When considering the use of solar panels for battery charging, you may have encountered the terms MPPT and PWM. MPPT stands for maximum power point tracker, while PWM refers to pulse width modulation.

This article aims to discuss the distinctions MPPT VS PWM charge controller, as well as provide insights on which one is a better choice.

What are the Differences Between MPPT and PWM

Both MPPT and PWM technologies serve the purpose of safeguarding your battery against potential charging-related damages. In fact, incorporating either an MPPT or PWM charge controller is crucial in your solar setup.

MPPT Solar Charge Controller

The MPPT solar charge controller is designed to maximize the power output of the solar panels by tracking the maximum power point (MPP) of the panels. It adjusts the input voltage and current to ensure that the solar panels operate at their maximum efficiency, regardless of changes in environmental conditions such as temperature or shading. In other words, it extracts the maximum amount of power from the solar panels and converts it into the optimum charging current for the battery.

Pros of MPPT

One major advantage of using an MPPT charge controller is the improved efficiency of your solar system. With an MPPT controller, you can experience up to 30% more charging current, leading to higher overall efficiency for your system. This increase in charging current can significantly enhance the output of your solar panels.

Additionally, MPPT charge controllers are particularly efficient in overcast conditions. Since solar panels already generate less electricity on cloudy days, it is crucial to maximize their efficiency. With an MPPT controller, you can ensure that any potential hindrances to efficiency are minimized, allowing your system to make the most of available sunlight even on cloudy days.

Cons of MPPT

The price of MPPT is more expensive.

MPPT charge controllers tend to have larger physical dimensions, which can pose challenges during installation if there are space limitations in the work area.

PWM Solar Charge Controller

Unlike MPPT charge controllers, PWM (Pulse Width Modulation) charge controllers work by simply regulating the charging voltage and current flowing from the solar panels to the battery. They are known for their simplicity and cost-effectiveness.

Pros of PWM

One major advantage of PWM charge controllers is their affordability. They are generally less expensive compared to MPPT controllers, which makes them a popular choice for smaller solar systems or those with budget constraints.
Additionally, PWM controllers are typically smaller in size compared to MPPT controllers, making them easier to install, especially in situations where space is limited.

Cons of PWM

PWM charge controllers do not track the maximum power point of the solar panels. This means that the efficiency of the system is not optimized in changing environmental conditions. PWM controllers simply reduce the charging voltage of the solar panels to match the battery's voltage, which can result in lower overall system efficiency.
PWM controllers are less efficient in extracting power from the solar panels, particularly in situations with shading or partial panel blockage. This can lead to reduced charging current and lower energy production.

MPPT VS. PWM

MPPT VS. PWM: Comparison in Appearance

Both MPPT and PWM charge controllers have similar appearances with electrical connectors for battery and solar panel connections. They also include LED lights for monitoring. However, MPPT controllers are typically larger and heavier due to the presence of DC-to-DC converter coils, while PWM controllers are compact and lightweight.

MPPT VS. PWM: Comparison in Working Principle

MPPT charge controllers employ advanced technology to efficiently convert high-voltage power to low-voltage power using a DC-to-DC converter. These controllers continuously monitor the solar array's maximum power point and adjust the voltage and current accordingly using the P = V x I equation. This ensures that the batteries receive the maximum power available from the solar panels.

On the other hand, PWM charge controllers operate by acting as a switch that directly connects the solar panels to the batteries. They utilize predetermined intervals to open and close the switch for charging the battery. When the switch is closed, the voltage of the PV array is forced to match the battery voltage, resulting in a reduced power output.

During the bulk charge mode, the switch remains ON to recharge the battery. To maintain the battery voltage at the absorption voltage, the switch is rhythmically opened and closed as required. Once the absorption is complete and the battery voltage reaches the float voltage, the switch is turned off. Similarly, to maintain the battery voltage at the float voltage, the switch is intermittently opened and closed.

MPPT vs. PWM: Temperature Differences

As the sun shines on solar panels, they tend to get hotter. In warmer temperatures, the voltage at open-circuit and maximum power point decreases while the current remains constant.

In this regard, MPPT controllers have an advantage over PWM controllers. MPPT controllers can extract more power from a solar array under colder temperatures compared to PWM controllers. At standard testing conditions (25°C), the operating voltage at the maximum power point is around 20V, while the battery voltage is about 13.5V. In chilly temperatures, MPPT controllers can generate up to 20-25% more power than PWM controllers.

PWM controllers, on the other hand, are unable to adjust both the voltage and current. Their pulse width modulation technology limits them to the low battery voltage and corresponding current on the I-V curve.

MPPT vs. PWM: Panel Shading

Under normal conditions, a solar array operates with evenly distributed solar radiation across its surface, resulting in one maximum power point (MPP) on the P-V curve. However, shading from trees, clouds, or other objects can block some sunlight, creating multiple MPPs. MPPT controllers have the capability to track and set the highest MPP as the operational point, effectively dealing with partial shading. PWM controllers, on the other hand, are unable to handle this scenario due to their fundamental operation.

MPPT vs. PWM: PV or Battery Voltage Differences

For both types of charge controllers, the PV voltage must be higher than the battery voltage for efficient charging. MPPT charge controllers can effectively operate with varying PV and battery voltage differences. For example, an MPPT controller can effectively charge a 12V battery with a 36V solar array.

On the other hand, PWM charge controllers perform best when the PV voltage is close to the battery voltage. Multiple PWM controllers are ideal for a 12V solar array and 12V battery configuration. However, PWM controllers become less effective when there is a significant difference between the PV and battery voltage.

MPPT vs. PWM: Series vs. Parallel Connections

Series and parallel wiring configurations have different advantages depending on the situation. MPPT controllers generally allow for more series connections, making it suitable when panels are exposed to varying lighting conditions. MPPT controllers typically have higher PV voltage limits (e.g., 100 volts) compared to PWM controllers. For example, with an MPPT controller, you can series-connect up to four 12V 100W solar panels without exceeding the PV voltage limits.

In contrast, PWM controllers often require parallel connections when connecting multiple solar panels. This is because many PWM controllers have low PV voltage constraints (e.g., 25V or 50V), limiting them to one or two 12V solar panels connected in series.

MPPT vs. PWM: Cost Considerations

When it comes to charge controllers, the cost factor can greatly influence your decision-making process. PWM (Pulse Width Modulation) charge controllers are readily available at affordable prices, with online options ranging from $15 to $25. However, it's important to exercise caution when purchasing one at such low prices, as quality may be compromised.

For those seeking better performance and reliability, investing in a higher-priced PWM charge controller is advisable. These typically start around $40 to $50, offering improved features and durability. Remember, paying a bit more upfront can result in long-term benefits and peace of mind.

Alternatively, MPPT (Maximum Power Point Tracking) charge controllers are renowned for their advanced capabilities. The price range for MPPT charge controllers varies significantly, starting from $80 and going up to $500, depending on voltage and current (A) ratings. It's essential to consider your specific requirements and budget before making a selection. LiTime provides best-budget high quality 30A and 60A MPPT with the price only within $300. 

Shading Tolerance: MPPT controllers are more tolerant to shading or partial obstructions on the solar array. They can handle shading on specific panels or parts of the array without affecting the overall system performance significantly. PWM controllers, on the other hand, are more sensitive to shading and can experience a drop in power output if any part of the array is shaded.

System Scalability: MPPT controllers are suitable for larger solar power systems that require more energy. They can handle higher power levels, making them a better choice when you need to scale up your system and increase energy generation.

Despite of these advantages, there’s one more thing that needs to consider. If you plan on adding more equipment to your system in the future, it would be wise to consider the potential increase in power needs. If your system is already close to the maximum capacity of a PWM controller, the addition of new appliances could overload the system. In that case, upgrading to an MPPT controller with its higher power handling capacity would be necessary to ensure the system can meet the increased demand. It's important to plan for future expansion and choose a charge controller that can handle the anticipated power requirements.

FAQs about MPPT VS PWM

1.What is the main difference between MPPT and PWM charge controllers?

The main difference is in how they regulate the charging process. MPPT controllers track the maximum power point of the solar array to extract the most power, while PWM controllers simply regulate the voltage to the battery.

2.Which one is more efficient, MPPT or PWM?

MPPT controllers are generally more efficient than PWM controllers. They can extract more power from the solar array, especially in colder temperatures or when the array experiences shading.

3.Can an MPPT be too big?

There is a practical limit though, if the solar array is too large then the power is just wasted, since the charge controller is always limiting the output. A typical recommendation is to limit the solar array to 110%-125% of the maximum controller rating.

4.What size charge controller do I need for a 300W solar panel?

A 30A controller is adequate for a 300 watt solar panel set up. Read on Choosing the Right Size of Solar Charge Controller for more information.

5.Will an MPPT over charge a battery?

When the battery voltage reaches a point where the battery charger decides that the battery is full, the charger will cut out, and stop drawing power from the MPPT controller. In other words, the battery charger will present a high impedance to the MPPT controller.

6.What does an MPPT controller do when the battery is full?

 When the battery voltage reaches a point where the battery charger decides that the battery is full, the charger will cut out, and stop drawing power from the MPPT controller. In other words, the battery charger will present a high impedance to the MPPT controller.

7.Can I connect an MPPT directly to inverter?

No! MPPT solar charge controllers help to flow the current efficiently into your depleted battery. If we connect an MPPT solar charge controller directly to the inverter, your soalr system can get damaged, but if not damaged, there will be zero input in the inverter. So connecting MPPTs directly to the inverter is a bad idea!

8.How many amps do I need for MPPT?

You take the total watts of the solar array divided by the voltage of the battery bank. That will give you the output current of the soalr charge controller. For example, a 1000W solar array ÷ 24V battery bank = 41.6A. The rating of the charge controller should be at least 40A.

Final Thoughts

In summary, it is important to carefully consider the needs and conditions of your solar system, as well as your budget, when choosing a solar charge controller. This comparison between MPPT and PWM charge controllers can help you make an informed decision. Ensure that you evaluate the factors mentioned above before making a purchase. LiTime offers tech-driven best value solar charge controllers suitable for both 12V and 24V systems, with a 30A option, as well as controllers for 24V, 36V, and 48V systems with a 60A capacity. Enjoy your solar system with LiTime.