What is a solar charge controller?

A solar charge controller is a product for solar-powered voltage and current regulator. It is used in off-grid and hybrid off-grid applications to regulate power input from PV arrays to deliver optimal power output to run loads and charge batteries. So solar charge controller has been called solar charge regulators.

Reliable charging to maintain battery health and extend battery life is very important. The affected about how well, and how fast depend on the solar controller’s software controls and the electronic component hardware. Battery and PV voltage and current can change as second and the electron component in the controller must be able to respond fast enough to accommodate the changes.

You maybe have the best batteries and best modules just like PV array in the world, but they’re only as reliable as your solar controller. A poor solar controller maybe cause battery failure, even your entire solar system. Reliable in performance of the solar charge controllers extend battery life for many years beyond their normal life expectancy

The charge controller generally represents about 10% of your total off-grid power system costs, however batteries can be about 40% of the system cost and 80% of the system lifetime costs. So the small amount of money you might save deploying a cheaper charge controller will pale in comparison to the money and time wasted on battery replacement. You can use the best PV modules, batteries, wiring, and loads, but their capabilities will be restricted by the quality of the charge controller.

How does a solar charge controller work?

Off-grid Diagram with DC Load(how a solar charge controller is connected to power a direct current (DC) load)

When installing a solar charge controller, it is recommended that you connect and disconnect in the following order:

1. Battery to the controller
2. PV array to the controller
3. Electrical load to the controller

When disconnecting, you reverse that order. The battery provides power to the controller so always make sure that solar and loads are disconnected before connecting or disconnecting the battery from the controller. Connections between battery, load, PV array, and the controller should have disconnect switches to enhance safety and facilitate ease of installation and breakdown.

In the wire diagram schematic above with DC load, sunlight contacts the solar modules, which convert solar into DC electrical power that it delivers to a charge controller. The charge controller regulates the amperage and voltage that is delivered to the loads and any excess power is delivered to the battery system. So the batteries can keep their state of charge without getting overcharged.  Battery power is used to run the load when there is no sunlight.

Off-grid Diagram with AC Load(pertains to an alternating current (AC) load)

Note: the inverter is connected and powered from the battery, not the controller’s load terminals, like we did in the DC load example. That’s because the inverter can have a high energy surge upon start up, and this high current surge might be higher than the rated capacity of the solar charge controller, whereas the batteries will be able to meet the high energy surge requirement.

How many types of solar charge controllers?

The two major types of solar charge controllers as below:

1. Pulse Width Modulation (PWM) controllers
2. Maximum Power Point Tracking (MPPT) controllers

PWM controllers tend to be smaller and they operate at battery voltage, whereas MPPT controllers use a newer technology to operate at the maximum power voltage. This maximizes the amount of power being produced which becomes more significant in colder conditions when the array voltage gets increasingly higher than the battery voltage. MPPT controllers can also operate with much higher voltages and lower array currents which can mean fewer strings in parallel and smaller wire sizes since there is less voltage drop.

PWM controllers need to be used with arrays that are matched with the battery voltage which limits what modules can be used. There are many 60 cell modules with maximum power voltage (Vmp) equal to about 30V, which can be used with MPPT controllers, but are simply not suitable with PWM controllers.

Now answer the question: Which is better, PWM or MPPT? All things being equal, MPPT is a newer technology that harvests more energy. However, the advantages of MPPT over PWM controllers come at a cost, so sometimes a less expensive PWM controller can be the right choice, especially with smaller systems and in warm climates where the MPPT boost is not as significant.