This is an ideal diode board that uses a reverse biased MOSFET to pass current with losses much lower than any other kind of diode to prevent reverse polarity voltage discharge through a temporarily shaded solar panel in an array.

Ideal Diodes are also used in power ORing configurations, where multiple sources can be parallel wired and their output currents will be added together.

You can also use this pretty much anywhere you would use a normal diode but wish to consume less power and drop less voltage.