It depends on whether or not someone is able to demand delivery at that price and what other forces are in play. i.e. presumably there are regulatory requiremen

It depends on whether or not someone is able to demand delivery at that price and what other forces are in play. i.e. presumably there are regulatory requirements that some minimal amount of capacity must be available as generators typically can't quickly spin up based on the whims of the sun/wind... but what if the generator provides it and there are no takers which a zero/negative price would indicate? Of course that's not sustainable for long it becomes a persistent situation: at some point the generator must be subsidized, or can absorb a loss over brief periods for the 'privilege' of being a provider the rest of the time, or goes bankrupt. Running parts of businesses at a loss isn't unheard of provided the governments responsible for overseeing it are OK with and/or mandate it (a wide variety of services to rural customers here in the U.S. comes to mind) and the impacted business makes up for the loss elsewhere.