At what point do we no longer need a diode in series with a solar panel to prevent discharge of a battery through the panel? Is it x amount of volts difference between peak power voltage and cell voltage? If so what's x?
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\$\begingroup\$ If (Vbatery>Vpv) and no diode then discharging. \$\endgroup\$– Marko BuršičCommented Nov 5, 2015 at 9:31
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1\$\begingroup\$ When it gets dark, the voltage of the solar panel drops. When it drops below the voltage of the battery, the battery will "try to charge" the solar panel which of course is useless and must be prevented. When it's dark, solar cell voltage is 0 (zero) so you ALWAYS need a diode. \$\endgroup\$– BimpelrekkieCommented Nov 5, 2015 at 9:31
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\$\begingroup\$ Would the dark leakage of the panel thats traditionaly blocked with a silicone diode get lower as V batt is reduced? would a low Volt battery on a high volt cell be OK with no diode? How far away from mppt would this be ? enough to make the simple Si diode actually more efficient despite its volt drop ? \$\endgroup\$– AutisticCommented Nov 5, 2015 at 10:30
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1 Answer
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If the voltage of the two power sources (the panel and the battery) are different, then you'll need, at least, one diode to prevent the current from the battery through the panel.
If your batteries are NOT rechargeable, I'd also put another diode to prevent the opposite situation of the panel voltage being greater than the battery voltage, what would cause it from being "charged", which is not allowed in a non rechargeable battery.
simulate this circuit – Schematic created using CircuitLab
