Charge Controllers PWM vs. MPPT

If you find yourself needing to replace the battery in your solar system within 3 to 5 years of installation, it’s likely that there was a fault in the system. This fault is often caused by overcharging or discharging, which can lead to significant damage. To prevent such issues, it’s crucial to incorporate a charge controller into your solar system circuitry. This controller can be added as a separate component or integrated as part of the circuit that connects to the solar panels.

What does a charge controller do?

A charge controller simply regulates the amount of electric current added or drawn from electric batteries, to protect against electrical overload, overcharging, and over voltage. One of the biggest problems with batteries is their limited ability to be recharged multiple times or deeply discharged. A charge controller tackles this issue by regulating the voltage and current of the battery, ensuring it stays in check.

In solar systems, charge controllers may limit overcharging and discharging by either of the following methods:

1. Disabling the current flow into batteries when they are full
2. Diverting excess electricity to an auxiliary shunt load like an electric water heater when the batteries are full
3. Disengaging from charging a battery when it exceeds a set high voltage level, or re-enable charging when the battery voltage drops back below that level.

Some charge controllers also monitor battery temperatures to prevent overheating while others transfer data to remote displays or even have displays of their own with data logs to keep track of electric flow over time.

There are 2 major types of charge controllers:

Pulse Width Modulation (PWM): This type of controller operates by sending out a series of short charging pulses to the battery. It decides how often it sends out the charges and how long each one should be, based on the current state of charge of the battery. Short and few pulses are sent out for a battery that is fully charged, while Long and consistent charges are sent out for a discharged battery. PWM charge controllers are affordable and suitable for small off-grid solar systems, such as 12V setups. However, they come with several disadvantages. First, they can cause interference with radio and TV equipment due to the sharp pulses, they generate while charging the battery. Additionally, PWM controllers reduce the solar panel voltage to match the battery voltage, which leads to energy loss, particularly when using 24V solar panels with 12V batteries. In this scenario, the controller wastes a significant portion of the solar-generated electricity by lowering the voltage to match the battery. Unlike MPPT controllers, PWM controllers lack a step-down feature, meaning they can’t efficiently convert higher voltage to lower voltage, further exacerbating energy loss. To minimize inefficiency, the battery voltage should match the solar panel’s output, but even then, the system may not fully harness the solar array’s potential.

Maximum Power Point Tracker (MPPT): MPPT charge controllers are a vital component of solar energy systems that can greatly improve efficiency and energy output. Unlike traditional charge controllers, MPPT controllers are designed to maximize the power generated by solar panels by matching their output voltage to the battery’s input voltage. This ensures that the charging process is as efficient as possible, even when using higher-voltage panels with lower-voltage batteries. One of the key advantages of MPPT controllers is their ability to allow for the connection of higher-voltage panels to lower-voltage batteries without losing power. This is achieved by adjusting both the voltage and current to maintain the same power output, thus minimizing energy wastage. In contrast, non-MPPT controllers can result in significant power loss when handling mismatched voltages. Some of the key benefits of MPPT controllers include maximizing energy output by operating solar panels at their most efficient point, allowing the use of multiple panels in series to reduce wire size and costs, minimizing power loss over long wire runs and in varying weather conditions, and being suitable for extreme temperatures, low sunlight, or low battery charge. While MPPT controllers may be more expensive than traditional PWM controllers, they only add around 2% to system losses, compared to the significant losses incurred by non-MPPT systems when dealing with mismatched voltages. Therefore, the investment in an MPPT controller can lead to substantial long-term energy savings and improved overall system efficiency.

The Right Choice of Controller for You

Making the “correct” charge controller choice does not mean choosing between PWM and MPPT charge controller technologies; rather, it means determining which kind would work best for your solar system. In addition to avoiding creating a system that will not work well, the goal is to save money by not purchasing an expensive item that you do not really need. When choosing a solar charge controller, it’s important to consider the system voltage, solar array current, and battery type. The decision between PWM and MPPT controller’s hinges on achieving the right balance between power optimization and battery lifespan.

PWM controllers are a cost-effective option suitable for small systems, particularly in warmer climates. However, they can lead to significant power loss when coupled with high-voltage panels, often found in mobile setups such as RVs. On the other hand, MPPT controllers offer greater efficiency, especially when the solar panel voltage exceeds the battery voltage. These controllers boost current to the battery, reducing power loss. It is crucial to match the solar panel’s voltage to the battery voltage when using a PWM controller to prevent power loss. For superior efficiency and long-term savings, especially in larger systems, investing in an MPPT controller is the wiser choice.

Summarily, Charge controllers help avoid situations that could endanger safety and shorten the lifespan or performance of batteries. By including a charge controller, you can effectively manage the charging and discharging of the batteries, extending their lifespan and ensuring the overall health and efficiency of your solar power system.