> If there is excess power at zero marginal cost someone cunning is already planning on making some coin off it.

I'm not sure it's that simple as evidenced by the ever increasing hours of negative electricity prices.

As far as I know, there are so far no good applications for short bursts of negative prices. Everything that would love those is so capital intensive/high fix costs that even 10 or 20% utilisation rates at negative prices are not enough to make it economically viable.

Season excess is also a big problem. Batteries to smooth the days/nights cycles are fine, you can use them ~365 times a year. But a battery to smooth out summer/winter cycles can only be used once a year!