PWM versus MPPT solar charging | Difference between PWM and MPPT solar charge controller

This page compares PWM versus MPPT solar charging and mentions difference between PWM and MPPT solar charge controllers.

Introduction: Solar charge controller functions similar to regular battery charger as it regulates flow of current to the battary from solar panel. There are two types of charge controllers which can be used between solar panel output and battery input. They are PWM charge controller and MPPT charge controller. Both of these methods are used to charge the battery from solar panel.

The main functions of these charge controllers are as follows.
• It prevents battery from over charging.
• It prevents battery from deep discharge.

What is PWM solar charging ?

PWM stands for Pulse Width Modulation or Pulse Duration Modulation. It functions as electronic switch. In this method average value of voltage (or current) fed to load is controlled by a switch. It turns ON and OFF between supply and load based on battery charging status.

During normal charging period, PWM controller delivers as much current as required from Solar PV panel to the battery. When battery reaches target voltage, PWM charge controller disconnects battery from PV panel to prevent it from over-charging.

Voltage output from PWM generator can be calculated as per following equation.
Vout = Vmax * Duty cycle (%)
Where, Duty Cycle (%) = [ TON/(TON+TOFF) ]*100
Here, TON + TOFF = period of the pulse width modulated waveform which is equal to 1/Frequency.

PWM charge controller operates close to maximum power point but often slightly above it. PWM controllers are available at cheaper rate and in smaller sizes. The low pass filters (usually RC type) are used to convert the PWM output to desired DC voltage. Due to less electronic components in its design, PWM controller has longer lifespan. All the latest microcontrollers are available with PWM feature which makes it easy to develop PWM solar charge controller.

Solar Electricity Block Diagram
Figure : Solar Electricity

What is MPPT solar charging ?

The optimal ratio of Current (I) to Voltage (V) in the power curve of a PV panel to generate most power is known aa MPPT i.e. Maximum Power Point. MPPT curve varies based on irradiation conditions.

MPPT offers indirect connection between PV panel and battery. It functions as DC to DC voltage converter. It is suitable when battery voltage is less than the PV panel array output. MPPT utilizes extra PV voltage of solar array to generate extra current at low voltage without loss of power. This increases efficiency of the solar system.

DC to DC converter are of two types buck converter and boost converter depending upon output voltage is greater or less than the input voltage. When output voltage is less than the input voltage buck converter configuration is used. Refer Buck Boost converter >> for more information.

Difference between PWM and MPPT solar charge controller

Following table mentions difference between PWM and MPPT solar charge controller types.

Parameters PWM solar charge controller MPPT solar charge controller
Full Form Pulse Width Modulated Maximum Power Point Tracking
Function As electronic switch between solar panel and battery As smart DC to DC converter between solar panel and battery
Efficiency Less efficient More efficient
Optimization It can not optimize for voltage differences. There is no load optimization. It can optimize for voltage differences. There is DC load optimization.
Capacity (Amp) Less More
Output Less More
Price Less More, 2 to 3 times of PWM controller
Lifespan Longer due to few electronic components and less thermal stress Shorter due to more electronic components and more thermal stress
Size Smaller Larger
Warranty Less More
Application For smaller systems, For solar panels with max. voltage of up to 18 V which can be used to charge 12 V battery. For larger systems and when solar array voltage output is substantially greater than battery voltage.

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