One year after introducing the Powerwall energy storage product, Tesla Energy has started its first wave of home installations in the U.S.

The 6.4-kilowatt-hour unit stores electricity from home solar systems and provides backup in the case of a power outage. Weighing 214 pounds and standing about 4-feet tall, it retails for around $3,000.

Tesla’s Powerwalls, and its larger Powerpacks for businesses and utilities, are made at the company’s gigafactory for battery production near Reno, Nevada. The two products are part of the Tesla Energy business unit. In the first quarter of this year, Tesla Energy delivered more than 2,500 Powerwalls and almost 100 Powerpacks in North America, Asia, Europe, and Africa, Tesla said in a letter to shareholders.

“It’s starting to ramp up,” said JB Straubel, chief technology officer and a member of Tesla’s founding team, in an interview at the gigafactory. “They are going in all around the world. It’s happening.”

Powerwalls need to be installed and hooked up by trained electricians to meet municipal regulations. The costs can add up quickly, which has fueled a certain level of skepticism about the viability of consumers purchasing Powerwalls.

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One trend that’s improving the economic appeal of Powerwalls is that some states have begun phasing out net metering, which is making energy storage more attractive. Net-metering policies, which allow residential solar customers to sell their excess solar electricity back to utilities, have limited the appeal in several states.

“The picture is rapidly changing across several markets,” said Yayoi Sekine, an analyst for Bloomberg New Energy Finance. “Changes to net-metering policies and implementation of time-of-use rates will improve the case for residential energy storage systems going forward.”