingsmaatreël ondersoek. 'n Geskikte MOV kan 'n omloop-diode beskerm tot 'n maksimum van tweemaal die vlak waarby die omloop-diode normaalweg sou faal. Elektromagentiese-simulasies is uitgevoer om te ondersoek hoe die dimensies van 'n FVmodule, asook die tussenverbindings, moontlik die vlak waarmee strome in die FV installasie geïnduseer kan word beïnvloed. Vanaf hierdie simulasies is daar gevind dat die teenwoordigheid van die kontinue en geleidende raam van 'n FV-module grootliks die resulterende netto magnetiese-vloed verminder het, wat gevolglik ook die grootte van die geïnduseerde strome verminder het. Verder is 'n afname van 40% waargeneem vir die strome wat geïnduseer word tussen die kabelverbindings van verskeie serie-gekonnekteerde FV-modules. Daar is ook bepaal dat 'n sorgvuldige benadering tot kabelverbindings tussen FV-modules, met 'n kleiner lus-area, die geïnduseerde stroomgroottes verminder met tussen 93% en 98 %. Toetse was uitgevoer in 'n hoë-spannings-laboratorium, sodat die omvang van geïnduseerde strome binne in 'n FV-module vasgestel kon word. Daar is vasgestel met hierdie toetse dat, alhoewel 'n stroom waarskynlik geïnduseer kan word in die interne FV-sel konneksies van 'n module, die lus-areas van die kabelkonneksies 'n groter effek het op die geïnduseerde

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105952
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