Extracted from the publication of Jon R. Luoma on YALE environment 360 website July 13th 2009
For years, the stumbling block for making renewable energy practical and dependable has been how to store electricity for days when the sun isn't shining and the wind isn't blowing. But new technologies suggest this goal may finally be within reach.
For decades, “grid parity” has been the Holy Grail for alternative energy. The rap from critics was that technologies like wind and solar could not compete, dollar-for-dollar, with conventional electricity sources, such as coal and nuclear, without large government tax breaks or direct subsidies. But suddenly, with rapid technological advances and growing economies of manufacturing scale, wind power is now nearly at grid parity - meaning it costs roughly the same to generate electricity from wind as it does from coal. And the days when solar power attains grid parity may be only a half-decade away.
So with grid parity now looming, finding ways to store millions of watts of excess electricity for times when the wind doesn’t blow and the sun doesn’t shine is the new Holy Grail.
New storage approaches include improvements to existing lithium ion batteries and schemes to store energy as huge volumes of compressed air in vast geologic vaults. Another idea is to create a network of small, energy-dense batteries in tens of millions of homes. Under such a “distributed storage” scheme, utility computers could coordinate electricity flows over a “smart grid” that continually communicates with — and adjusts the flow of power to and from — local batteries. This would even include batteries in future plug-in hybrid or all-electric vehicles.
And one 2008 breakthrough could even fulfill chemists’ long-held dreams of producing a squeaky-clean and storable fuel by using excess electricity generated from renewable sources to cheaply produce hydrogen, which could then be used in fuel cells to power homes and cars.
One storage approach seems obvious: to improve battery technologies. Picture efficient, enormous batteries that can store tens of millions of watt-hours of juice. Today, the vast majority of new rooftop solar photovoltaic panels are connected to the grid, using it as a giant battery, pushing excess power onto the grid when solar panels provide excess power. The building then draws power from the grid when the sun doesn’t shine, with its meter spinning backward and forward with the ebb and flow of power. With relatively few solar roofs yet in play, utilities manage any ebb and flow by drawing down and ramping up generation at conventional power plants designed to balance fluctuating supply and demand.
A more robust world of solar and wind power might be better served by some sort of giant battery — or, more likely, many of them, widely distributed. The basic concept has been proven. Since 2003, the world’s largest battery backup has been storing energy for an entire city: Fairbanks, Alaska. Isolated as it is, and not part of any regional electricity grid, the metropolitan area of about 100,000 residents needs an electricity backstop more than most: In its sub-zero winters, pipes can freeze solid in as little as two hours. Six years ago, the city installed a huge nickel-cadmium battery, the same technology used for years in laptop computers and other portable devices. Housed in a giant warehouse, the 1,300-metric ton battery is larger than a football field, and can crank out 40 million watts of power. Still, the Fairbanks battery provides only enough electricity for about 12,000 residents for seven minutes. That was enough to prevent 81 blackouts in the city in the battery’s first two years of operation.
Still in pie-in-sky mode, there’s “vehicle to grid” storage, or “carbitrage.” This enticing notion relies on idled storage in the batteries of the millions of plug-in hybrid or all-electric automobiles that will be in use in the future. There’s reason to believe this scheme could work. More than 90 percent of the time cars sit idled, and aside from days they’re used for long trips, most of their full energy storage capacity goes unused.
A single idle, electric-powered car could generate as much as 10 kilowatts of power, enough to meet the average demand of 10 houses, according to Willett Kempton, director of the Center for Carbon-free Power Integration at the University of Delaware. With vehicle-to-grid technology, controlled by an array of smart meters, car owners plugged in at home or work could allow the grid to draw off unused chunks of power at times when short-term demand is high. Conversely, cars could be recharged when demand is low.
If advanced batteries or ultracapacitors aren’t the ultimate answer, maybe using excess electricity to make hydrogen that can be stored will do the trick. Hydrogen can be produced through simple electrolysis, but technical and cost hurdles have made electrolysis impractical. Today, industrial-scale hydrogen is produced using natural gas as a not-so-clean feedstock.
And there is progress being made on an entirely different front — using excess electricity to pump compressed air into caverns, salt domes, and old natural gas wells, and then releasing the air to help state-of-the-art natural gas power plants spin turbines, lowering the amount of fuel consumed by as much as 70 percent. A consortium of utilities in Iowa, Minnesota, and the Dakotas is already working with the U.S.’s Sandia National Laboratories to develop a giant, 268-megawatt compressed air system. Called the Iowa Stored Energy Park, it would store excess energy from the region’s burgeoning wind industry.
Read the complete entry from Jon R. Luoma on YALE environment 360 website
