The western Sydney computer store manager isn't alone in thinking Powerwall 2 is a fresh challenge to energy retailers like AGL Energy, Origin Energy and Energy Australia in a fast-moving market.

Energy expert Bruce Mountain says their "fabulous lunch" is coming to an end. Powerwall 2's "astounding" progress could enable a savvy rooftop solar customer to beat all discounted grid power offers, he estimates.

This scotches the view that battery technology won't move as quickly as solar panels, and brings closer the tipping point at which batteries penetrate the mass market as solar panels have done.

Like Apple vs Android

Not everyone's happy. Technology entrepreneur Simon Hackett says Powerwall 2's built-in inverter – which helps keep the cost down – could set up a standards battle to rival the one between Apple and Android in smartphones.

Our typical 4,800 kWh household in Adelaide can beat all current grid-only market offers by installing a PV and battery system and selecting the best retail offer to provide their residual grid consumption and export their PV production surplus Carbon + Energy Markets

An inverter converts direct current from a battery or solar panels into alternating current to be used at home or fed into the grid.

Mr Hackett is a shareholder of Brisbane-based Redflow, which offers a zinc bromide "flow" battery for home use which is more stable but more costly at $20,000 for a 10kWh energy storage system.


But Mr Mountain, director of Carbon + Energy Markets, said Tesla's growing scale and vertical integration would challenge rival battery and inverter vendors because they would struggle to match its prices.

He calculated that a typical Adelaide solar household with 5kW of panels and a Powerwall 2 would generate about 8400kWh of power a year, use 4800kWh, export about 3800kWh to the grid and only have to buy about 200kWh from the grid.

Simon Hackett has installed Redflow batteries at his Adelaide business park and home as a vote of faith in the technology. David Mariuz

If the household took the best grid offer, its annual cost of power would be $123 a year cheaper than the cheapest grid-only offer ($1645 a year) and $449 lower than the median grid-only offer ($1971). Mr Mountain assumed a cost of capital equal to a typical mortgage on the $16,000 up-front cost.

"In other words, our typical 4800kWh household in Adelaide can beat all current grid-only market offers by installing a PV (solar photovoltaic) and battery system and selecting the best retail offer," Mr Mountain said in an article on Reneweconomy.com.

He calculated payback periods of five years for the best retail offer is selected, 11 years for the worst offer and nine years for the median offer.

Big energy companies are fighting back with their own battery and solar offers, but Mr Mountain says households prefer to own their own panels, and they're unlikely to approach batteries differently.

For an outlay of about $16,000, a typical household in the suburbs of Adelaide can now meet its electrical needs for about the same amount they would pay on a competitive offer from the grid. Carbon + Energy Markets

Mr Vorstermans expects to pay about $9500 for his Powerwall 2 and says that he can pay it off in six years if he compares it with the cost of buying "green power" from the grid, or nine years compared with standard power.

He says Tesla is forcing the pace by going direct to consumers – like Apple – and offering a single fixed price.

"As a consumer, what's not to like?"