Comparison of methods
Both perturb and observe, and incremental conductance, are examples of "hill climbing" methods that can find the local maximum of the power curve for the operating condition of the array, and so provide a true maximum power point.[8][11]
The perturb and observe method can produce oscillations of power output around the maximum power point even under steady state illumination.
The incremental conductance method has the advantage over the perturb and observe method that it can determine the maximum power point without oscillating around this value.[6] It can perform maximum power point tracking under rapidly varying irradiation conditions with higher accuracy than the perturb and observe method.[6]However, the incremental conductance method can produce oscillations and can perform erratically under rapidly changing atmospheric conditions. The computational time is increased due to slowing down of the sampling frequency resulting from the higher complexity of the algorithm compared to the P&O method.[12]
In the constant voltage ratio (or "open voltage") method, the current from the photovoltaic array must be set to zero momentarily to measure the open circuit voltage and then afterwards set to a predetermined percentage of the measured voltage, usually around 76%.[12] Energy may be wasted during the time the current is set to zero.[12]The approximation of 76% as the MPP/VOC ratio is not necessarily accurate though.[12] Although simple and low-cost to implement, the interruptions reduce array efficiency and do not ensure finding the actual maximum power point. However, efficiencies of some systems may reach above 95%.[16]