There are two methods for loading a solar charge controller from a solar panel: the MPPT and the PWM Solar Controller. These technologies are both good options when it comes to effectively charging your battery.
What needs to be determined when choosing between PWM and MPPT solar charge controller is which best suits your system.
To understand the difference between these two solar charge controllers, let's take a look at the typical power curve of a PV panel (Figure 1). This is important because it shows the expected power output based on the combined voltage and current generated by the photovoltaic panel. The ideal ratio of current to voltage to produce the most power is MPPT. This changes depending on the irradiation conditions during the day.
Figure 1: Power curve of a PV panel
MPPT vs PWM
PWM Charge Controller
PWM is the abbreviation for Pulse-Width Modulation. While charging, the solar charge controller lets in as much current as the PV panel can generate in order to reach the target voltage. When the battery reaches its target voltage, the controller will then switch between the battery and the dashboard, which regulates the battery voltage and makes it constant. This fast switching method is called PWM, it ensures that your battery is charged by preventing it from overcharging.
Figure 2: PWM charge controller
Figure 3: Power curve of a PWM Controller
MPPT Charge Controller
MPPT (Maximum Power Point Tracking) provides an indirect connection between the battery and the PV generator. This indirect connection includes a DC/DC voltage converter which takes the additional PV voltage and transforms it into an additional current at a lower voltage without necessarily losing power.
Figure 4: MPPT charge controller
Figure 5: Power curve of a PV panel with load ranges for MPPT controllers.
MPPT controllers are able to achieve this through an adaptive algorithm, which adjusts the input voltage to maintain the most efficient level of power for the system in place.
How to Choose The Right Charge Controller
When choosing the right charge controller for you, there are several factors to consider. These include site conditions, grid size and load, system components, and the cost of your solar power system.
Temperature
For colder conditions, an MPPT controller would be the smarter choice for you. In fact, the more the operating temperature of the solar module decreases, the more the Vmp increases. With the MPPT controller, you can capture the excess voltage from the solar module in order to charge your batteries. This makes the MPPT controller 20-25% more efficient than the PWM controller in colder conditions.
The PWM solar charge controller, on the other hand, would not be able to sense the surge because the battery charges to the same voltage as the pulse width modulation technology. However, when these panels are placed in places where the temperature is warmer, their Vmp decreases and the peak power point operates at a voltage closer to that of a 12V battery. As long as there is no surge to transfer in this case, the utility of the MPPT will become useless. This negates the advantage that MPPT enjoys over PWM.
Grid to load
Relationship between network and load ratio If the solar panel is larger than the energy drawn from the batteries by the load, the batteries will likely stay near a full charge level. In this case, a PWM controller would be able to effectively maintain the system without the added cost of an MPPT controller.
System size
PWM controllers are best suited for small power systems for three reasons. First of all, the PWM controller works with constant harvesting efficiency, regardless of the size of the network. Second, an MPPT controller is less efficient in low power applications. Finally, PWM is less expensive than MPPT controller, making it the more economical choice for customers.
Type of solar module
Independent off-grid solar modules are typically 36 cellular modules that are compatible with both PWM and MPPT technologies. Other grid-connected solar modules available today are not 36-cell modules, making them incompatible with off-grid power systems. An example of this would be a 60 cell 250W panel. This value is too low for a 24 Volt battery, and too high for a 12 Volt battery. With MPPT technology, you can track the MPPT of these less expensive grid tie modules while charging the battery. The PWM regulator does not have this function.
Cost
The MPPT controllers are more expensive than the controllers PWM. However, the advantage of using MPPT is that it is more effective under specific conditions. If you want to buy an MPPT, it is better to first check whether the specialized function of the MPPT can be applied to the site conditions. If you find out that the functions of MPPT are not applicable in your chosen site, it would be more economical for you to choose the PWM controller.
In conclusion, before choosing the controller for you, it would be better to check the site, its conditions, the functions you would need and your budget for the technology. To make it easier for you to choose the type of charge regulator you need, here is a summary of the comparison between the PWM solar charge controller and the MPPT solar charge controller. Make sure you take the factors presented above into consideration before purchasing your charge controller!