Currently there does not exist a commercial viable pumped hydro installation in the world that buy overcapacity renewable energy and later sells it at a profit. There are a few experimental and proof of concept installations that demonstrate the possibility of hydro as a battery, and at least one operate as an additional reservoir to a hydro dam, but the commercial viability of buying cheap renewable energy to pump water in order to generate electricity later when the price is high is not yet here.

Demand management is also a great idea in concept but the commercial viability is questionable as long as people can just turn on the cheap gas burners. Commercially, turning off production and keep the industry closed when renewable are not producing is much more expensive compared to just paying what ever price society currently demands when burning fossil fuels.

Remove fossil fuels from being viable choice in the energy grid and the economic viability would change dramatically for every other energy source, including hydro pumps and nuclear. Demand management might even become a possible strategy to a point where it can have an significant impact on the energy grid. For now most grids operates by combining cheap renewable with cheap fossil fuels, with the environment taking the real cost when the fossil fuels burns.