Temperature
Many people believe hot and sunny summer days are prime solar energy producing conditions. However, cool weather can actually be better for solar panels, as most electronics do not fare very well in the heat. Heat actually reduces solar panel output, because of thermodynamics laws. Essentially, solar panels produce energy by absorbing photons of light to excite the electrons in a solar cell. This is how voltage is created. But, when it is hot out, solar panels are hotter, so more electrons are already excited. This means that photons can’t excite as many electrons, so less voltage is produced. So, the efficiency of the panels is reduced in the heat.
In general, solar panels are most efficient between 59 degrees and 95 degrees Fahrenheit. Keep in mind that this is the temperature of the physical panel, not the air temperature. Since panels are dark in color, they often heat up and are a few degrees hotter than the air temperature on a given day. So, the cooler fall temperatures can actually be great for solar panel efficiency!