Depending on the size of the panel board and the exact source of the humidity, you could go for a simple heater, a de-humidifier, or even a proper air-conditioner. (A de-humidifier is a type of aircon.) In some of our outdoor panels, we put in a bar-heater as standard, with a thermal switch, so that in winter it is always on. In an emergency, a 60W or 100W light has served us well! (Unrelated - we've dried out an electric motor that was victim of a flood with a 500W halogen flood light for a few days - still working!)
Just be warned against just heating up the air in high-humidity situations, as apparently the warmer air absorbs more moisture. When the power fails and the environment is cold, the moisture then tends to condensate on the coldest object, usually metal. If the environment is polluted as well, then you tend to get tracking and even flash-overs. Humid sea air, cooling off and moisture then condensing onto 3kV rectifiers - kaboom! I've learnt a few expensive lessons! A de-humidifier solved the problem there very cost-effectively.
There are also other alternatives - Peltier effect coolers may be suitable for very small panels. I even heard of huge industrial panels cooled be a vortex-effect system that uses compressed air.
humidity
Re: humidity
