NEW YORK – As the mercury climbed and air conditioners devoured a near-record amount of electricity this week, the operators of New York City's power grid sent out an alert: More juice.
Grocery stores immediately dimmed their lights. Hospitals switched on emergency generators. At one 35-story skyscraper in Times Square, managers darkened the blazing billboards that illuminate Broadway, even during the day.
By 1 p.m. on Tuesday, those efforts had reduced the load on the system by an estimated 650 megawatts — enough power for about 650,000 homes.
• Click here to see photos of Americans facing the heat.
"It gave us the relief we needed in our peak hour," said Ken Klapp, a spokesman for the New York Independent System Operator, which controls the state's power grid.
The dramatic conservation effort was no spontaneous act of altruism.
Under growing programs now in place in several states, grid operators are paying select customers to conserve energy during periods of extreme stress on the system.
Some big users of electricity, like factories and college campuses, can get checks worth tens of thousands of dollars for guaranteeing power savings for a few hours on the few days a year when the grid is stretched to the limit, as it was this week during the heat wave.
Without such programs, power companies might have to cut voltage or resort to rolling blackouts to ease the load on the system.
This year, companies in the New York ISO's "demand response" program — started in 2001 — have committed themselves to saving up to 1,470 megawatts in a pinch.
"That's equivalent to the largest power plants in the state," Klapp said.
Demand response programs are not the average homeowner; participants need to prove they can deliver fairly substantial savings.
A small number of specialty companies have emerged to help carry out the program. In five years, Boston-based EnerNOC Inc. has signed up about 150 clients, including grocery stores, car-crushing operations and state universities in California.
From its command centers, the company can monitor and adjust the electrical use of its customers, including dimming lights, adjusting the air conditioning and turning on emergency generators.
"There is nonessential load all over the place that you can turn off for a few hours if you're paying attention," said chief executive Tim Healy. "Its like finding a new 50-megawatt or 100-megawatt power plant."
In New York, ConsumerPowerline sends its consultants to clients that include Macy's department store to identify subtle ways of saving power, such as adjusting the speed on ventilation fans or cooling buildings earlier in the day, before electricity use reaches its peak.
"Say one office building has 10 elevators. You can turn off two of them. People in the building might not even notice it's going on," said Reena Russell, the company's chief officer of market development.
When the New York ISO called for a power down on Tuesday afternoon, the managers of 750 Seventh Ave. switched off the dazzling electric billboards that hang over the sidewalks on three sides of the building. In 15 minutes, with the help of other adjustments, the building had reduced its power use by 250 kilowatts, enough to run 200 to 250 homes.
The building's manager, Hines Interest Limited Partnership, will split a payment with ConsumerPowerline for the power-down, which lasted until 10 p.m. But the building's director of engineering, Daniel Pugliese, said the money was not the main thing.
"We're doing this for one reason — to help out Con Ed and help out the grid," he said.
New Yorkers, after all, remember the last time the grid failed: a 2003 blackout that darkened much of the Northeast. Fear of a repeat is one reason enrollment in demand response programs has grown.
This week's heat wave did not produce a failure like 2003, though electricity use records fell left and right.
New England used a record 27,374 megawatts between 2 p.m. and 3 p.m. on Tuesday. New York set a record of 32,624 megawatts on Monday and would have easily exceeded that Tuesday if not for its conservation program.
Klapp said the New York system would have survived this week's heat even without the savings, but the operators did not want to cut it close.
"You always want to have that cushion in your back pocket in case a generator gives out or a transmission wire trips," he said.