Smart Grid Today / Published 2011 / By Karen Haywood Queen

Walmart shoppers likely will not even notice when the air-conditioning setting at their local store bumps up 4° to 78° for several hours during peak demand periods this summer. But when a company as big as Walmart, the largest private employer in the US, takes action,the reduction in demand across the grid is significant.

Walmart has DR programs in place at 1,300-1,400 of its 4,400 US stores, Jim Stanway, the giant retailer’s senior director of global energy services, told us Monday. “Per store, we can briefly put 300-400 KW back onto the grid [by decreasing usage] when we go to demand response,” Stanway said. If each store hit even one DR period in the same week, the reduction in demand across the country would be as high as 470,000 KW for that week.

For the past four or five years, the retailer has been part of DR programs with utilities across the country, he said. The system works by linking a real-time energy data system to each store’s building controls. Most of the temperature adjustments are automatic.

Customers likely do not notice the change because it takes a few hours for the temperature to increase when the setting is changed. By then, the DR period is usually over, Stanway said.

The retailer has been working to reduce its carbon footprint and bolster its green credentials through energy-saving measures and the use of alternative energy such as thin-film solar. But the main impetus for participating in such programs is to save money. Walmart declined to release its savings.

The company has real-time energy- use systems in 1,500 stores, Stanway said. “That gives us electricity consumption at the main meter and sub-circuit levels in mostly 15-minute increments and some three-minute increments,” he said.

The real-time energy data also is useful for studying the impact of Walmart’s energy-efficiency measures, Stanway said. “When we do a lighting retrofit, we can use the real-time data to study energy consumption before and after, to make sure [that] installations were done properly and [that] we get a good return on investment.”

Walmart has what it calls a daylight- harvesting program at its stores built since 1996, Stanway said. Between 2,500 and 3,000 stores have the system, which includes skylights and sensors to detect the amount of sunlight.

“Whenit’sanice,sunnyday,thesensors in the store detect the amount of sunlight and feed that data through our control system. It dims the lights,” Stanway said. “If it’s bright enough outside, the lights will actually go off. If a cloud drifts over halfway through the day, the system will adjust and the lights will start coming back on. The way it’s designed, it’s a gradual change and invisible to the customer.”

Initially the challenges included a delay of up to 15 minutes for the lights to react to the sunlight sensors,Stanway said. “Now we’re down to a few seconds,” he said. The system is made by Novar, which has a Walmart support center in Bentonville, Ark, the retailer’s headquarters.

Daylight harvesting can save up to 75% of the electric-lighting energy used by a Walmart store during daylight hours, he said. Walmart declined to disclose the cost of the system or the payback time, but each system can save an average of 800,000 KWH/year, Stanway said. At 10¢/KWH, that is $80,000/year per store. With daylight-harvesting systems in 2,500 stores — the low end of the company’s estimate of how many stores have the system — that is a companywide savings of up to $200 million/year.

Walmart also has centralized monitoring of energy use in each store, with alerts when use rises beyond normal limits. Issues that might warrant an alarm include a refrigerator case left open, Stanway said. “The system issues alarms when something is outside parameters,” he said. “Some things can be adjusted and corrected remotely.” If it cannot be fixed remotely, a technician is sent to fix it.

“Walmart’s leadership is important — they’re demonstrating that energy management is cost effective,” Miriam Horn, director of the Environmental Defense Fund’s (EDF) smart grid initiative, told us yesterday. “Walmart got ahead of the rest of the world because they put in a lot of advanced energy-management technology. Having Walmart show the way has been really important.” The EDF has a presence in Bentonville to work more closely with the retailer, she said.

Walmart is participating in DR programs in at least 10 states, Horn said. The company has also installed advanced meters in some stores at its own expense. “They make the important point that for this to work for anybody, they have to have the data and pricing information,” she said.

Having the right incentives make a key difference, too. “In our conversations with Walmart, they’ve made the point that they’re rolling out the technology where the return on investment is best,” Horn said. “They do have a business case for making these investments. They have a plan to keep expanding. In each case, it depends on the policies at the utility, state and ISO level to determine whether there’s a business case for Walmart to do it.”