Melbourne's first Powerwall 2 has been installed at a three-bedroom, one storey house in Coburg. Brendan Fahey and his wife Josephine added Tesla's shiny new battery to their home to complement their existing solar panels, after Brendan calculated that the Powerwall 2 could take his energy bill down almost to zero.

Tesla's Powerwall 2 was announced in October 2016, a follow-up to the original Powerwall, launched in 2015. The new model has improved on the original in a number of ways. One of the biggest changes is a built-in inverter, where the original model required an external one. The Powerwall 2 almost doubles the capacity of its predecessor, upgrading from 7kWh to a full 14kWh (13.5kWh of which is usable capacity). With Australia's average household electricity usage estimated to be around 16kWh a day, or as low as 13.5kWh in Victoria, the Powerwall 2 is now offering enough storage for Aussie households to potentially offset their entire electricity bill, and perhaps even move off the grid.

This is what Brendan found when he crunched the numbers around adding a Powerwall 2 to his existing solar. "I did some calculations with Powerwall 2 by writing a little formula based on my solar production and electricity usage for each day from 1st December 2016," Brendan explains. "Starting with a 14kWh home battery I subtracted and added on the gains and losses as I went through the six months up until a few weeks ago. At no point in my calculations did the 14kWh battery run out. If I had owned Powerwall 2 during that time I would have had no electricity bill."

Of course while Tesla and the Powerwall are big names in home energy storage, they're certainly not the only players on the field. One of the big stories the week of the Powerwall 2's launch pointed out that Tesla's shiny new battery had already been beaten on price by a competitor — an Australian made battery called the Ampetus "Super" Lithium. Based on SolarQuotes' solar battery comparison table, the Ampetus, a $2300, 3kWh battery has the lowest cost per warranted kWh of all the batteries currently on the market, at 19c. Tesla's Powerwall 2 is a close second at 23c per warranted kWh.