Tesla and Panasonic work closely together on battery-cell production for the carmaker's high-end electric cars.
Panasonic currently produces all cells for the Tesla Model S, and also owns a small stake in the carmaker.
It's also helping to fund Tesla's massive Nevada "Gigafactory," and will oversee cell-fabrication operations once the factory is completed.
But while Tesla and Panasonic are allies when it comes to electric cars, they could be rivals in the energy-storage business, a recent Bloomberg profile points out.
In May, Tesla Motors [NSDQ:TSLA] unveiled its Powerwall and Powerpack energy-storage battery packs for homes, businesses, and utilities.
But now Panasonic plans to sell standalone battery packs for energy storage in Europe, starting in Germany.
Tesla battery gigafactory site, Reno, Nevada, Feb 25, 2015 [photo: CC BY-NC-SA 4.0 Bob Tregilus]
Tesla CEO Elon Musk views Germany as an important market for energy storage because of its advanced consumer solar market, according to Bloomberg.
Panasonic will subsequently expand its sales to France and the U.K., as Laurent Abadie--chief of the company's European division--told Bloomberg at the recent IFA electronics show in Berlin.
The Japanese company hasn't decided when it will start sales of its energy-storage devices.
Abadie said that battery packs already available in Japan can handle up to 70 percent of a household's electricity needs, and that Panasonic hopes to eventually sell units that can completely replace grid electricity.
It's worth noting, however, that Japanese households use roughly 10 kilowatt-hours per day, while the average U.S. household consumes more than three times that amount.
Panasonic reportedly believes energy-storage business in markets outside its home country could be worth $83 million by fiscal year 2018.
Photovoltaic solar power field at Volkswagen plant in Chattanooga, Tennessee
The company will also begin selling energy-storage units in Australia in October.
Energy storage effectively increases the practicality of renewable-energy sources by allowing power to be stored for later use.
This allows users to rely on renewable energy even when it is not immediately available.
While Tesla is not the first company to try to sell battery packs for energy storage, its high public profile has brought more attention to the industry.
But Tesla won't be the only recognizable brand in the industry.
In addition to Panasonic, Mercedes-Benz also plans to sell energy-storage units, in Europe at least.