A Southern California mall just started using two big battery systems from electric car company Tesla to manage energy.

Commercial real estate developer Simon Property announced on Wednesday that its Brea Mall, in Brea, Calif., 30 miles southeast of Los Angeles, would use the batteries to provide energy to buildings during certain times of day.

Tesla packages lithium-ion batteries manufactured by Panasonic—the same ones it uses in its electric cars—into battery packs that can be operated by smart software. Last year, Tesla announced that it would start selling these battery packs to utilities, building owners, and even home owners.

The mall’s new Tesla batteries, called “Powerpacks,” will be charged from the grid during hours when electricity rates are low. When rates are high, the packs will be tapped to provide energy for the mall’s operations, presumably lights and air conditioning.

By switching buildings to battery power, and off of the grid during more expensive times of day, building owners can save money on their monthly energy bills.

For more on Tesla’s new high energy battery pack watch our video.

Simon SPG says that the Tesla batteries will save the company thousands of dollars annually. Simon’s Tesla batteries have a capacity for 250 kilowatts and 500 kilowatts of energy each, which is about 5 Powerpacks and 10 Powerpacks respectively.

Tesla started assembling small numbers of its Powerpacks last year at its massive battery factory, called the Gigafactory, which is under construction outside of Reno, Nev. Eventually, it will use batteries that are made on site.

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Tesla also sells a Powerwall version of the battery pack for homeowners and small businesses.

While Tesla currently sells a relatively small number of Powerpacks and Powerwalls, its CEO, Elon Musk, has said he expects sales of energy products to increase faster than the that of the core car business.