Some links here, MOV only
Surge arrestors are used on AC and DC side of PV inverters for protection, to clamp high voltage transients. One inverter I have (actually several) are in the SMA family SUNNY BOY 5000-US / 6000-US / 7000-US / 8000-US. These come with a kit of MOV to protect the DC side: The MOVs are about...
diysolarforum.com
MOV with thermal over-current protetion
Surge arrestors are used on AC and DC side of PV inverters for protection, to clamp high voltage transients. One inverter I have (actually several) are in the SMA family SUNNY BOY 5000-US / 6000-US / 7000-US / 8000-US. These come with a kit of MOV to protect the DC side: The MOVs are about...
diysolarforum.com
That one now shows large quantity only, but check their site for others.
I figured observed brightness change meant moderate over-voltage, likely not an issue.
If it doesn't show up as brighter, might be a brief high spike more likely to damage electronics.
Would rather see scope trace to know what's happening.