PWM controllers are best suited for smaller solar systems with a solar panel voltage closely matching the battery voltage. However, they are less efficient than MPPT controllers, especially when the solar panel voltage is significantly higher than the battery voltage. Read my expert article on the best PWM solar charge controllers.
Thus, in case of a solar array of a higher voltage (by using a 24V panel or by connecting two 12V solar panels in series), the solar charge controller is a must. Here are listed the main functions of the charge controller in a solar panels system: – Taking care that the battery bank is not getting overcharged during the day.
This gadget regulates the power flow between the solar panel and the battery, ensuring that the battery remains at a consistent state of charge. Since solar panels produce different amounts of electricity depending on factors such as weather conditions, the charge controller ensures that excess power doesn't damage the batteries.
There isn't any 'excess' - the controller only uses what it needs/can use to supply charging energy. If it can use all your panel's output it does, if it can't it doesn't. Similar to your solar panels sitting there in the sun not connected to anything.
If you have a 36V solar panel and a 12V battery, 2/3 of the voltage gets wasted because the PWM controller doesn’t reduce the voltage. Read my article about the PWM charge controller efficiency. With a PWM charge controller, you must closely match the solar panel voltage to the battery bank voltage.
There are two kinds of solar charge controllers. PWM does simple pulse width modulation to limit intake voltage (E.g. 18V) to that appropriate for battery charging (e.g. 14V). The only thing it considers is correct battery voltage. MPPT controllers also "scan" the panel dynamically, varying their current draw to seek maximum watts.