alt Hacker NewsThe panels are designed to not provide current if no current is detected on the mains. Otherwise you would also have a live plug at the end of the panel. Killing your own customers is typically not a good business strategy, so quite a lot of safety has been focused on ensuring this isn't a problem.
Not just designed not to provide current, in general they simply can't. They follow the phase from the mains (the sine curve of voltage and current), without the mains there isn't a phase to follow and they simply can't output anything
This was a contributing factor in the Spain blackout, because even large-scale solar and wind plants were using the same type of simple inverters