| Work Detail |
A Swiss research group has improved the hail test bed to measure the impact of ice balls of greater diameter and speed on solar panels. The new testing method appears to allow solar panel manufacturers to evaluate their products with adequate safety margins.
Scientists from the University of Applied Sciences and Arts in Southern Switzerland have developed a novel hail test for photovoltaic panels that takes into account the impact of large ice balls at high speed.
The research team highlighted that traditional hail tests carried out according to the IEC 61215-2 standard usually evaluate the impact of ice balls with a diameter of 25 mm and a speed of 80 km/h. However, he also noted that the Swiss Association of Cantonal Fire Insurers - the Vereinigung Kantonaler Feuerversicherungen (VFK) - set a minimum requirement of 30/40 mm and added that the Swiss laboratory SUPSI PVLab is currently planning to create a hail test bed that reach 100 mm in diameter and 166 km/h speed.
“Increasing the diameter of the ice ball requires evaluation of sample preparation, repeatability and representativeness, as well as the ability to handle high velocities with high masses to reduce uncertainty in impact energy, as required by standards.” Swiss,” the researchers noted.
They used a Hopkinson bar and a 30 mm aluminum bar to analyze the waveform resulting from the collision of the ice balls. They also used a strain gauge station, a gas gun to accelerate the ice balls, and a camera to record quick images.
The gas gun was designed to fire 25mm, 40mm and 70mm diameter ice balls onto the Hopkinson bar. “A round plexiglass tube with different interior diameters was used to guide the spherical ice inside,” the researchers explained. “To measure the velocity of the spherical ice samples, a laser sensor was placed at the end of the tube.”
The academics fired the three balls at the same speed and at two different freezing temperatures, -5ºC and -20ºC, to compare the response of charge versus time.
Analyzing the 40 mm diameter samples, they verified that the decrease in temperature caused a double loading rate, which in turn caused a higher stress rate in the bar.
“In the case of ice balls of 25, 40 and 70 mm at -20 ºC, the maximum forces are approximately 70%, 59% and 44% higher than those at -5 ºC at the same speeds,” they further explained. . “For 25, 40 and 70 mm, the ice reaches its maximum strength in a shorter time at -20 ºC, which is 30%, 21% and 2% less than at -5 ºC.”
The analysis showed that a lower temperature results in a higher maximum force and a shorter maximum time. “With these preliminary results, the project will advance its future tasks, which include the analysis of damage caused by hailstones using a multispectral camera, the analysis of photovoltaic panels of different ages, the mechanical characterization of ice in the same range of deformation rate and FEM modeling of the phenomena,” the scientists conclude.
Their results are presented in the study “ Advanced characterization of photovoltaics for hail resistance,” published in Materials Letters . |
