Too Much Wind Energy? Save it Underground in Volcanic Rock Reservoirs

July 2, 2013 by  
Filed under Green Energy News

Gusting winds and swelling rivers bless the U.S. Pacific Northwest with an abundance of renewable energy resources in the spring and early summer. So much, in fact, that at times in recent years the Bonneville Power Administration (BPA), a federal utility, has forced wind farm owners to curb their output to keep electricity generation in balance with the rise and fall of demand on the grid. (See related quiz: “What You Don’t Know About Wind Energy.”)

Now a new solution for the region’s seasonal energy glut is on the table. Recent research from scientists at BPA and the U.S. Department of Energy’s Pacific Northwest National Laboratory suggests porous rocks deep in the Earth could store the wind’s intermittent power and make it possible to deploy renewable energy on command. (See related: “Global Renewable Energy On Track to Eclipse Natural Gas, Nuclear.”)

Too Much of a Good Thing?

This is much more than an academic exercise in a region that’s home to one of the largest networks of hydroelectric dams in the United States, a recent boom in wind installations, and state mandates for renewables on the grid. For wind farms, powering down turbines can mean giving up tax credits and millions of dollars in revenue.

BPA has said its hands are tied: It can’t spill more water over Columbia Basin dams without exceeding limits designed to protect salmon and steelhead, and it’s unable to send more electricity via existing transmission lines to buyers in California. Proponents of renewables, meanwhile, have called for scaling back generation from coal or nuclear plants before giving wind the boot. And the Federal Energy Regulatory Commission, or FERC, is requiring BPA to establish a better way to handle oversupply without discriminating against wind power.

Focusing on subterranean basalt reservoirs in eastern Washington State, the authors of this new study have examined the feasibility of deploying a system known as compressed air energy storage, or CAES. They analyzed geological data from petroleum exploration to identify a pair of sites where these volcanic rocks could store enough energy to power a total of about 85,000 homes per month.

 

A natural lava tube in California.

Photograph by Tim Laman, National Geographic

 

“We’re talking about air far below the water table, in the kinds of places where you would find things like fossil fuels,” said Haresh Kamath, energy storage program manager with the Electric Power Research Institute (EPRI). Natural gas and other fuels can and have been held in “similar rock formations for millions of years under pressure, and nobody notices anything at ground level,” he said. In a CAES plant, the underground reservoirs could provide the vessels where compressed air could be pumped and stored using surplus wind energy. During times of higher demand, such as hot summer afternoons, the air would be uncorked, heated, and used to turn a turbine to generate electricity.

Modern-Day Aeolus?

CAES has been in use at commercial scale at two sites for decades—in Germany since 1978 and in Alabama since 1991. (See related: “Frozen Fish Help Reel in Germany’s Wind Power.”) But these projects store air in tank-like salt caverns cleared out by solution mining. What’s different about the approach proposed for the northwestern United States is that the air would be stored in naturally porous and permeable volcanic rock. The idea echoes an ancient one. In Greek mythology, the gods kept blustery winds trapped in a hollowed-out mountain under the watchful eye of a jailer named Aeolus, who would unleash gales by stabbing his sword into the Earth.

Lacking the powers of a Greek demigod, modern-day CAES projects typically use natural gas to heat the air upon its release above ground, expanding its volume and velocity. But for one of the two proposed sites in Washington, in an area called Yakima Canyon, the researchers designed a new type of plant that incorporates geothermal energy instead. In addition to heating the air, geothermal energy in this new hybrid design would also power a chiller, which would cool the plant’s air compressors to make them run more efficiently. The other site, just north of Boardman, Oregon, near the Columbia River, is close to a natural gas pipeline and would lend itself to a conventional setup.

Researchers say these plants in the Northwest could switch between energy-storage and power-generation modes within minutes and make better use of the region’s abundant but intermittent wind power. ”It would be a relief to operators,” said Kamath. About 8,600 megawatts, or 13 percent, of the region’s power supply now comes from wind—equivalent to the output of about eight nuclear power plants-and it tends to pick up around the same time that late-spring snowmelt causes river flows and hydropower generation to swell.

But it is not only wind and water that this region has in spades. It also has enormous deposits of basalt stretched across thousands of square miles of a claw-shaped basin known as the Columbia Plateau Province. The recent research finds this basalt, most of which flowed from volcanic eruptions between about 17 million and 15 million years ago, could hold a key to taming the wind. (See related: “Mexico’s Robust Wind Energy Prospects Ruffle Nearby Villages.”)

Hidden Resources

This approach needn’t be limited to the Pacific Northwest. “There’s an awful lot of salt out there,” said Kamath. Northern Ireland, for example, has salt deposits where developer Gaelectric hopes to build a 268-megawatt CAES project in support of its growing wind capacity. And Germany’s RWE Power is working with partners to demonstrate a more efficient type of CAES plant using heat recovery and salt caverns in Stassfurt, northwest of the historic saltworks center in Halle.

But porous rock is far more common worldwide, Kamath said. “If you can use porous rock, you would be able to use [compressed air energy storage] in a much broader context.” In California’s San Joaquin Valley, the U.S. Department of Energy and state agencies have provided funds for utility PGE to test potentially suitable rock formations for CAES, including depleted gas reservoirs. The utility expects to complete analysis at three sites by 2015, and if all goes well, a 300-megawatt plant could enter commercial operation within eight years.

Work began as early as 2003 on a project studying porous rock reservoirs near Des Moines, Iowa, for CAES to capture off-peak wind production. The project involved nearly 100 municipal utilities, but ultimately failed after studies of the sandstone showed the geology would not support a project of the intended scale. In an interview, Steve Knudsen, who managed the latest study for BPA, expressed hope for renewed interest in the technology. One of the messages to take away from the study, he said, is “don’t give up yet.” (See related story: “Planting Wind Energy on Farms May Help Crops, Say Researchers.”)

Storage for a Changing Climate

Knudsen began mulling use of the Northwest’s porous rock aquifers for CAES after exploring the region for natural gas storage sites more than a decade ago. ”The higher the permeability, the faster you can inject and move the air into your underground storage formation,” he said. The conditions for relatively quick cycling (injection and withdrawal), however, were “too much of a good thing” for natural gas, which operators generally want to cycle only once a year, injecting gas during the summer and drawing it out in the winter. (See related: “Pictures: Flying Wind Turbines Reach for High-Altitude Power.”)

Compressed air at these sites could store the Northwest’s springtime energy surplus for as long as several months at a time. But the ability to store energy for even half a day can make a significant difference. In late May, BPA sold power at times for less than $1 per megawatt hour—”effectively giving it away,” Knudsen said. “We could have sold it for $35 if we could have saved it ’til the afternoon.”

Experts expect energy storage to become more important over time, as wind and solar generation bulks up in line with state requirements for clean energy. (See related: “Sizing Up Wind Energy: Bigger Means Greener, Study Says.”) “If we want to continue to integrate more and more carbon-free resources, we’re going to have to find ways to add capacity and flexibility,” said Joel Scruggs, a spokesman for BPA.

Climate change could also shift the seasonal dynamics. “In the Northwest, we have all this hydro, and if we have a drought we may not have as much water flowing down the river,” said Scruggs. Surplus wind energy captured at night and in the springtime in this scenario could become a vital resource for delivering power to homes and businesses. “With climate change, if we see dramatic shifts in the amount of rainfall and snowpack,” he said, “it’s just one more reason to store it and have it when we need it.” (See related: “Helix Collapse Fails to Crush Hope for Vertical Wind Turbines.”)

This story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge.

Comments are closed.