It's economical to combine it with solar/wind on the grid. Both California and Hawaii are doing this right now. This form of energy is about 1/3 the cost per MWh of nuclear (as opposed to solar/wind alone which is about 1/6th the cost). It just hasnt been that cheap for very long.

Hydro as storage, better grid interconnects, demand shaping (e.g. using smart storage heaters that turn on when electricity is cheap) can bring down the cost still further.