Edit: According to the paper, it's economically viable when the output power price (post-pumping and running through the turbine again) can be > 2X the price of the hydropower, which with seasonal variation and spikey but 'free' sometimes power, could definitely help. Preferring something like solar over running a turbine could also help.
The challenge of course is that many times hydropower is nearly free and available in large quantities, as the dams are also used for flood control, so they either toss large quantities of water over the spillways (wasting it), or run it through a turbine - but they can't NOT move the water.
Edit: According to the paper, it's economically viable when the output power price (post-pumping and running through the turbine again) can be > 2X the price of the hydropower, which with seasonal variation and spikey but 'free' sometimes power, could definitely help. Preferring something like solar over running a turbine could also help.
The challenge of course is that many times hydropower is nearly free and available in large quantities, as the dams are also used for flood control, so they either toss large quantities of water over the spillways (wasting it), or run it through a turbine - but they can't NOT move the water.