Some circuits draw the current from 20mA to 50mA (0.05A) only. You can a Zener diode voltage regulator circuit. The Zener diode keeps a fixed voltage, 5V. It needs a resistor to limit the current to it and loa.
[pdf] While denoted as 12 volts, these panels typically function at a higher output voltage level, generally between 17 to 22 volts in peak sunlight. The variance in voltage output arises from several factors, including panel type, environmental conditions, and the inherent properties of solar cells.
[pdf] This reference design has a maximum output power of 215 Watts and ensures maximum power point tracking for PV panel voltages between 20V to 45V DC. High efficiency was achieved by implementing a novel interleaved active-clamp flyback topology with Zero Voltage Switching (ZVS).
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