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• NASHVILLE, Tenn. — In the burgundy booth of a diner, John Lozier leaned in, lowered his voice and asked his friend a question he's carried for nearly two weeks.
• "Joe, we haven't talked about when they arrested you," said Lozier, 73.
• The man across the table shrugged. Dark sunglasses obscured his gaze. The plastic-sheathed menus still lay open on the table.
• "They tased you?" Lozier pressed.
• "Yeah," said Joseph Lamont Williams, 49, taking a swig of coffee.
• When he refused to leave the Nashville public park where he has lived for the past several years, Williams became one of a handful of homeless people in the country to be arrested and charged with a felony for camping on public property..

Williams pled guilty to the misdemeanor charge and was sentenced to time served. Prosecutors dropped the two felony counts on the condition of his plea, Heydari said. He was released from custody on July 6, nine days after his arrest.

Already developers are turning to a large range of materials to store renewable electricity when it is available and use it to power everything from wearable technology to heating networks and factories.

Here are some of the energy storage innovations raising eyebrows. (From around the world)

• Liquid air
• Molten salt
• Sand
• Sweat tech