What is Maximum Power Point Tracking?

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How maximum power point tracking (MPPT) calculations workThe technology in Maximum Power Point Tracking , or MPPT, is quite new in the renewable energy market but can be found in grid-tie inverters and charge controllers from several manufacturers. MPPT charge controllers offer series charge control features as described in our other articles. However, they beat standard controllers because they can also improve the renewable energy source's overall efficiency and power output dramatically, giving more energy savings with the same equipment.

This MPPT's function may be slightly difficult to understand but it's definitely worth trying. As with other electrical devices, the PV module output is the product of the rated current and rated voltage under a load, giving the module's rated power.

A normal power curve of a PV panel is illustrated in the graph. The x-axis is the module's output voltage; the y-axis is the output current. The point illustrated on the graph is the VOC position (Voltage Open Circuit) which indicates zero current flowing with no work done, like when charging the batteries.

With a load connected to the panel, the current flow rises with voltage dropping slowly as the power curve path progresses.

The highest point on the curve reflects its highest efficiency; this is the maximum power point (MPP). But battery voltage alone will probably not identify this efficiency point due to its variable nature, which means that the probability of the PV output hitting the MPP is not very high. The result is lost power and efficiency (equal to the difference between battery voltage and MPP multiplied by current).

The MPPT controller "sweeps" the PV panel's power curve (or the output of any other renewable source) to determine the maximum power point. The MPP also checks the battery or inverter load (in grid-connected systems) to determine the MPP for the electrical power level that is currently being produced. It sweeps the power curve periodically to make sure that the MPP is re-calculated regularly by the system.

Testing reveals that a MPPT system increases PV array wattage by an average of 15% through the year. PV arrays with 800W to the battery bank or grid will give 120W increase on average - that's the same as adding a free panel to your PV array.

Strictly PV systems should have an MPPT controller to supplement active tracking for an increase in daily energy generation.