Ironically, solar panel kits work best under cold and cloudy conditions than in the full sun. This is because temperature affects the efficiency of a solar panel. For example, a 100-watt solar panel at about 70°F temperature will become an 83-watt panel at 110°F. That being said, if your solar panels are regularly exposed to rainy or cold weather, a PWM controller’s input voltage ratings will pull down as the temperature drops. At high temperatures, the voltage input may drop to below the point needed to fully charge the battery. In such cases, an MPPT controller is the best option because it regulates temperature and compensates for the changing voltage. In fact, you can experience a 10-15% power gain in summer and a 20-45% gain in winter with an MPPT charge controller, although this may vary depending on a variety of different factors. Some solar controllers offer battery temperature sensors which will enhance the battery capacity. This is a great option for those looking to place their panels in varied environments with strong weather patterns.