And, while yes, the prices tend to spike into negativity for short periods, that's actually pretty normal to happen for countries which partake in the Synchronous grid of Continental Europe then and now.

The base issue, or at least a bigger part of that then wind/solar is, of that is actually coal. A coal plant needs tens of hours, up to days to shut-down; and then another few days to start up again - and such starts-stops are quite taxing on the plant; it can only survive a dozen of those before requiring major maintenance to happen.

Wind can actually be turned off quite dynamically (rotate the blade such that the angle of attack for the wind goes down to zero), not milliseconds, but a few seconds to minutes.

For the reverse you need storage, things like batteries or hydro (pumped storage) can and are used for that already.

Using terms like "Exportweltmeister" (export champion) in context of the European energy market is just rather non-sense, Germans energy politic is far from perfect, but it was never trimmed for export.