It doesn’t start with poor installation, but that seems to be at least part of the problem. Hackaday – Solar System Wars: Walmart Versus Tesla.
So some of the details of Walmart’s suit against Tesla for the solar-panel-related fires has come to light. Some of it is what I expected, and some of it isn’t.
After Walmart had 3 solar-related fires in a short time they had Solar City/Tesla “de-energize” all remaining systems. (Disconnect from the inverter/mains as far as I can tell.) But that didn’t stop one more fire from breaking out in a de-energized panel assembly.
Among the problems that Walmart’s consultants discovered by investigating the surviving solar arrays were improper grounding, poor wire management leading to insulation abrasions and wear, and lack of as-built drawings and proper documentation. But the most glaring errors alleged by the inspectors were the presence of hotspots in the arrays, and improper installation of the connectors used to string together the solar panels.
Hotspots in photovoltaic arrays occur when one or more cells in a series-connected string of cells are underperforming for some reason — say, by being shaded by leaves or dirt. The shaded cell or cells can then become the current limiting element in the series circuit, which can lead to reverse-biasing of the bad cells. This essentially dumps all the power from the good cells into the bad cells, heating them up to possibly the point of failure due to melted solder joints, cracked silicon, and, as appears to be the case with the Walmart fires, ignition of the materials used to encapsulate the cells.
These are much larger installations than any I’ve ever dealt with. I had 2 largish panels on my boat. Friends had 4 or 6, depending, but they sometimes were smaller. You can imagine that the roof of your average Walmart store would support quite a few panels, which will either give you more voltage, or more amperage, or some combination of both depending on how you wire them together.
There is a link to download the entire PDF of the suit at Hackaday. I haven’t done it. Yet.