As the name suggests, a solar charge controller is a component of a solar panel system that controls the charging of a battery pack. The solar charge controller ensures that the battery is charged at the right rate and at the right level. Without a charge controller, the battery can be damaged by incoming power and may also leak back into the solar panel when the sun is not shining.
The job of a solar charge controller is simple, but it's important to understand the two main types, how they work, and how to pair them with solar panels and batteries. Armed with this knowledge, you're one step closer to building an off-grid solar system!
How does a solar charge controller work?
A word of caution before we begin: we're going to talk about voltage, amperage, and wattage.
The solar charge controller is connected between the solar panel and the battery to ensure that the electricity from the panel reaches the battery safely and efficiently. The battery is fed into an inverter, which converts direct current into alternating current to run the device (aka "load").
The four main functions of the solar charge controller are:
- Receives input power from solar panels
- Control the amount of power sent to the battery
- Monitor battery voltage to prevent overcharge
- Allow electricity to flow only from the solar panels to the batteries
When a battery is charged, its voltage increases until it reaches a limit. If the additional charge exceeds this limit, the battery may be damaged. Therefore, a battery's ability to provide or receive electricity can be measured by its voltage. For example, a typical 12-volt AGM lead-acid battery has a voltage of 11.8 volts at 10% charge and 12.9 volts at 100% charge.
The main function of the solar charge controller is to ensure that the amount of power sent to the battery is enough to charge it, but not too much, so as not to raise the battery voltage above a safe level. It works by reading the battery's voltage and calculating how much extra energy is needed to fully charge the battery.
Another important function of the charge controller is to prevent the current from returning to the solar panel. When there is no sunlight, the solar panel does not produce any voltage. Because the current flows from the high voltage to the low voltage, if nothing stops, the energy in the battery will flow into the solar panel. This can cause potential damage. The charge controller has a diode that allows electricity to flow in one direction, preventing current from feeding back into the panel.