Tesla Motors CEO Elon Musk has launched Powerwall home battery and the company is already offering the devices to SolarCity Corp.'s customers looking for backup supply at the time the grid go down. It is expected that SolarCity will deliver them in October.

It is a new stackable battery system meant to store electricity for homes, businesses and the grid. It is a product that the company will shortly bring in billions of dollars in annual revenue.

Musk, also chairman of the San Mateo-based solar supplier, revealed that the home battery version is not expensive. Powerwall costs $3,500 for a 10-kilowatt-hour version that will enable to run a handful of home appliances for a few days in case of an outage. Particularly, that doesn't involve the cost of the inverter or installation.

Musk a year ago gave a clue with regard to what he wanted the Powerwall system should look like involving an integrated bidirectional inverter. The inverter and installation can be more than twice the price of a home storage system.

It is also sleek, as the battery is intended to be hung on a garage wall and even on an outside wall. It is 220 pounds and 7.1 inches deep. Powerwall is two inches deeper than what Musk had expected. The larger version is known as the Powerpack. Musk is looking at a big opportunity in commercial and utility-scale storage. According to Musk, the Powerpack is infinitely scalable.

Powerpack cost has not been shared. Before this event, already Tesla was the biggest giver of battery storage under California's generous subsidy program for storage projects. For Musk, Powerpack is not a new line of products.