In addition to its status as a carbon-free energy source that can provide baseload electricity, hydropower also offers a window into a future where variable renewables — such as wind and solar — can be more widely integrated into the grid.

Pumped-storage technology holds energy in the form of water in a reservoir that is moved up from a lower basin. The water is released through turbines from the higher elevation when electricity demand is greatest, and excess energy moves the water back up to refill the upper reservoir — usually overnight or on the weekends when demand is low, according to the National Hydropower Association.

The promise of pumped storage has found a fan in Senate Energy and Natural Resources Chairman Ron Wyden.

“I have long thought that storage and storage technologies is an area where we have gotten short shrift,” the Oregon Democrat said Monday at the NHA’s annual conference.

Wyden has criticized the Energy Department’s proposed fiscal 2014 budget, which suggested a “singularly unwise” 22 percent cut to energy storage programs. He called the proposed reduction a shortsighted move that hampers the future of a clean-energy economy.

More than 20 gigawatts of pumped-storage capacity is in use domestically, the hydropower association says, and developers have proposed adding 31 gigawatts to supplement the growing amount of clean-yet-intermittent resources being deployed out West. A February 2013 study by the Electric Power Research Institute called pumped storage the “most likely form of large new hydro asset expansions” in the United States.

But as with any capital-intensive clean-energy project requiring long lead times, pumped storage has run into a dearth of favorable tax policies that could spur even more growth. Lawmakers have proposed expanding investment tax credits and clean-energy bonds for developers to no avail.

“The reality is, efficient energy storage is the key to unlocking the full potential of intermittent renewable such as wind and solar,” Wyden said.