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Wind turbines in Vantage, Washington.

These wind turbines whirring above the clouds in Vantage, Washington are just part of the Pacific Northwest's renewable energy boom. To manage a surplus of intermittent power, U.S. scientists propose underground compressed air storage in porous volcanic rock.

Photograph by Gordon King, Yakima Herald-Republic/AP

Josie Garthwaite

For National Geographic

Published July 1, 2013

Image of the 125 Anniversary logo 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.
This tunnel at California's Lava Beds National Monument is just one example of abundant volcanic rock formations that may be used to store surplus energy.

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 PG&E 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.

Joe Ratley
Joe Ratley

VERY thought provoking read, about off demand storage AND retrieval of electric wind energy generation. Several scenarios presented, some utilize natural gas for retrieval of wind energy in peak demand cycles. The fact that PG&E, aka "Pacific Gas & Electric" is involved raised a red flag for me. As "are these designs motivated to involve natural gas in wind energy storage during low demand AND wind energy retrieval during high demand". I'm not engineer, so I have only doubts & suspicions with them. Sounds to a layman as being overly complicated to involve natural gas in the electric energy prooduction AND  transmission processes. You be the judge. 

Jeremy Klapprott
Jeremy Klapprott 1 Like

Too much wind energy production in the Pacific Northwest? 

Washington = 2800 MW

Oregon = 3100 MW

Texas = 12,200 MW,  more than double capacity.  

Pfftt....Chicken feed...we do more than oil...

Alec Sevins
Alec Sevins

Based on the headline,  I was hoping this article would be about limiting the landscape-trashing proliferation of 400-foot "green" towers, but apparently that's a forbidden topic because anything that doesn't emit CO2 (after construction, that is) is sacred among techie "environmentalists."

Dave King
Dave King

@Alec Sevins :: Welcome to the 21st Century.  It's best to go ahead and move along with the rest of society unless you want to be stuck behind with the remaining bands of 20th Century troglodytes still clinging on to old ways because they seem to be 'best'.  The reality is that the cost of the negative externality of being a "landscape-trashing proliferation" (as you have referred to windmills) is much less than the cost of the negative externality of emitting CO2.  I hate to burst your bubble but just because you (personally) cannot see CO2 doesn't mean that it has no effects -- such an assumption would make you ignorant.  The entire matter has nothing to do with "techie environmentalists" and everything to do with being able to move forward rather than backwards.

If you don't enjoy chugging along into the future with the rest of society I would kindly suggest moving to a part of the world where they still burn wood as their primary fuel and energy source as moving backwards may just be your preference.

Joe Ratley
Joe Ratley

@Alec Sevins Hey, Alec, quit being such a "landscape-trashing" b**** and get on board, or are you REALLY a Fossil Fuel/Fool tool in disguise. It's one or the other ...  

Kevin McDonald
Kevin McDonald

I agree with you. This whole topic worldwide has been a big scam on the taxpayer and the rate payer too. It would seem to me that IF these corporate investment bankers expect to make money off this wind technology they should be the ones who solve the reliability problems of wind power and it should be required that they make this electricity a 24/7 source of power. NOT the taxpayer or the rate payer. I bet they would all abandon the ship if that was a requirement!

Why does the little guy always have to pay for the cleanup of the big greed-sters?

Kevin McDonald
Kevin McDonald

There are at least two methods that could be used now for storage of the excess electricity.

One method is already in use and has been for decades in Alaska where the entire city's grid is stored in batteries before it is distributed. This prevents a total freeze-up from occurring if the grid were to go down. It has been working for years.

Second is to utilize the existing infrastucture by simply pumping water back upstream to be stored in the same reservoirs that already supply water to the hydro-plants.

Keep in mind people that 'electricity' is NOT a form of energy. It is nothing more than a medium for delivery. It can easily be converted right back into the same form of kenetic energy of water running down-hill.

It drives me crazy to see these 'guaranteed-to-make-a-profit' public utility companies spending our money to develop some form of new technology when the technology to accomplish the task is sitting right in front of everybody already. Just use it!

Xira Arien
Xira Arien

They should upgrade the transfer system to allow other places with less wind to benefit from clean and renewable energy. 

As they mentioned they 'can't' transfer more to Cali because it's a government owned energy grid and the Republicans refuse anything that might smell like a 'stimulus'. <- my blog

Alec Sevins
Alec Sevins

@Xira Arien Many of us fail to see what's "clean" about the rampant industrialization of rural landscapes. Natural scenery looks a lot cleaner to me. Also, the construction and transport of these huge towers uses a lot of fossil fuels and doesn't seem to be accounted for in most measures. Techie environmentalists act as if they just materialize on the (permanently altered) landscape in a pure burst of sunlight, with no tangential energy usage.

David Daynard
David Daynard

They are ignoring the most logical solution, upgrade the transmission lines

Roger Bird
Roger Bird

All of these wind turbines are going to become eyesores when LENR takes over in the next 10 to 15 years.  It is as inevitable has the Sun rising tomorrow morning.

keith robot
keith robot

@Roger Bird, have you seen what coal mining does to the landscape?  Entire mountains in the Cumberland and Appalachian Mountains are being removed.  Talk about an eye-sore!  I will gladly take turbines over losing a mountain, river, and water supply any day.

Alec Sevins
Alec Sevins

@keith robot @Roger Bird This comparison comes up a lot, and I'd actually rather see (restored) mining landscapes (which at least look semi-natural) than endless acres covered with huge white towers. No, I don't deny global warming. This is about the aesthetics of the landscape.

Same goes for hydroelectric reservoirs vs. white steel skeletons all over the place, which resemble bleached dead trees in many ways. It's interesting that many of the same people who protest dams are adamant about the "green" factor of wind turbines (just more smaller generators, raised up high). They have a mental blinders that prevent them from seeing what's really happening to the landscape.

keith robot
keith robot

@Alec Sevins, I agree the aesthetics of a landscape are important, but I fail to see how a dam or a large scale mining operation is better.  Both of your examples not only destroy the aesthetics, as you are so concerned about, but also present catastrophic environmental problems that are not easily correctable.  Dams collect silt which deprives river beds downstream of properly settling which then leads to extensive erosion.  Dams also collect a huge amount of contaminants.   Mixed with the warmer waters of the reservoir, devastating algae blooms suck out all the oxygen and kill fish off in mass numbers leading to bacteria infestations and disease.

Coal mines are not any better.  Many rivers in KY and WV are destroyed from sulfuric acid, coal ash, and many other by-products of mining.  There are many towns in WV where the ground water is now toxic.  There are many rivers that have been turned to sludge from the mine waste being dumped into the waterways.   In mountain-top removal, entire mountains are removed and lost forever.  That’s not something you can just get back one day.

You complain about what looks like – but mining and dams destroy the aesthetics and the entire ecosystem with it.

Ronald Guthrie
Ronald Guthrie

One question, will this create the same problem that results with fracking? Meaning, earthquakes. After all, storing compressed air is no different than forcing chemicals into the ground to retrieve oil. So unless these underground storage areas are monitored really closely, over pressure will cause fractures to develop,and once these take place the high pressure air will travel the path of least resistance - thus creating an earthquake.

Richard Alexander
Richard Alexander

@Ronald GuthrieMy understanding is that fracking injects liquids into deposits in a deliberate attempt to fracture rock. This differs from underground compressed air storage in that the compressed air is a compressible gas, instead of an incompressible liquid, and the gas is not intended to fracture the rock.

Alec Sevins
Alec Sevins

@Richard Alexander @Ronald Guthrie Still, it would be pressure that wasn't there before, regardless of the compression factor. This has the feel of tinkering with nature and trying to solve one problem by creating another. Wind turbines have a lot of practical and aesthetic downsides. They take over far too much land in relation to their power output, and should at least be installed as close to major cities as possible, where self-righteous folk can see what they're really about.

Wind turbines are literally skyscrapers migrating to rural areas; expanding the human footprint wider than it's ever been. They are just a form of urban sprawl when you think about it. I wonder if "environmentalists" would protest tract homes built in those same areas? There's a ton of hypocrisy surrounding these large machines and you needn't be GOP to protest them.

Anthony Ricigliano
Anthony Ricigliano 1 Like

Very interesting!

Rick Moore
Rick Moore

NIMBY...  It seems that most people on this site would like to go back to a 17th century agrarian economy, except i'm sure that they want to keep their 21st century convieniences.  It seems that most large cities were so sooted up back then that pople were dying from pollution or cholera & typhus in the summer.  The rich left town for the summer.  Shut off the electric tap for one day and see how much of a crisis it becomes.   Think hurricane Sandy, Ike, Katrina.   Thank god I live inTexas where our power grid is almost 100% self-contained.  That does limit our ability to sell intrastate, but keeps our prices based upon local supply and demand, not where can Mr. Big Power sell electricity for the most money.  Unfortunately our Gas and Oil pipelines travel to the coast so that can be shipped out of here.  We generate our our own power with coal (40%), natural Gas (20%), and wind power (20%) as well as nuclear (10%).  Not enough year round water to do more than 10% hydroelectric.  All of our dams are dedicated to municipal water but some can produce electricity when releasing water for municipal customers if convienient.  Feel free to kill your own local energy capicity, we won't be selling any of ours.

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