During 30 years on a rooftop, a solar panel gets bombarded by UV rays, soaked by rain, buffeted by wind, pounded by hail.
How well it stands up to that beating is a crucial factor in setting the warranties of solar modules – and in convincing the public that solar energy can be counted on like the sun rising in the east.
The U.S. Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL) plays a crucial role in improving the reliability of the photovoltaic (PV) panels that are being installed on rooftops in record
NREL helps set standards for reliability and serves as a neutral third party in tests of manufacturers’ new solders, edge seals, and glues. At its Golden, Colorado, campus, NREL subjects solar panels to heat, humidity, and mechanical stress to simulate conditions in Denver, Phoenix, the Philippines, and elsewhere.
In March, leading scientists and engineers in the industry gathered at NREL for the PV Module Reliability Workshop. The workshop encouraged a frank discussion of reliability problems that can plague solar power companies.
What standards are needed for the glue in the edges that seal a panel’s top and bottom? How does weather affect cracking? What can be done to prevent one glass panel from creeping away from the other?
NREL Stresses Edge Seals to Predict Failure
Solar modules must be sealed to keep out moisture – and that’s why edge seals are so crucial.
NREL scientist Michael Kempe exposes edge seals to different configurations and environments using Atlas Weather-Ometers.
On what looks like a whirling see-through geodesic dome – albeit just two feet in diameter – NREL scientists attach matchbook-sized samples that simulate the construction of PV modules to determine at what combination of UV radiation, high temperature, high humidity, and mechanical stress those samples can fail.
It’s important that manufacturers not just check for single stresses. By demonstrating that a combination of two or three factors can cause a failure, NREL is helping manufacturers prepare for the worst.
“We help manufacturers to know what kind of stress to put on their samples to determine if Sample A is better than Sample B,” Kempe said. “Every tiny detail, every aspect of these things has to be examined.”
A typical 12-millimeter-wide edge seal should keep out moisture anywhere in the world – from Salt Lake City to Bangkok – if it maintains a good adhesion, Kempe said. And the cost is between $1 and $2 a module, whether it is a tape-style edge seal or a hot-melt extrusion.
For humidity tests, NREL uses a vacuum oven to expose samples to controlled relative humidity using saturated salt solutions: lithium chloride for low humidity; magnesium chloride for 25% to 31% humidity; sodium nitrates for higher humidity.
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