At the heart of every off-grid solar system is the charge controller. This is the part responsible for controlling the current and voltage that goes into the battery, preventing it from overcharging. Typically, 12V panels put out somewhere between 16V and 20V, so if there’s nothing to adjust the voltage going to the battery, the cells can get damaged. Most solar system batteries require around 14V to get charged. Solar charge controllers are available in a wide range of sizes, features and costs. They can range from 4.5A up to 80A. The three main types of solar charge controllers are simple 1- or 2-stage controllers, PWM (pulse width modulated) and MPPT (maximum power point tracking) controllers.
1- or 2- stage controllers feature shut transistors that control the voltage in one or two stages. They basically short the panel when a specific voltage is obtained. The main advantage is their unwavering quality, as they don’t feature a lot of parts, so there’s not much to go wrong. However. you’ll have a hard time finding such controllers, and they’re mostly considered out of date.
PWM controllers work by making a connection from the panels directly to the battery. They operate by pulling down the output voltage from the solar panels to match the voltage of the battery. As the battery charges, its voltage rises, so the output voltage of the solar panels rises as well, using more of the power. That being said, you need to ensure the nominal voltage of the panels matches the voltage of the battery. As briefly aforementioned, a 12V solar panel will actually release a load of close to 18 volts per minute. This is due to the fact that a 12V battery requires a higher voltage source to be charged.
And if you decide to buy MPPT solar charge controller, you can expect to pay more, but you’ll get the best performance. These charge controllers measure the voltage per minute of the panels and down-convert their voltage to the battery voltage. And due to the fact that the power that goes into these controllers is equal to the power that goes out of them when the voltage is dropped to match the battery’s voltage, the current is raised, so you’re using the power available from the solar panels more efficiently. These charge controllers allow you to use a higher voltage solar panel, such as a 60 cell nominal 20V solar panels that are readily available.
But no matter whether you buy MPPT solar charge controller, an PWM, or 1- or 2-stage model, their purpose is the same – to protect the solar battery from overcharging, thus increasing its lifetime and reducing system maintenance. Here’s how all of this is done.
The most basic function of the solar charge controller is to control the systems voltage and prevent charging by opening the circuit. Some charge controllers use a mechanical relay to open and close the circuit, stopping or starting power heading off to the battery. Most solar systems utilise 12V batteries, and solar panels transfer more voltage than necessary to charge those batteries. The charge voltage should be kept at optimum levels while the time needed to charge the battery completely is reduced. This allows solar systems to function optimally at all times. By running higher voltage in the wires from the panels to the controller, the power dissipation in the wires is also reduced completely. Furthermore, charge controllers also control the reverse power flow. These devices know when no power is coming from the panels, and they open the circuit to separate the panels from the battery and stop the reverse flow of current.
However, as briefly aforementioned, the solar charge controller can do more than controlling the voltage flow and prevent overcharging. For instance, if the battery is fully charged, the controller will provide an indicator on its display screen. Other useful information that solar controllers display include overloading, undercharging and deep discharge condition. A MOSFET can be used as a semiconductor switch by the charge controller to make sure the offload in low or overloading conditions is cut. The solar power is bypassed using a transistor to a dummy load when the battery is fully charged. All of this helps protect your solar batteries from overcharging.
That being said, the control of battery charging is a crucial part of your solar system. Most manufacturers of high-quality batteries specify the requirements for charging the batteries, temperature compensation, voltage regulations and low voltage disconnect in order to ensure you can get more use out of them. A quality charge controller won’t be too expensive in relation to the total cost of your solar power system, nor is it too complicated to understand why you need one. You can find a wide range of MPPT, PWM and 1- and 2- stage solar controllers online, so no matter what type of battery you have, you can rest assured you’ll find a suitable model.