Maximum power point tracking

Of the maximum power point ( MPP or short ) is the point of the current-voltage diagram of a solar cell on which the largest power can be taken, that is the point at which the product of current and voltage is at its maximum. It is not constant but depends on the irradiation intensity, the temperature and the type of solar cells.

Definitions

The current-voltage diagram is typically applied such that the direction of current of the measured current is in the reverse direction of the solar cell. The current is thus positively applied in lighting, in contrast to the classical diode characteristic.

The ratio between the maximum power PMPP the solar cell at the maximum power point and the product of open circuit voltage ( VOC ) and short circuit current ( ISC) is called the fill factor FF:

A function of the incident radiation and temperature

With increasing irradiation power increases almost proportionally, the performance increases significantly. The voltage does not change much here. As the temperature increases, the voltage drops, so that the performance decreases ( Typical: -0.45 % / K for crystalline silicon cells), the current changes hardly.

Technical Solutions

Thus, a solar cell or a solar generator always operates at the MPP, usually regulated by a so-called MPP tracker (MPPT ) is the voltage to the required value. This purpose, the voltage is varied by a small amount. Increases or decreases in this case the product of current and voltage, ie, the power of the generator is maintained, the new voltage, otherwise the voltage is reset to its original value. This iterative process results from a microprocessor constantly, so even with changing irradiation conditions (factor > 10 between cloudy sky and sun) is always an operation at the maximum power point.

Partial shading of a solar cell strings leads to losses at the maximum extractable power, so MPP trackers are becoming increasingly integrated in each solar module.

• Photovoltaic