There are also technical and economic reasons this may not work beyond just inelastic vendor pricing, there is cost to transmission(loss) and all the step down that has to happen before electricity is at your door, that cost will be always positive so it may not actually be net positive.
At steep enough negative pricing this could be profitable, however at that point power plants with the highest costs and easiest scale down/ shut down procedures will start acting.
Projects like the one at Dinorwig (pumped hydro-storage) are more viable solution for excess capacity.
I think this is a little simplistic. Pumped hydro is very reliant on finding suitable geography which ultimately limits the potential capacity. I think it's more likely that grids of the future will rely on a variety of storage solutions (pumped hydro, consumer EVs, grid scale batteries etc.) and smarter load-shedding rather than any single solution being dominant.
https://scholar.google.co.uk/citations?view_op=view_citation...