Just to add to that: Any fluctuation in prices works to incentivise storage, negative prices are not so special in that regard.

Negative prices allow for some weird actions to become profitable - like starting an empty washing machine, turning in the light in an empty room or needlessly heating some water tank. Basically everything we are used to think of as waste. It sounds absurd, but it's not really a big deal.

And even better, the incentive to expand the grid. The market is easy to control, because the money flows via the internet. But how to transport the energy?

Without a proper grid not possible. The various countries block the expansion for political reasons. They would loose their power.