Solar photovoltaic panels achieve rated power in clear sun at sea level and 68 degrees F. They produce less power when they heat up, and they produce more than rated power when they are colder than 68 degrees. The documentation that comes with new panels warns installers of this, in most cases, wire bundles and charge controllers must be upgraded when installed in areas where the temperature goes below freezing regularly.
Our array is rated at 32 amps, but in the winter I have frequently seen it produce almost 40 amps on clear days. The reason for this is the that silicon has very high temperature conductivity coefficients, which is what slows computer chips and solar panels down when they get hot. Solar panels in Phoenix in the summertime generally only produce about 70% of their rated power. At Antarctic weather stations they can produce almost twice their rated power.
The type of battery you’re charging may have it’s own impact on the charging rate due to temperature as well, depends on the battery chemistry, but your panels most certainly lose power as they heat. Take care, Rudydoo