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.

Traditional Solar Inverters perform MPPT for an entire array as a whole. In such systems the same current, dictated by the inverter, flows though all panels in the string. But because different panels have different IV curves, i.e. different MPPs (due to manufacturing tolerance, partial shading, etc.) this architecture means some panels will be performing below their MPP, resulting in the loss of energy.^[1]

A new approach offered by a number of companies employs panel-embedded electronics, which enables tracking the MPP of each panel individually. This approach ensures that each panel will perform at its own peak power point, independently of the other panels which may require different current due to uneven shading, soiling or electrical mismatch. Some of these solutions make use of Power Optimizers, a DC to DC converter technology developed to maximize the energy harvest from solar photovoltaic systems.

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.

[edit] References and further reading

General references

• "T.Bazouni: Easymax Solar Energy MPPT (Solar Maximisers)". http://solarfreaks.com/viewtopic.php?f=5&t=2. Retrieved 2007-04-11. 
• "T.Bazouni: Solar Panel I/V curves (Extracting maximum power)". http://solarfreaks.com. Retrieved 2007-05-11. 

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