BY ONELL R. SOTO
Anyone who has recharged a cell phone knows you can store electricity. You charge it at night and use it during the day.
But it’s not the same when you’re talking about the power needed to run a city.
If you’re reading this by electric light — or on a desktop computer — the power that you’re using is being made this instant.
Right now, nuclear reactions in San Onofre, natural gas combustion in Otay Mesa, Escondido and other places and perhaps wind from turbines near Campo and countless solar panels scattered around the region are making the electricity that runs San Diego.
All those power plants, large and small, are strung together through a massive network of electric lines, the electric grid.
The job of matching that production to the need of a big city is a tricky one, relying on forecasts about weather and what people do.
What if you could store that power and do for the grid what millions do for their cell phones — charge at night when there’s excess power and use the power in the day?
“Cost-effective electric storage is the holy grail for our business,” San Diego Gas & Electric President Michael Niggli said in an interview with a trade publication this summer.
Indeed, the utility is looking at a variety of ways to store power — relying on some of the oldest technology for making electricity, and counting on some of the most innovative.
Without storage, when more electricity is needed, power companies increase their output, pressing into service their dirtiest and least efficient plants.
When less power is needed, they cut back, but sometimes, that’s impractical, and power is wasted.
And the system has to be big enough to deal with the needs on the hottest day, when it uses the most power.
“We’re paying for very expensive generators, and we’re paying for a very expensive transmission grid, and we don’t use it very often,” said Mike Ferry, who works on policy issues for the California Center for Sustainable Energy.
There are energy storage tactics already in place around the region.
The University of California San Diego, for instance, uses a giant water tank to store water that is cooled at night and then used to air-condition its buildings during the day. Researchers there are also working on how to integrate storage with solar and other technologies on the university’s power system.
In Otay Mesa, a cold-storage warehouse is so well insulated that it can keep food frozen for hours without running its refrigeration system when power is expensive.
And all over San Diego, SDG&E uses devices called capacitors in its system to store small amounts of power that is used to stabilize voltage.
But the big game changers will be in how to store power to deal with changes in the way we make and use electricity.
“You need to have storage for buffers to make sure you meet supply and demand in an efficient way, but our electric system is run, oddly enough, without storage,” said Janice Lin, who runs the California Energy Storage Association, an industry group.
Solar panels, wind farms and electric cars all place unprecedented demands on the system at the same time they present great opportunities for a cleaner future.
Wind blows strongest at night, when power demands are lowest. Solar output can drop in an instant if a cloud passes by.
Combine that with smart meters, appliances that can react to price fluctuations and storage and you would have the power system of the future.
As California moves toward getting a third of its electricity from renewable sources like solar and wind in a decade, storage will play an increasingly important role, said Jim Avery, who oversees how SDG&E gets the electricity it sells.
“You can probably do a lot without energy storage, but then the question becomes, are you doing it economically?” he said. “Nobody knows the optimum mix yet, because nobody has gone to 33 percent renewables with the type of diversity we’re talking about.”
The growth of storage is driven by changes in politics and technology.
Researchers are experimenting with a variety of methods for storing power, including a variety of battery chemistries, combinations of reservoirs, flywheels, compressed air stored in caverns, to determine what’s cost-effective and what will work for particular applications.
For storage to be commercially viable, it has to bring value to power companies, whether that’s in making the grid more stable or allowing a time shift that makes cheap power worth storing until prices are higher.
Earlier this month, Gov. Arnold Schwarzenegger signed a law requiring the California Public Utilities Commission to consider ordering utilities to get energy storage.
Locally, SDG&E has contracted with the San Diego Water Authority for a project designed to take advantage of the 770-foot elevation differences between two reservoirs.
Starting next year, reversible pumps can move water using cheap electricity at night from Lake Hodges to the Olivenhain Reservoir over a mile away.
The pumps then turn into generators when water flows back into Lake Hodges, making up to 40 megawatts for eight or ten hours, Avery said.
That power will replace more expensive electricity from a “peaker” plant. It also helps the grid operate more efficiently and at the proper voltage.
“There are other projects being contemplated in the county,” he said.
But such projects will always rely having enough water and geography that allows for two reservoirs next to each other.
Energy storage helps grid managers deal with big swings in power demand and production, like from day to night, but also with small ones, as when a cloud moves over a neighborhood with a lot of solar panels.
SDG&E is also working on a demonstration project tying batteries to solar panels in Borrego Springs to create a “microgrid” which could run independently of the rest of the county if needed.
The project will test what kinds of batteries are best for a variety of applications.
How well a battery can help deal with that depends on its chemistry, and where it is located.
Borrego Springs was chosen because it’s relatively isolated, from the electrical system’s perspective, from the rest of the county, and because it has a high penetration of solar systems.
Some batteries are very good at jumping into the breach if the output of solar systems falls precipitously.
So SDG&E is thinking of putting them next to solar farms, on power lines, even on utility poles, Avery said.
The company is also preparing for an influx of electric cars, which are expected to charge at night, creating a different kind of energy storage. There’s talk of being able to put power from cars scattered around the region back on the grid, but that’s years away.
For now, Avery sees their value in taking power off the grid at night, when more power is produced than needed because it’s difficult to throttle back large plants that operate most efficiently at a particular capacity.
SDG&E is also working with the California Center for Sustainable Energy and the city of San Diego to put large batteries and a solar panel at the Scripps Ranch Recreation Center.
That would give the center backup power for two days during an emergency, but also could charge up when the power is cheap, providing peak power at lower cost.
And dealing with the peaks is the key.
“It’s that last power that’s always the dirtiest and most expensive, and storage is a way to address that,” said the energy center’s Ferry.