U.S. Hydropower Fleet has Upside Power and Storage Potential

Photo: Danita Delimont / Getty Images

Hydropower has a dowdy, low tech image that conjures visions of concrete and degraded ecosystems. It is mostly shut out of the incentives driving solar, wind and other newer forms of renewable energy. InsideClimate News just dubbed it the “Unloved Renewable.” How wrong this image is according to a first-of-its-kind comprehensive study of the U.S. hydropower industry released by the Department of Energy’s Oak Ridge National Laboratory (ORNL) in Tennessee. 

ORNL researchers found that U.S. hydropower grew by 1.5 gigawatts to 79.6 GW over the past decade, thus holding on to its seven percent share of U.S. power supply. In so doing it is offsetting roughly 200 million metric tons of carbon emissions per year, equivalent to taking more than 42 million cars off the road.

Most growth has come through upgrading the capacity of existing hydropower plants, backed by $6 billion in investment over the past decade. And there is room for far more growth without adding any large dams. Energy blog Fierce Energy this week trumpeted the report’s finding that “an astonishing 77 GW of hydropower remains untapped.” 

Hydropower’s growth potential is a mix of further upgrades, smaller run-of-river projects that squeeze power from seasonally heavy water flows, and the addition of power generating equipment to some of the more than 80,000 non-powered dams in the U.S. (which currently focus exclusively on other services such as flood control, irrigation, and drinking water storage). Powering just the 100 largest of those dams would add 8 GW to U.S. hydropower capacity. 

Pumped hydropower plants, which store surplus power generation by lifting water to an upper reservoir, receive special treatment in ORNL’s report. The authors calculate that 21.6 GW of storage capacity in 42 existing pumped hydro plants “make up the overwhelming majority (97%) of utility-scale electricity storage in the United States.” 

And they see a major opportunity for adding pumped hydro as grid stabilizers to support growing levels of variable solar and wind power — especially as coal and nuclear power plants that historically helped regulate the grid shut down. 

Pumped storage is hydro’s high-tech play. Variable speed pumps driven by power-electronics have enhanced pumped hydro’s ability to provide grid services such as rapidly balancing supply and demand to regulate a grid’s AC frequency. Such advanced pumped hydro plants already operate in Asia and Europe. While none are yet are under construction yet in the U.S., the Federal Energy Regulatory Commission issued licenses for two last year; FERC is considering another 49 proposed projects with a combined capacity of 39 GW (see map below).

ORNL’s authors say pumped hydro currently struggles to compete in the U.S. given “current market structures” and the relatively low-cost of dispatchable natural gas power plants. But they note that FERC is testing a shortened 2-year licensing process for pumped hydro storage that could accelerate developments. 

Carbon regulations will help too. The Sacramento Municipal Utility District, which won one of last year’s FERC licenses for its 400-megawatt pumped hydro project, is betting that rising costs imposed by California’s carbon cap-and-trade program will ultimately tip the market against grid regulation with natural gas plants.

Coda: It is worth noting the positive interaction between hydropower and ‘better loved’ renewables such as wind power and solar power is bidirectional. While hydropower enables higher levels of the newer renewables, solar and wind also provide a backup for hydropower that is itself only as reliable as the rain and snowpack. 

The California Independent System Operator predicted earlier this month that the drought-stricken state will rely on its utility-scale solar power plants to make up for a dearth of hydropower. The state’s power grid manager estimated that hydropower output will drop to an “extreme” low of 4,628 megawatts during this summer’s peak season, down 43 percent from hydro’s 10-year average. 

In diversification lies security. 

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