A system voltage-induced degradation (SVID), also known as a potential-induced performance degradation (PID), occurs in crystalline photovoltaic (PV) modules and is caused by stray currents, causing power loss of up to 30%. Depending on the type and design of solar cells, SVID affects PV modules to varying degrees. Specifically, the PV modules towards the end of a string within a PV system are at a high potential difference from the module’s frame, leading to a strong potential field within the module and subsequent leakage currents through the module packaging materials. The extent of the leakage current is an important parameter to monitor because it is often an indicator of the degree of SVID. Although measurements of the total leakage current are possible, it is not currently feasible to pinpoint leakage currents from each individual pathway.
UCF researchers have invented a diagnostic device, a custom laminate, which independently measures, as a function of time, the respective electrical resistances of various electrically-conductive pathways created in a PV module. The device can also study design modules as a whole.
Electrodes are placed in specific locations and measure leakage currents in various pathways, including the bulk encapsulant, the front cover, the front and back cover encapsulant interfaces, and the surface of the front cover in a PV module. The invention consists of two diagnostic devices. Device A measures internal interface and bulk pathways and is comprised of a laminate which is similarly structured to a PV module with a front cover, encapsulant, and a back cover. Device B measures bulk resistivity and surface sheet resistance of the front and back covers.
This method can be used in an accelerated testing environment as well as in the field to study the performance and degradation of various PV module materials under high voltage bias. This device can be used in testing laboratories and PV manufacturing companies for testing PV modules in hot and humid climates, or in damp heat chambers with a high voltage bias, providing a detailed diagnosis of the moisture ingress in addition to leakage currents and its negative effects. Accelerated PV testing for degradation will help optimize the PV design to decrease leakage currents and hence decrease degradation of PV cells and increase efficiency.
- Pinpoints leakage currents in PV systems
- Useful in hot and humid climates
- Accelerated testing environments
- Laboratory testing
- Field testing
- PV manufacturing