One evening in late February 2008, the famously steady winds of west Texas began to wane until, at last, hundreds of giant wind turbines were becalmed – their enormous blades slowed or stilled.

In just three hours, grid operators at the Electric Reliability Council of Texas watched wind power output fall by 1,400 megawatts – power needed to supply roughly 600,000 homes. Following emergency procedures, a blackout was avoided by quickly cutting power to several industrial customers.

But the incident highlighted renewable energy’s Achilles’ heel: Intermittent solar and wind power requires backups. It’s not a big problem today with solar, wind, and other renewable energies supplying less than 3 percent of the energy needs in the United States. Yet it could be a big problem in the not-so-distant future.

If wind power supplies 20 percent or more of the nation’s power by 2020, as a US Department of Energy study last year said it could, storing backup electricity becomes critical to grid stability, experts say.

“Little attention has been given to massive electricity storage that is a key to making the use of renewable energy possible on a broad scale,” wrote the authors of an American Institute of Chemical Engineers (AICE) report on mass power storage for the grid last year. “In America today, there is an almost total absence of public awareness of the need.”

While the Obama administration presses to expand renewable energy with emphasis on growing wind farms and utility-scale solar, these efforts could vastly increase the need to build new backup power plants – much of which today involves firing up natural-gas turbines when the winds die down. The only way to avoid using fossil fuels is to develop grid storage.

Without the ability to store massive amounts of energy, “renewable power can only be piggybacked onto the US grid to supply not more than 15 percent of the power at best,” the AICE study says.

Yet the potential costs of building the storage necessary to allow renewable energy to expand to supply just 20 percent of US energy needs would be enormous – more than $340 billion to develop some 912 billion watt-hours of storage capacity, the AICE study found.

“How you store energy from wind at times when it’s not needed – and what you do when the wind stops blowing – is emerging as something that must be discussed and studied,” agrees William Smyrl, a professor of chemical engineering at the University of Minnesota in Minneapolis who is studying the issue.

Need for batteries rises

Storing cheap power on the grid and then selling it at peak times, when power is more expensive, is hardly a new idea. A handful of grid-power storage facilities across the country, including battery banks, have been set up. But the cost performance of such facilities has never been good enough for them to take off.

Yet recognition of the need is growing quickly among utilities.

“Storage will need to be part of our portfolio if going to 15 to 20 percent wind at a national level, otherwise it won’t be efficient at a lower level, and it won’t get us where we want to go environmentally,” says Arshad Mansoor, vice president for power delivery and utilization for the California-based Electric Power Research Institute, the research arm of the utility industry.

The grid has more than 22,000 megawatts of “pumped hydro” storage capacity to capture excess energy from hydro-electric dams, Dr. Mansoor says. But with environmental concerns and limited sites to build them, few see pumped hydro as a major new alternative, he says.

Conventional lead-acid batteries are too costly and have poor durability. Instead, researchers are turning to batteries with unusual chemical combinations, such as sodium-sulfur as well as the more familiar lithium-ion.

Energy experts are also eyeing other energy technologies such as compressed-air energy storage, flywheels, and molten salts that store power generated by solar-power plants. “What we need is large-scale storage in the gigawatt range – and you don’t get there using double-A batteries,” Mansoor says.

Until recently, relatively little funding has flowed to grid-storage development. In 2007, the industry overall spent a relatively tiny $2 billion on energy storage at the utility level, according to a report last year by Climate Change Business Journal. That’s starting to change.

Before the recent financial crisis, venture investing in utility-energy storage had risen from about $300 million in 2004 to nearly $700 million in 2007, according to Lux Research, a market research company.

“It’s still an incredibly hot market right now,” says Brad Roberts, chairman of the Electricity Storage Association, a trade group in Morgan Hill, Calif. He expects at least $200 million in new federal funding to accelerate development that languished with just $4 million to $10 million annually over the last 10 years.

Individual companies are accelerating their work, he says. They include A123, a company now producing lithium-ion batteries on trailers to supply ancillary power to utilities, as well as Beacon Power, another Massachusetts company developing flywheel-based systems to store grid power, he says. The big utility American Electrical Power has deployed a sodium-sulfur battery system, too.

A few researchers and utility executives are also creating and deploying some of the world’s most powerful batteries and other grid-backup systems to pick up the slack when energy generated by wind or solar wanes.

“What I’m talking about are batteries the size of a double-decker bus,” says David Bradwell, a battery expert working on grid-scale batteries with new chemistries at the Massachusetts Institute of Technology. While sodium-sulfur is a proven technology, it is still too expensive for mass power storage at around $400 per kilowatt hour, experts say. Mr. Bradwell hopes to get costs down to about $100.

“These batteries could be deployed in a large-scale system over several square miles – or individually, maybe at the base of a wind turbine or at a wind farm,” he says.

A working prototype in Minnesota

Dr. Smyrl, federal researchers, and utility executives are looking at the same renewable storage problem in Luverne, Minn., where the nation’s first wind-to-battery setup is using a small wind farm to charge batteries that release that power onto the grid.

These aren’t your ordinary flashlight batteries – but rather high-temperature, sodium-sulfur batteries the size of two semi-trailers that soak up 7.2 megawatt hours of power generated from seven nearby wind turbines owned by MinWind, a Minnesota wind-power developer.

Overseeing the project is Xcel Energy, the big Minneapolis-based utility that bought the battery from NGK Insulators, a Japanese battery supplier. Smyrl and the others are focused on how much power the sodium-sulfur system can absorb, how quickly, at what cost – and then deliver it to the grid.

Xcel’s interest is much more than academic. Wind power already accounts for 6 percent of the power flowing on its system. A year ago, Xcel’s wind capacity was at 2,700 megawatts compared with about 3,000 megawatts today – it hopes to double that amount by 2020.

Congress is also widely expected to pass legislation requiring utilities to derive perhaps 20 percent of their power from renewable sources by 2021. Even without federal legislation, however, state mandates in nearly half of the states already require a significant percentage of renewable power. In Minnesota, where Xcel sells a lot of power, the state’s renewable portfolio standard calls for 25 percent renewable power by 2025.

“The direction we’re heading [with the battery test] is to meet these state mandates and hopefully going beyond them,” says Frank Novachek, Xcel’s director of corporate planning. “This will help put us in a very good position to meet whatever happens on a federal basis.”