MPPT solar charge controller introduction video

A newer innovation in PV charge controllers is called maximum power point tracking (MPPT). Computer-driven circuitry in the controller scans both battery bank and PV array voltages at regular intervals, and calculates the optimum match between the array and battery bank. MPPT is able to trade volts for amps and vice versa (see the MPPT sidebar). Under some conditions, such as cold weather, overcast days, or low-horizon sunlight, energy gains of up to 35% are possible.

MPPT controllers have another big advantage of allowing higher-voltage PV arrays, which operate more efficiently and require smaller wire sizes from the array to the controller. In some cases, especially when the PV array must be located a long distance from the battery bank, the extra cost of MPPT is offset by the savings from being able to use smaller-gauge wire.

Beware of some caveats when choosing between MPPT and non-MPPT controllers. First, all the PV modules (or series strings of modules) feeding an MPPT controller should be identical. Mixing modules from different Ldsolars; using different PV technologies (monocrystalline, polycrystalline, or amorphous); or using modules with different voltages and different power ratings should be avoided, as MPPT gains can be compromised and mismatched modules could be damaged. 

Be careful when sizing series strings of PV modules that feed an MPPT controller. The “maximum open-circuit voltage” listed in the comparison table is just that—if you exceed this voltage, the controller can be permanently damaged. Remember that PV modules produce higher voltages in cold weather, so an array of three 45 V modules in series for 135 V might be just fine during the summer for an MPPT controller with a 150 V maximum rating—but could damage the controller when it is cold and sunny.

Extra caution is needed when designing and installing PV systems higher than 48 V. All combiner boxes and circuit breakers must be rated for the maximum system DC voltage, as DC electrical arcs are difficult to extinguish and can cause a fire. Accidental electrical shocks during installation that are merely unpleasant at less than 48 V can be lethal at higher voltages. Hire a professional if you have even the slightest doubt of your ability to install the system safely.