Question

Why is my solar panel more efficient as the temperature increases, rather than less efficient?

Answer 1

Two conditions

1. Rating - Check the rating of the panel. If your operating temperature is less than the rating conditions (temperature), then it is likely the efficieny increases. Once you cross the rating  conditions the efficiency goes down.

2. Thermal solar panel - Here the panel is a hybrid one, a fluid is run through the panel to extract heat and keep the panel at rated condition. So the efficiency goes up.

Here is the graph of a silicon solar panel - Temperature vs efficiency