Depends on the type of plant: For "island or OFF-grid" systems, the question is superfluous, since this type of system always runs independently. For "ON-Grid" plants, batteries must be present, which not only bring the "sunshine" of the day into the night, but there must also be a converter electronics, which includes an "island network function". This is a special connection, "UPS" or "emergency power", often with limited power, through which certain consumers (e.g. refrigerators) can continue to be supplied in the event of a grid power failure.