[E. Pluribus Unum]

Coal-fueled power plants work most efficiently running flat-out. This is a way to store the energy they produce during off-peak hours and distributing it during peak hours.

Any storage mechanism is going to lose energy in the process.

[Brookhaven]

If you read the fine print in the story, you realize what they really have created is a scam.

They fill the resivoir at night, paying for electricity at the lower off-peak rate. The empty the resivor during the day, creating electricity, and selling it back to the power company at higher peak rates.

The entire process is a net energy negative, but it creates a profit.

Of course, if the power company wasn’t forced by govt. regulations to purchase the electricity from third parties, the entire enterprise would collapse.

[Donald Rumsfeld Fan]

Any storage mechanism is going to lose energy in the process.

That's not a problem. Energy storage is key. That's why hydroelectric is the only renewable that makes any sense were energy is stored in reservoirs behind dams. Or pumping water to a sufficient height and storing it as potential energy. The higher you can pump it the more energy available.