Why are sealants an important factor of quality in a panel?
Sealants are used to seal the junction box on the rear of the solar module to prevent moisture getting into connections and sometimes to bond the laminates solar panel into its aluminium frame. If poorly matched, some sealants can react with the plastics causing premature degradation. Although non-flammable sealants are available, cheaper, flammable alternatives are sometimes used to reduce costs.
Frame sealants need to stay flexible over time and in varying temperatures to allow for thermal expansion and contraction between the glass laminate and the aluminium frame.
When you are assessing a solar panel, look very closely for evidence that the sealants are applied precisely and carefully as a sign of good workmanship. Excess sealant oozing onto the glass indicates poor control over the dosage and could mean that too much is in some places, and too little in others.