MLE - Solar Panel Maximum Power Point Tracking (MPPT)

Photovoltaic (PV) panels are made up using several silicon junctions in series. When these junctions are illuminated and energised by light, a mechanism known as the photoelectric effect causes electrons to be displaced from the silicon, resulting in an electric current flow. Albert Einstein first explained this and consequently won the Nobel Prize for “his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect” in 1921.

The output from a PV panel depends on many factors including :-

• the amount of incident light energy received (a quantity known as insolation); for static panels this will vary throughout the day and as cloud cover changes;

• the area of the PV cell being illuminated – a proportion of the panel may be in shade from cloud or nearby structures for example;

• the electrical load attached to the panel.

Varying temperature also affects the cells, but to a lesser extent.

The maximum power is transferred from a solar panel when the impedance of the load it is driving is optimally matched to its source impedance. As you might expect, the panel’s source impedance also varies as the operating conditions change, and so more sophisticated systems use a Maximum Power Point Tracker (MPPT) to optimise the panel’s load conditions to its peak power transfer level. In operation the voltage generated at the PV panel terminals will vary as the MPPT automatically adjusts the power taken from the panel, maintaining that power at a maximum for the prevailing conditions.

It has also been shown that if a shadow falls across part of a PV panel, the silicon cells in the shade receive less light and their power output decreases. Under extreme conditions individual shaded cells may become reversed biased and produce hotspots in the panel unless precautions are taken. If shading conditions continue to vary such that the current peak power level is decreasing, it is quite common for a new peak power point to start to rise at a different point of the power/load graph. Some MPPTs using simplistic tracking algorithms get stuck tracking a local maximum in the power curve, and fail to change rapidly to the correct conditions [1].

Shading conditions will obviously vary on a minute-by-minute basis and so tracking the Maximum Power Point is a highly dynamic, complex situation. For best efficiency, an MPPT needs not only to track the current maximum power point but also be able to detect and change to a new, optimum operating point should it occur - all in real-time.

MLE have MPPT algorithms running on our own solar panels; real data from them is uploaded to our website periodically.

View the latest power output from MLE's solar panel

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MLE - Solar Panel Maximum Power Point Tracking (MPPT)