In terms of its basic form, solar photovoltaic power generation is a very simple proposition. Hang the solar panel on the DC load and it will run until the sun goes down. Connect the solar panels to the grid-connected inverters, as long as the sun is shining, it will supply power to the utility. Everything is very easy-until the sun no longer shines.
What is becoming more and more complex is energy storage for use when the sun is not glowing or the grid is not working. To store electrical energy to complete useful work in the future, the battery needs to be connected to the solar photovoltaic system. After adding the battery, the charge controller will become one of the most important system components.
PMW Solar Charge Controller
A PWM solar charge controller stands for “Pulse Width Modulation”. These operate by making a connection directly from the solar array to the battery bank. During bulk charging, when there is a continuous connection from the array to the battery bank, the array output voltage is ‘pulled down’ to the battery voltage. As the battery charges, the voltage of the battery rises, so the voltage output of the solar panel rises as well, using more of the solar power as it charges. As a result, you need to make sure you match the nominal voltage of the solar array with the voltage of the battery bank. *Note that when we refer to a 12V solar panel, that means a panel that is designed to work with a 12V battery. The actual voltage of a 12V solar panel, when connected to a load, is close to 18 Vmp (Volts at maximum power). This is because a higher voltage source is required to charge a battery. If the battery and solar panel both started at the same voltage, the battery would not charge.
A 12V solar panel can charge a 12V battery. A 24V solar panel or solar array (two 12V panels wired in series) is needed for a 24V battery bank, and 48V array is needed for 48V bank. If you try to charge a 12V battery with a 24V solar panel, you will be throwing over half of the panel’s power away. If you try to charge a 24V battery bank with a 12V solar panel, you will be throwing away 100% of the panel’s potential, and may actually drain the battery as well.
MPPT Solar Charge Controller
MPPT solar controller stands for "Maximum Power Point Tracking". It will measure the Vmp voltage of the panel and down-convert the PV voltage to battery voltage. Since the power going into the charge controller is equal to the power output from the charge controller, when the voltage is lowered to match the battery pack, the current will rise, so you will use more power available on the panel. You can use a solar array with a higher voltage than the battery, such as the easier-to-obtain 60-unit nominal 20V grid-connected solar panel. Using 20V solar panels, you can charge a 12V battery pack, or two in series can charge a 24V battery pack, and three in series can charge a 48V battery pack. This opened up a variety of solar panels, which can now be used in off-grid solar systems.
The solar controller is responsible for managing the power from the solar array into the battery pack. This ensures that the deep-cycle battery will not be overcharged during the day, and will not flow energy back to the solar panel overnight and drain the battery. Some charge controllers have other functions, such as lighting and load control, but managing power is their main job.