It has a negative price precisely because at that given moment, nobody can use it for anything else.

Yes…. And capital costs to capture that ‘moment’ productively are likely not in favor, if this situation exists long term.

For example, Free power for an hour is useless if someone is running an aluminum refinery, because you can’t just start and stop it; and it costs so much capital to make that only operating 1 hour out of 24 is not economic.

And that is for a situation where electrical power costs are one of the most dominant costs!