[bert]

Here’s the explanation. The parameters are carefully considered to produce a net gain at less cost.

http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity

[dickmc]

The need for mitigation of wind fluctuations on grid operation via storage like pumped hydro is already becoming a serious grid reliability issue. This is already a serious concern on the ERCOT (Texas) grid system.

See Slide 118 for Generation Operation and 138 for Load Dispatching at http://www.ercot.com/meetings/ros/keydocs/2008/0227/ERCOT_final_pres_d1_w-o_backup.pdf