It's a sign of a grid stability issue. A power grid needs to balance input, output and losses. An imbalance in either direction is bad.

A negative price means the grid is worried about a collapse. They are willing to pay sinks to come online NOW, or for production to go offline.

The solution isn't less renewables however! It's more storage, and better smarts on the grid. Most grids are poorly designed for renewables, and their loads characteristics. That needs to change rapidly.