Tesla, the electric car pioneer, has unveiled a "home battery" which the US company's founder Elon Musk said would help change the "entire energy infrastructure of the world".
The Tesla Powerwall can store power from solar panels, from the electricity grid at night when it is typically cheaper, and provide a secure back-up in the case of a power outage.
In theory, the device, which typically would fit on the wall of a garage or inside a house, could make solar-powered homes completely independent of the traditional energy grid.
"The goal is complete transformation of the entire energy infrastructure of the world, to completely sustainable zero carbon," Musk told reporters shortly before unveiling the Powerwall at an event outside Los Angeles.
Examples of the device were lined up along one side of a hall. "It looks like a beautiful sculpture on the wall," said Musk.
All the power for the evening demonstration, attended by several hundred media as well as technology world participants, came from his new batteries, hooked up to solar panels on the roof, he said.
Initially the device, which will cost $3,500, will go on sale in the US later this year. But the aim is to roll it out internationally some time next year.
Germany is seen as a key market for the product, because it has among the highest take-up of solar energy in the world, Musk said.
The Powerwall comes in 10 kWh weekly cycle and 7 kWh daily cycle models, both of which are guaranteed for 10 years and are sufficient to power most homes during peak evening hours.
"This is going to be really great for the poorest communities in the world," he said. "This allows you to be completely off grid."
Musk stressed, however, that moving advanced economies like the US away from unsustainable fossil fuels was a key goal.
"I think we should collectively do something about this ... we have this handy fusion reactor in the sky, called the sun," he said.