Key points of this article,Understand what MPPT and PWM are.Explore the main differences between MPPT and PWM.Understand what to pay attention to when designing MPPT and PWM circuits.

When there are different methods available to complete the same task, each method usually has its own advantages and disadvantages. But when carefully considering specific job requirements and resources, one of them usually stands out as a better choice.

The same applies to solar charging controllers. In this work, the two common choices are MPPT and PWM. In this article, shinetoo will discuss the differences between these two technologies, help you determine which one is more suitable, and provide design suggestions for using these two technologies.

What are MPPT and PWM?

MPPT (maximum power point tracking) and PWM (pulse width modulation) are both technologies that power solar charging controllers. PWM achieves this function by changing the duty cycle of the connection, charging the battery from the solar panel.

The function of PWM charging is like a switch, with one MOSFET used to bridge the connection between the solar panel and the battery. Usually, a microcontroller is used to change the duty cycle of the charging current to control the charging stage. Usually, PWM charging goes through three stages: forced charging, balanced charging, and floating charging.

The strong charging stage is when the charger allows a reasonable amount of current to pass through to charge the battery. The next stage is balanced charging, allowing the battery voltage to stabilize before releasing a constant current. Finally, in the floating stage, Trickle charging is ensured to compensate for the loss of battery self discharge.

The MPPT charger also goes through these stages when charging the battery. However, it adjusts the voltage and current at the same time to achieve this dynamically, so as to achieve maximum charging efficiency.

MPPT and PWM solar chargers

There are differences in various aspects between MPPT and PWM solar chargers.

1. Operation

The charging voltage and current generated by the MPPT charger are related to the maximum power on the I-V curve of the solar panel. The charging process also takes into account the temperature, angle, and exposure of the solar panel.

The behavior of a PWM charger is like a switch between a solar panel and a battery. It is not designed to track the maximum power on the I-V curve, so it will operate strictly under any circumstances.

2. Efficiency

The efficiency of MPPT chargers is much higher than that of PWM chargers. The efficiency of MPPT chargers can reach up to 99%, but the efficiency of PWM charging is only 50% -75%. Let’s explore why this situation occurs.

The behavior of a PWM charger is like a switch, so the solar panel will always be charged at the battery’s voltage. When a solar panel with an open circuit voltage of 24V is connected to a PWM charger, the voltage will be pulled down to almost the same level as the 12V voltage of the battery. This reduces the charging efficiency by 50%.

On the other hand, MPPT adjusts the charging voltage and current to the maximum deliverable power. Its behavior is like a DC-DC transformer, rather than a switch, which allows it to minimize charging losses.

3. Cost

Due to its simpler structure, PWM chargers have lower costs than MPPT chargers. The cost of a PWM charger is usually less than $100, while the cost of an MPPT charger can reach hundreds of dollars.

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