So, when the sun is shining and the wind is blowing and the price is negative, savvy operators of battery storage, pumped hydro, etc. stock up on energy for later.
Then, when it's the middle of the night and the wind's not blowing, the price spikes, and those who stored energy ahead of time make a profit providing that energy when it's needed most.
Of course this is an abstraction, and I'm not an expert, but... are there utilities whose rate structure enables execution of this kind of arbitrage business model?