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.

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