MPPT vs PWM: Which Charge Controller is better to use?

PWM is short for Pulse Width Modulation. The PWM controller is in essence a switch that connects a solar array to a battery. It technically modulate the width of pulse under certain rules, thus change the voltage and frequency of output energy from the solar panel to charge the battery. The result is that the voltage of the array will be pulled down to near that of the battery.

MPPT is short for Maximum Power Point Tracking .

The MPPT solar controller always detects the solar panel output voltage and current in real-time and continuously track the maximum power (P=U*I), regulates the output voltage correspondingly so that the system can maximize the power to charge the battery.

PWM solar controller charges the battery with constant 3 stage Charging (bulk, float and absorb), while the MPPT controller is Maximum power point tracking and can be thought of as multi Stage charging. Thus, the conversion efficiency of MPPT controller is relatively 30% higher than that of PWM.

PWM solar controller charges the battery with constant 3 stage Charging (bulk, float and absorb), while the MPPT controller is Maximum power point tracking and can be thought of as multi Stage charging. Thus, the conversion efficiency of MPPT controller is relatively 30% higher than that of PWM.

• Bulk Charging: This stage is mostly the PV system proceeds to charge the solar battery. When the battery voltage is low, the system will charge the battery with high current and voltage. There is a maintenance point (overcharge protection) of the PWM solar controller, when the voltage at the battery end is higher than this maintenance value during charging, the direct charging will stop
• Absorb Charging: After first stage bulk charging, the battery normally will wait for a period  to allow the voltage to fall naturally, and then it enters the balanced charging stage. the stage also can be called as the "constant voltage charging".
• Float Charging: This is the last stage of PWM 's 3 stages charging. we call it "Trickle charging", at this stage, PWM controller charge the battery at a low rate and constant current. Most rechargeable batteries will have self-discharge, which make it lose power after being fully charged . If the charging current continues same small rate as that of self-discharge , the charge power can be maintained.

Compared to PWM Solar Controller's 3 stage charging, MPPT solar charge controller has 4 stages.

• Bulk Charging: unlike PWM controller, whose output is at a constant value at the bulk charge stage, MPPT controller will adjust the output voltage to charge the battery, ensure to maximize the power from PV array.  When the sunlight is strong, the output power of photovoltaic cells increases greatly, and the charging current can soon reach the threshold, abort the MPPT charging and switch to the constant-current charging method. When the sunshine is weak, cannot maintain the constant charging current, it will turn to the MPPT charging mode, until the battery vol
• Balance Charge / Boost Charge: As the battery is charged to the boost voltage setpoint, the solar controller continuously adjusts the charging current to keep the battery charging process.
• Absorb Charge: at the absorb charge stage, as the battery voltage increased, the charging current gradually decreases, when the charging current falls to about 0.01C, the constant voltage charging ended.
• Float Charge:  The main purpose of this charging stage is to compensate battery's self-discharge power. at the process, the battery gets fully charged.