Researchers from the University of Miyazaki in Japan used a new non-destructive method to enable them to investigate solar cell vibrations independently of module components. The study included potential design characteristics for resonance-resistant vehicle integrated PV modules that would increase the natural resonance frequency to more than 2,000 Hz.
Researchers at the Japanese University of Miyazaki used a new non-destructive, doppler laser-based method to investigate the effects of vibrations on solar cells embedded in a vehicle-integrated PV (VIPV) module, regardless of the car roof and the module components. The study also investigated the potential to design resonance-resistant VIPV modules.
“As far as I know, no one has previously considered that the solar cells can vibrate in the module and can resonate independently of the modul structure. This article is the first to provide measurement certificate that can resonate solar cells in the module at their natural resonance frequency,” said the corresponding author Kenji Araki said PV Magazine.
The team reported that, unlike static installations in buildings experienced vibration frequencies, ranging from 0.1 to 1 Hz, the vibration frequencies of PV systems are moving in the range of 1,000 Hz for trucks and 2,000 Hz for passenger cars.
In this range, the soft resins of the ethylene vinylacetate (EVA) molecular chain movement do not dampen the vibrations according to the scientists. Despite the low damping factor of the EVA, the vibration tests did not reveal cell cracks.
“In our measurements and studies, we have found that resonant vibrations did not cause catastrophic stress that would cause cell ractures. Recent studies into micro-electromechanical systems (MEMS) devices suggest that crystalline siliciums silicium can show in Piezo-Material in Piezo-Material Piezo-Mems in Piezo-Mems and Pols in Piezo-Mems in Piezo-Mems in Piezo-Mems in Piezo.
“This means that even if the stress level is lower than some cracks in solar cells, we must be careful because increased dislocation density of cyclical stress can lead to rapid performance when moving PV applications,” he said.
The non-destructive method used to measure the vibrations was based on a Laser Doppler vibrometer (LDV). The use of a contactless measuring approach was “essential” to prevent the weight of the sensor head to be added to lightweight objects, such as solar cells, explained the scientists.
They also used silver stickers and micro-mirrors on the cover glass to prevent the extensive heads of the laser units from interfering, making individual vibration measurements of the glass and cells possible.
The Laser Doppler technique was able to detect the independent vibration movement of a solar cell, also that the glass/EVA lamination resonates independently and that the resonance frequency is close to the natural resonance frequency of the car roof. The measurements confirmed that the roof of the motorcycle vibrates up to 2,000 Hz, as defined in the vibration test conditions in IEC 17650–3: 2023.
In the light of the results, the researchers noted that eliminating the vibration source is not practical, but design adjustments can increase the natural resonance frequency above 2,000 Hz by, for example, increasing the number of tabbons of the tabs.
The research team is now investigating the impact of cyclical stress on flexible PV modules, including how the modules deal with stress during rolling and transport, as well as the interaction between vibration stress and the local deformation of curved solar cells, according to ARAKI.
“Moreover, we are developing a contactless inspection method to detect wrinkles or other local curves in solar cells, which are often seen in curved modules,” said Araki.
The work has been documented in “Direct detection of vibrations and resonance of the solar cells in vehicle-integrated photovoltaic modules“Published in Solar energy materials and solar cells.
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