Local researchers concerned about fragile solar cells
The jagged white line is a crack in a sample of a solar cells polycrystalline silicon wafer formed along the boundary of the crystal grains. Tests at Lehighton Electronics, Inc. uncovered micro-cracks in samples that could lead to failures of solar arrays over time.
"With so many people investing in energy conservation," said Austin Blew, "I want to be sure that there are enough precautions and tests being done that failures in the installation over time, don't occur."
Blew is president of Lehighton Electronics, Inc., a 40-year-old Carbon County-based manufacturer of instruments used to qualify solid state materials. In association with an industrial standards organization, LEI had been analyzing samples of polycrystalline silicon, a lower cost material for making solar cells.
Peter George, LEI's electrical engineer in charge of performing the measurements on 10 six-inch square wafers, was startled when he noticed that one of the wafers had cracked. After discussing the occurrence with Blew, they arranged to review their tests, handling procedures, and to view all the samples under a high-power microscope.
Silicon wafers used in electronics have traditionally been grown from a single crystal, an expensive process that results in a uniform surface on which to build the electronic circuitry. With the explosive growth in the demand for low-cost solar energy panels, manufacturers have begun offering an alternative silicon wafer, one formed of many crystals-called polycrystalline.
To the unaided eye, the polycrystalline silicon looks very much like the galvanized zinc coating on steel, with one polygon-shaped crystal grain butting against another.
In going over his testing, George noticed that in the sample that failed, his tests had measured a high resistance to the flow of current at the exact location where the sample later cracked. He believes he had discovered a micro-crack in the wafer and that it occurred at the boundary where the crystal grain met.
"Out of the 10 samples, four broke somewhere on the wafer," Blew noted. "We have been testing materials from much smaller size to 12-inch wafers and we have never seen this type of breakage."
As competition continues to heat up in the solar power industry and polycrystalline silicon continues to proliferate, Blew wonders if there will be significant product failures much sooner than the projected 20-to-25 year life expectancy.
Although solar cells have no moving parts, they are subject to heating and cooling, and in some applications move during the day to follow the sun for maximum efficiency. If the solar cells contain small cracks, over time, Blew believes the thermal and mechanical stresses could cause failure.
He is particularly concerned about these types of possible scenarios since a major solar park is planned in Nesquehoning. Although he is concerned, Blew is not familiar with the type of solar cells, the source of supply of the solar panels, or the quality assurance on the solar cells for that project.
"We discussed a proposal for LEI to guide in choosing, receiving inspection, and pretesting," said Blew.
Typically, 20 to 24 solar cells are connected to produce a solar panel. Depending on its location, a crack in a single solar cell could affect the panel anywhere from reducing performance to causing a failure of the panel.
Blew feels that if, over time, cracks should become a widespread problem in polycrystalline silicon photovoltaic cells, it could lead to a wave of product failures, warranty claims, and ultimately supplier failures.
Blew recognizes that LEI's testing was limited to only 10 samples (estimated value $15,000 each) and that he has no knowledge of where they came from or if they were production or prototype samples. Therefore, they may not be typical of solar cell wafers in the marketplace.
Yet, never having previously seen micro-cracks in silicon wafers, Blew has been sending word to the industry to check further into this potential problem.
As a sidenote, after 40 years as owner of Lehighton Electronics, Inc., Blew is in the process of retiring and has put the business up for sale. He hopes to find a buyer that will continue to operate the high tech business at its current location.