"The aim is not really to sell that much. When the GridCredits come in it'd be great to be able to sell more but my main aim is basically to self-consume," says Luna, who lives at Daisy Hill with his wife Christina and two sons, Rafa and Andreas.

The existing system cost $18,000 to instal last April. Luna, general manager of UCG, a family-owned Brisbane-based cabling contractor that does work for NBN and Telstra, reckons he is saving about $2,500 a year on power, enough to pay it off in just over seven years.

But because of the outsize quantities of power consumed running Luna's 40 square house and charging the 90KWh Tesla, he is looking at upgrading his panels and adding a 14KWh Powerwall 2 battery - making a total of 21KWh. Powerwall 2 costs $10,000.

"That with what's generated during the day should be enough to cover my 40KWh of usage, which would be cool," Luna says. Less thirsty households could sell more surplus power to the grid.

SYDNEY, AUSTRALIA - JUNE 13: Darren Miller - pictured with Emily, Jonah and Lucy - installed batteries and a smart meter to get more use out of their solar panels when the NSW bonus solar feed tariff was cut off on 31 Dec. Pictjured on June 13, 2016 in Sydney, Australia. (Photo by Ben Rushton/Fairfax Media) Ben Rushton

Home batteries are still too few in number to make a big difference. Reposit's chief executive Dean Spaccavento said no reliable data is available but he guesstimates the number is below 10,000 - out of 1.5 million solar households.

But that should change, Spaccavento says, and the field is a hive of activity. Tesla is leading battery prices lower, US supplier Enphase ordered 70,000 for its first 12 months in Australia, and SA Power Networks is running a 100 home battery trial in the Adelaide suburb of Salisbury. Chief Scientist Alan Finkel is looking at how batteries can support the grid in his power system security review.

Reposit's control software sales are growing at 25 per cent month-on-month, led by NSW where the feed-in-tariff for selling solar power to the grid plunged from 60cKWh to 4-8c on 1 January.


The firm anticipates a further lift as less savvy customers get their first bills for 2017 and find they are paying more to their retailer because the value of their sales to the grid makes a smaller dent in their grid purchases at 25-30c retail tariffs.

Chief Scientist Alan Finkel is looking at how batteries can support the power grid as part of his review of power system security. Pictured on Tuesday 27 October 2015. Photo: Alex Ellinghausen Alex Ellinghausen

Solar psyche

Spaccavento says solar psyche - "the solar is my solar; I am not giving it to someone for 4cKWh" - will push them towards installing more batteries and software controls.

"There'll be a bill shock event and that bill shock event will drive them towards doing something about it," he says.