Tesla has begun shipping 7kWh stationary batteries—branded by Tesla as Powerwalls—to be installed on the homes of pilot customers. The 7kWh batteries are designed for daily cycling, so they'll likely be attached to homes with solar panels, allowing owners to power their homes at night with power collected by solar panels during the day.

"Over the next few weeks, we will continue to ramp up volume production,” a Tesla spokesperson explained to Ars via e-mail, adding that 7kWh Powerwalls are initially being delivered to customers in North America, Germany, Austria, Switzerland, and Australia.

Tesla made headlines in April when it announced the stationary battery, mostly due to the battery’s price—at only $3,000, it’s considerably cheaper than other lithium-ion batteries its size. The battery can discharge 5 kilowatts during continuous use, a specification that was improved after the battery’s announcement—originally Tesla said the 7kWh battery would only discharge 2.2 kilowatts, but critics protested that the lower amount wasn’t enough to feed a household off the grid.

Tesla is also releasing a 10kWh battery intended just for backup storage for $3,500. Those batteries, which have a different internal chemistry than the 7kWh daily cycling version, won’t be available until 2016, a Tesla spokesperson told Ars.

When Tesla announced the batteries earlier this year, it noted that it would outsource their installation to third-party vendors like Solar City, which installs solar panels on homes in the US (Tesla owner Elon Musk is also the founder and chairman of Solar City). It’s unclear right now if Tesla is managing the US pilot installations itself or if it has actually begun working with other companies. At least in Australia, energy company SunEdison will be installing Powerwalls starting in November.

Before Tesla announced its battery line, it had been quietly installing and managing business-class storage batteries, which Tesla calls power packs, for companies like Jackson Family Wines since 2013.

Tesla's spokesperson wouldn't say how many household-grade Powerwalls the company intends to ship in 2015, but it cited a comment made by Tesla CEO Elon Musk earlier this year in which he said that the company has accepted 100,000 Powerwall reservations.

The company expects to produce many more Powerwalls (as well as batteries for its electric vehicles, of course) after the launch of Tesla's Gigafactory, part of which should come online in 2016. In the past two months, Tesla has signed two agreements with mining companies to develop lithium mines in Mexico and Nevada.