For decades, the power supplied to homes and businesses here has been a special form of alternating current -- it alternated between on and off.
One of the state's most desolate towns sits at the end of the nation's electrical grid. It's served by a single 60-year-old, 60-mile-long power line that crosses some of the roughest and most inaccessible terrain in Texas.
Bad weather often knocks the line out of commission, typically in the blistering summer heat and usually at night. For decades, those power failures, which lasted a few minutes or a few hours, were part of normal life.
"We had a saying growing up," Mayor Lorenzo Hernandez said. "We'd say, 'Se fue la luz.' That means 'The light's left."'
Residents in the town on the western edge of Big Bend National Park were accustomed to the situation, but that didn't mean they liked it.
"It's not our culture to complain," the mayor said, "but it was annoying."
"You never get used to it," said Mario Nieto, whose family owns an appliance store. "Every time we saw a thunderstorm coming, we said, 'Oh no."'
This month, the power switch will be left on for good when a giant battery, built to ensure constant power to the town gets up to full operation.
When the monster battery is at full capacity, it will be capable of powering Presidio for eight hours at a time.
The $25 million, 4-megawatt sodium-sulfur battery, housed in a plain-Jane cement building on a hilltop overlooking the city, is the largest of its kind in the country. It uses an experimental technology that one day could reinforce large portions of the nation's electrical infrastructure at a fraction of the cost of retooling the whole system.
The impact goes beyond reliable power in Presidio, a town of 4,000 people where paved roads are a rarity and poverty is everywhere.
"It's symbolic," Hernandez said, "because now, we don't consider ourselves second-class citizens."
The ball got rolling after a post-midnight outage six years ago that angered Hernandez. His infant son spent the night in agony. Between the 100-degree heat, the desert winds and the swarming mosquitoes, the baby cried for hours.
Hernandez and others gently but forcefully pushed for changes from American Electrical Power, owner of the power line. The company, along with MidAmerican Energy Holdings, created Electric Transmission Texas, the joint venture that owns the monster battery.
The first improvement was a series of new roads for better access to the remote power.
And once the battery is fully charged, there's more: State utility officials have approved a $27 million replacement power line that's slated to be online in two years.
The battery is in Presidio because the town was dealt an unwinnable hand by the nation's electrical grid.
Most cities, officials say, are served by two or more lines. That redundancy means other lines can pick up the slack if one goes down. Not so in Presidio. The closest backup source is across the Mexican border, in Ojinaga, and it takes a couple of hours to connect the two systems manually.
The cost of building a second U.S. connection is prohibitive, so the best answer was the sand-colored building on a hilltop among the splotches of greasewood, mountain laurel and mesquite on the edge of town.
The new facility, said Steve Foster, ETT's onsite inspector, consists of a battery building, an inverter building, an unmanned computer-control building and a shiny new substation.
The whole complex is ringed by a chain link fence and a high-tech security system. Two cement gargoyles -- Foster's personal touch -- sit atop the battery building as silent sentinels.
The monster battery, though housed separately, is part of the substation, Foster says. It serves two purposes: back-up power in case of a line failure and leveling the quality of the electricity that's sent out to the community.
Power comes into the substation, and the battery, acting as a filter, can weed out surges or sags that can damage computers or appliances in town. The newly leveled juice then is sent back to the substation and on to the city.
The battery, which is charged by the grid, also will store power, Foster says, and if the line goes down, it will send electricity through the substation to homes and businesses.
The battery consists of 80 desk-size modules housed in a 35-foot-tall, 10,500-square-foot building. Every module holds 360 sodium-sulfur power cells. Each of those 28,800 cells can supply 1.5 volts, or the same charge of an off-the-shelf AA battery.
The concept in use here isn't novel.
"This is a very big UPS system," said Foster, referring to the backup systems used to protect computer data.
"People are used to having backup power on a smaller scale, for their computer or their home," said Ali Nourai, chairman of the Electricity Storage Association, a trade group dedicated to the technology. "This is the first time we'll have it on a city scale."
And in the long run, according to a new Energy Department report, such batteries can be placed around the country, helping defray some costs of rebuilding parts of the grid as well as helping cut costs associated with generating electricity.
Locally, residents can't wait for the new system.
Beyond comfort and convenience, City Administrator Brad Newton said, it's important for businesses that rely on it. The town's convenience store gas pumps are computer-controlled. Without power, the town has no access to gasoline.
The Presidio Independent School District -- with 30 servers and 1,500 computers fed by seven high-speed T1 Internet lines --does most of its work online, Superintendent Dennis McEntire said, and it has been hampered by the inconsistent power supply. Power outages and surges have been the bane of his existence.
"t kills servers," he said of the uneven waves of electricity that plague the town. "I burn out two or three power backup systems every year. Those cost $3,000 to $4,000 each to replace."
Beyond protecting what's there, reliable power also opens new economic doors for the city.
Newton already has had inquiries from a solar power manufacturing company. And with the city's abundant sunshine, there's opportunity for solar power to be generated here. The new battery could be used to store locally generated power, either for local use or for sale elsewhere. A state agency is interested in a pilot program to install a wind turbine in the middle of town.
None of those projects would be on the table, one resident said, without the battery serving as an anchor for future economic security.
"If you don't have the power, what businesses can you attract?" asked Carlos Nieto, a businessman and school board president. "Without consistent, constant power, we never stood a chance.
"Now, we have a sense of hope."
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