As the solar panel is always made of waterproof materials, and uses a good sealant for its internal solar cells and wiring, there is no worry when we see rains drop on solar panels for long time, actually the solar panel is designed to work effectively when it is rained on for even decades. The damage which may be happened due to water is very rare, and if it occurred, you would be sure that the solar panel had a manufacturing defect from the beginning, and in this case, there is no worry as the supplier warranty will honor this, especially the warranty period for most of solar panel brands in the market is not less than 10 years.
The solar panel ingress protection indicates the protection level against environmental elements includes preventing water from entering inside the solar panel, and always be denoted by "IP" abbreviation. The number written after IP will indicate exactly what will the solar panel be protected against, and to what extent. For an instance, if we purchased a solar panel with IP65, then this means it has been well protected against dust and can withstand sprayed water at low pressure, but if we purchased a solar panel with IP67 or IP68, then it has been well protected against dust, moisture and it can be submerged temporary in water, so better protection, more reliability and longer life span.
The good quality solar panel manufacturer and supplier, not only protect you from being the solar panel damaged by water or not properly sealed, but also, they protect you from solar panel bad performance, we mean if it generates less output power that what it was designed and manufactured for. However, after a10 years of installing the solar panel, it will produce only 90% of its rated power capacity, and that is normal, it is an acceptable degradation in performance which you will notice it is already listed clearly in solar panel specification sheet.
Generally, although the solar panel manufacturer/supplier warranty period is so long, its real, and you will be able to replace the panel inside the warranty period limit free of charge, with no issue at all, because as said the manufacturer understand from the beginning that the solar panel will be installed outdoor, and it lifespan in 25 years or more.