MPPT vs PWM Solar Controllers

MPPT Controllers (Maximum Power Point Tracker) provide more power, especially in colder temperatures. They can also be used with less expensive 60-cell modules which are usually unsuitable for PWM Controllers (Pulse Width Modulation). Weighing these benefits versus the lower cost of a PWM controller will determine if an MPPT controller is right for your system.

While MPPT controllers cost more than PWM controllers, the following benefits often outweigh the extra cost:

• The additional power provided by the newer charging technology associated with MPPT controllers enables them to run larger electrical loads and help batteries maintain a higher state of charge which prolongs battery life. Since batteries typically cost several times more than charge controllers, the extra power that MPPTs provide is sometimes worth their higher price tag even before other benefits are considered. The amount of additional power an MPPT controller provides increases as temperature decreases. The extra boost provided by an MPPT is conservatively estimated to be 5-10% with 36 Cell modules, with larger gains from 60/72/120/144 Cell modules, but this boost can be much higher if temperatures are below room temperature for at least part of the day when the sun is shining.

• MPPT controllers can be used with less expensive 60/72/120/144 Cell modules that are usually not suitable for PWM controllers.  Large systems deploying MPPT controllers with multiple modules in series and parallel are often less expensive than similarly sized systems with PWM controllers and 72 cell nominal modules.

• MPPT controllers allow systems to support oversized PV arrays. Both MPPT and PWM controllers will be damaged if their Voc limits are exceeded by oversized PV arrays, but Victron, Enerdrive and Morningstar MPPT controllers can be connected to arrays that exceed their current ratings. The MPPT controllers are able to limit the current intake and avoid damage.  This is not the case with PWM controllers. Oftentimes it is advantageous to oversize arrays by 20% so that batteries can maintain a higher state of charge during several consecutive days of limited sunshine.