Is That Onions You Smell? Or Battery Juice?
In addition to enabling a company to pay nighttime prices for electricity, a big battery can step in during a power emergency.
Gills Onions, a food processing company based in Oxnard, Calif., needs copious amounts of electricity for refrigeration, lighting and other jobs, and it sets an example by making its own, using onion waste. But it recently became a little greener — and more economical — by adding an enormous battery.
Gills processes about a million pounds of onions a day. Of that, about 300,000 pounds a day — the tops, bottoms and outer peels — is waste. “We slice, we dice, we whole-peel,’’ said Nikki Rodoni, a spokeswoman. Disposing of that material involved considerable labor as well as diesel fuel for the trucks, and storing it on site made the company unpopular with neighbors, she said.
So a few years ago Gills switched to squeezing the wastes to produce about 30,000 gallons of juice. It might not be to human tastes, but it is rich in sugars and attractive to bacteria.
The juice goes into a device called an anaerobic digester, basically an oxygen-free chamber, where bacteria break it down and produce methane gas. After it is cleaned and dried, the methane is fed to two fuel cells that quietly and cleanly covert it to 600 kilowatts of electricity. (The remainder of the onion waste becomes cattle feed.)
That cost $10.8 million, but it worked well. Still, at some hours, Gills needs far more than 600 kilowatts — about three times as much. Then it must buy electricity from Southern California Edison, and for Gills, that posed two problems.
One was that it was buying energy at the most expensive time of the day, weekday afternoons, when the system’s loads are high. The other is that commercial customers like Gills pay not only for energy, but also for peak capacity, or the highest level of power demand that they require in the course of a month.
So it is now taking a second, unusual approach to electricity, harnessing a gigantic battery built by Prudent Energy of Bethesda, Md. The Prudent battery is the same in principle as many others, with a liquid electrolyte that can shuttle ions back and forth to absorb current or create it. But it has external tanks to store huge volumes of electrolyte and takes up a space the size of a tennis court.
The battery can absorb or give back another 600 kilowatts for as long as six hours. Fully charged, it holds enough energy to run a large suburban house for about four months.
In California, with time-of-use rates, the electricity can be bought at night for less than half what it costs during the day. It is not pure savings because the battery loses 10 to 30 percent of the energy in the round trip from the grid to the battery and back out again on its way to the electricity-using device.
But in addition to letting the company pay nighttime prices for electricity used in the daytime, the battery provides a kind of insurance: it can step in instantaneously if one of the fuel cells unexpectedly shuts down, according to Jeff Pierson, senior vice president of Prudent. That prevents a spike in Gills’s demand from the grid and thus eliminates higher demand charges.
The two companies did not disclose the price of the battery. It will initially be owned by Prudent, with Gills having an option to buy it later. Called a vanadium battery for the material used in the electrolyte, it is the largest of its kind in the world, Mr. Pierson said. He suggested that similar ones could be installed around the country.
“This time-of-use play is not unique to California,’’ he said. “There are plenty of other places around the country where you have that sort of differential between off-peak and peak.’’
Batteries like this one have a variety of potential uses. Grid operators around the country are looking for storage devices that can accept signals to draw power off the system or give it back on short notice — usually at four-second intervals — to balance supply and demand and keep the alternating current system properly synchronized.
And on the West Coast, electric grid operators are going to greater lengths to find ways to compensate for sudden surges or drops in generation from wind or solar installations. Batteries like Prudent’s can do both, although the one at Gills is not currently set up for those tasks.
For more information:
Prudent Energy Corporation
7200 Wisconsin Avenue | 10th Floor | Bethesda, MD | 20814-7227
Main: 1-301-825-8910 | Fax: 1-301-825-8914 | www.pdenergy.com