Hi,

The optimum resistance depends on the rated Current and Voltage from the PV Panel. A higher voltage and corresponding lower current (which would occur with a panel of comparable total area) both require a higher resistance value.

The PV panels are made from phototiodes connected in series, but the graph in post #2 shows just one diode. The curved lines show the I/V characteristic at various light levels. The diagonal "load lines" correspond to different resistance values and the requirement is that the I/V lines should cross them at proportional distances from the origin (0). That occurs with a vertical load line (short-circuit), but the corresponding voltages are all zero, so that's not a useful measurement.

The top I/V curve begins to fall at about 300 mV (R = 0.3 volts / 1.3 amps = 0.25 ohm), so a load with a resistance less than that is essential. Note how "bad" is the lineararity (proportionality) where the curves cross the horizontal axis (open circuit load).

A "5 volt" panel, for example, may have about 12 "diodes" in series and for the same current as in the graph would be rated at perhaps 6 watts. For such a panel, a resistance of around 12 * 0.25 (=3) ohms might be acceptable, but a lower value would be preferred.

Cheers, Alan.

The optimum resistance depends on the rated Current and Voltage from the PV Panel. A higher voltage and corresponding lower current (which would occur with a panel of comparable total area) both require a higher resistance value.

The PV panels are made from phototiodes connected in series, but the graph in post #2 shows just one diode. The curved lines show the I/V characteristic at various light levels. The diagonal "load lines" correspond to different resistance values and the requirement is that the I/V lines should cross them at proportional distances from the origin (0). That occurs with a vertical load line (short-circuit), but the corresponding voltages are all zero, so that's not a useful measurement.

The top I/V curve begins to fall at about 300 mV (R = 0.3 volts / 1.3 amps = 0.25 ohm), so a load with a resistance less than that is essential. Note how "bad" is the lineararity (proportionality) where the curves cross the horizontal axis (open circuit load).

A "5 volt" panel, for example, may have about 12 "diodes" in series and for the same current as in the graph would be rated at perhaps 6 watts. For such a panel, a resistance of around 12 * 0.25 (=3) ohms might be acceptable, but a lower value would be preferred.

Cheers, Alan.