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MPPT Vs. PWM Solar Charge Controllers: Which Is Right For Off-Grid Homes?

Aug 1, 2022


If you’re considering an off-grid home powered by renewable energy, “MPPT” is a term you’re likely to encounter.

MPPT stands for maximum power point tracking, and an MPPT charge controller can be a critical part of ensuring your solar panels and a battery bank can work well together. Let’s explore what you need to know about charge controllers and whether an MPPT or a Pulse Width Modulation (PWM) solar charge controller is best for your photovoltaic (PV) system.

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What Is A Solar Charge Controller?

An off-grid solar-powered home needs a battery backup system and a solar charge controller – also known as a solar regulator – to ensure safe, reliable battery charging.

Solar modules typically produce direct current (DC) power at a voltage that’s different from the voltage most batteries – whether they’re lithium ion or lead acid – require to charge.

Also, the voltage of a solar cell’s power output varies by the intensity of the sunlight and the temperature.

A solar charge controller is a DC-DC converter that allows the solar panels’ voltage to better match the battery voltage requirements. It constantly monitors the output voltage, determines the peak power and adjusts the voltage to provide the right amount of input voltage to the battery. 

Can You Charge Solar Batteries Without A Charge Controller?

Charging backup batteries from a solar array without a charge controller could damage the batteries if your home is off-grid. Without the charge controller, batteries can overcharge and discharge when not in use. The controller will ensure your battery system is at the correct state of charge.

Hybrid solar power systems, which are grid-tied and equipped with backup batteries, don’t usually need a charge controller. When a hybrid system’s battery is fully charged, power goes into the utility grid, not into the battery.

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At A Glance: What Is An MPPT Solar Charge Controller?

MPPT solar charge controllers are the newest technology for matching voltage. They’re up to 30% more efficient than the PWM controllers that preceded them. This efficiency comes from constantly monitoring the output voltage throughout the day and determining the maximum voltage possible for the temperature and amount of sunlight. Your installer should recommend whether you need an MPPT or PWM charge controller for your specific installation.

Charge controllers of the MPPT variety can also work with lower-cost solar panels designed to be compatible with grid-tied systems, potentially offering substantial savings for large solar arrays.

Thanks to MPPT, off-grid systems are more productive on cloudy days when the system’s maximum power point will fluctuate.

The MPPT is more expensive, though, and loses its efficiency advantage in smaller systems, so that’s why this technology is most often used for commercial and utility-scale solar installations, as well as off-grid homes with systems larger than 170 watts.

Is The MPPT Solar Charge Controller The Best Choice For Homeowners?

While the MPPT solar charge controller is most efficient for large-scale PV arrays, homeowners with solar panel systems smaller than 170 watts may find PWM charge controllers to be more cost-effective for their needs.      

Both types of charge controllers generally include safety features that can sense short circuits, high current draw or undercharged batteries. These features will often automatically take action to prevent damage to the PV modules, inverter and other solar power system components.

Installations with MPPT controllers may allow systems to run at a higher voltage level than the batteries, possibly resulting in more power for immediate use. A PWM controller drops the panel voltage to match the battery voltage, which results in less power.

Other Considerations When Choosing A Solar Charge Controller

System size might be the biggest factor in choosing between an MPPT and PWM controller. But a few other points, including the ones noted below, are also worth considering.

Cold climates: Off-grid homes in cooler climates can take advantage of the fact that MPPT charge controllers work better in lower temperatures.

Panel type: The typical off-grid solar panel uses 36-cells and is designed to charge a 12-volt battery. Grid-tied PV arrays usually use 60- and 72-cell panels that operate at a higher voltage.

Your budget: If you’re trying to go for the lowest possible cost, a PWM controller offers the cheapest way to add a solar charge controller to your solar power system. A PWM can be as little as a third of the price of a comparable MPPT controller.

The Bottom Line: Solar MPPT Is Often A Good Choice

Off-grid homes come in many sizes. If yours is a tiny home, a PWM controller might be sufficient. A full-sized, off-grid home is likely to get improved results from an MPPT controller. Talk to your installer about whether going off the grid makes the most sense for you, and what additional equipment you’ll need to keep your home running smoothly.

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