Maximum power point tracker

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Solar cell I-V curves where a line intersects the knee of the curves where the maximum power point is located

A maximum power point tracker (or MPPT) is a high efficiency DC to DC converter which functions as an optimal electrical load for a photovoltaic (PV) cell, most commonly for a solar panel or array, and converts the power to a voltage or current level which is more suitable to whatever load the system is designed to drive.

PV cells have a single operating point where the values of the current (I) and Voltage (V) of the cell result in a maximum power output. These values correspond to a particular resistance, which is equal to V/I as specified by Ohm's Law. A PV cell has an exponential relationship between current and voltage, and the maximum power point (MPP) occurs at the knee of the curve, where the resistance is equal to the negative of the differential resistance (V/I = -dV/dI). Maximum power point trackers utilize some type of control circuit or logic to search for this point and thus to allow the converter circuit to extract the maximum power available from a cell.

Battery-less grid-tied PV inverters utilize MPPTs to extract the maximum power from a PV array, convert this to alternating current (AC) and sell excess energy back to the operators of the power grid.

Off-grid power systems also use MPPT charge controllers to extract the maximum power from a PV array. When the immediate power requirements for other devices plugged into the power system are less than the power currently available, the MPPT stores the "extra" energy -- energy that is not immediately consumed during the day -- in batteries. When other devices plugged into the power system require more power than is currently available from the PV array, the MPPT drains energy from those batteries in order to make up the lack. MPPT charge controllers are quickly becoming more affordable and are more common in use now than ever before.

The benefits of MPPT regulators are greatest during cold weather, on cloudy or hazy days or when the battery is deeply discharged. Solar MPPTs can also be used to drive motors directly from solar panels. The benefits seen are huge, especially if the motor load is continuously changing. This is due to the fact that the AC impedance across the motor is related to the motor's speed. The MPPT will switch the power to match the varying resistance.