Company says 7kWH energy storage unit, which uses lithium-ion battery to store energy from rooftop solar panels, will be available by end of year Australia will be one of the first countries in the world to get Tesla’s vaunted Powerwall battery storage system, as several other companies scramble to sign up Australia’s growing number of households with solar rooftops. US firm Tesla said that its 7kWH home energy storage units would be available by the…