Maximum-power-point tracking during outdoor ageing of solar cells

This paper describes how to select a passive load which would the most accurately follow the maximum-power-point (MPP) of small laboratory size solar cells installed outdoors in Central Europe. Either resistor or diode type of passive load have been used as a low-cost alternative to active MPP trackers (designed especially for a long-term outdoor stability study of different types of small size laboratory solar cells). The dye-sensitized solar cells have been chosen as a representative case since they exhibit similar current-voltage (I-V) characteristics dependence at different light intensities (G) and cell temperatures (TC) as other solar cell's technologies. The results showed that the most efficient tracking was achieved when the I-V characteristic of the optimal resistor or diode cross the MPP of the solar cell measured at G = 73 mW/cm2 and TC = 25 °C. A significantly better tracking could be obtained when instead of a resistor an optimal diode is used; the optimal diode consumes 96.5% of the annual energy that would be potentially produced by the solar cell connected to ideal MPP tracker while the optimal resistor consumes only 83.5% of that energy.