PWM vs MPPT Solar Charge Controller
What’s the difference between PWM and MPPT solar charge controllers?
Often a solar panel is attached to a battery as means for maintaining power during periods of no sun. Energy generated by the solar panels is stored in a battery, typically Gel technology. Gel is the recommended technology for this application as it has the ability to withstand the cyclic abuse.
The voltage output of the panel generally varies from the float voltage of the battery therefore a regulator or solar charge controller is required to ensure the battery is not overcharged and consequently damaged.
Therefore, the solar charge controller is a device used to control the charge coming in from a solar system to the batteries. They are essential in ensuring batteries are not overcharged. Overcharging a battery will significantly reduce the battery life and potentially cause damage beyond repair.
When a solar charge controller is used, the controller will take the power from a solar panel and regulate it to charge or maintain the battery in the most optimized way.
For example, a standard 12V operating voltage solar panel would have a nominal voltage of 18V. Connecting this directly to an AGM or Gel battery which is only charged at a max of 14.4-14.6V on boost charge will cause the battery to be overcharged unless a solar power controller is used.
What types of solar charge controllers are there?
There are two different methods used by the controller to regulate the power from the solar panel to charge the battery.
- Pulse Width Modulation (PWM)
- Maximum Power Point Tracking (MPPT)
PWM is the original method and has been around for many years while MPPT is the newer more efficient method. MPPT has been specifically designed to reduce the efficiency loss in charging batteries from solar panels.
How do PWM and MPPT solar charge controllers work?
A PWM controller clamps the solar panel output voltage to match that of the battery until its fully charged, then clamping it further to float charge the battery. The output from the controller is maxed at the solar panels output current The controller uses very simple algorithms to determine the correct voltage required for charging the batteries
MPPT controllers track the open circuit voltage of the solar panel and matches that with the peak current generated from the solar panel. The controller then tracks that as the maximum power point and converts that power to charge for the batteries. Using this maximum power point ensures that the panel is producing at its peak and the full wattage produced by the solar panel is being converted to charge for the batteries.
MPPT controllers have a greater input voltage range, allowing greater voltages in the cables from the panels to the solar charge controller. This again increases the efficiency of the system by reducing voltage loss in the cabling. All power generated by the solar panels is converted into charge for the batteries.
The Pros and Cons
Each type of controller has its own pros and cons.
The size, scope and budget of your solar system needs to be considered as a whole when deciding whether to use a PWM or an MPPT controller. But to make things easier, you can use the following table to weigh up the pros and cons of each controller type.
|PWM SOLAR CHARGE CONTROLLERS||MPPT SOLAR CHARGE CONTROLLERS|