There are economic involved. Long term, it pays to have many variable load generation in the grid, because they are cheap and environment friendly. But a net n

There are economic involved. Long term, it pays to have many variable load generation in the grid, because they are cheap and environment friendly. But a net needs to be handled exactly to match supply to cost, and demand has a large random component that no-one foresee perfectly. Hence, negative prices are a normal feature of balancing demand and supply, which is a technical necessity not to have black-outs and brown-outs or, in this case, damage expensive base-load powerplants during emergency shut-downs.