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Advanced Design Concepts

Panel Characteristics

• The output from PV panels varies with conditions:

  • Sunlight intensity varies, PV panels have relatively constant voltage and proportionally-varying current. Naturally, output power (the product of the current and voltage) increases as solar intensity increases.
  • As the panels' temperature increases, the output voltage decreases; consequently output power decreases with temperature.
    

• Output power thus varies with the resistance of the load, and has a maximum (known as the maximum power point).

• As the maximum power point varies with temperature and illumination, the inverter's Maximum Power Point Tracker (MPPT) continually adjusts its resistance in order to gain the most power from the solar array.

• Panels are rated in terms of the maximum voltage under open circuit (Voc) and maximum current under short circuit (Isc) conditions, and the current and voltage at the maximum power point (Impp, Vmpp). When designing, care should be taken that maximum voltages and currents of panels and inverters are not exceeded in low and high temperatures.