Pfitzner says for the install to be successful, it will need to reduce his energy costs by around 85 per cent. Though he's been watching his energy metre daily since the install, he says it's too soon to tell. But with a 10-year warranty and a promise to refund the difference if the Powerwall doesn't live up to expectations, Pfitzner believes it's a worthwhile investment because it allows him to sell energy back to the grid, if needed. "Ultimately, if I'm generating 25kW hours a day, storing some energy and using some, then getting a tariff for that at 5 cents but selling it for more, why wouldn't you?" he says. "I still have to pay a connection fee (to the grid). If I can cover that cost it's fine, I don't need to be an energy baron." Pfitzner is conservatively expecting it to take eight years before he can break even, but says there might be some potential to cut that number by a year or more. He put together a spreadsheet looking at the system's Return On Investment (ROI) at current prices. "Every time I added 5-10 per cent to the energy tariff it cut the ROI by four to six months," he says.

"Every time power goes up by two cents a kilowatt hour (kWh), that is six months less that I'm paying for the system, effectively." While the Powerwall might be a great way to decrease energy dependence for those with enough disposable income to afford an install, Ketan Joshi, research and communications officer at Infigen Energy, says low-income earners and other grid dependent taxpayers could face rising costs of access. "The impact on low-income earners will be reflected through grid costs," he says. "As demand decreases through people offsetting their usage from solar and storage, and people leaving the grid, the utilisation of our transmission network decreases." An enormous amount of money has been sunk into electricity grids across the country: approximately $45 billion has been spent on "poles and wires" since 2009 according to The Monthly, making it "the most expensive project this country has ever seen". Those who remain connected to the grid — including those with solar/battery systems — therefore face an increasing burden of transmission network maintenance costs.

"You pay the same, regardless of the quantity of kWh flowing through the wires," Joshi says. "Someone without enough money to afford solar/battery offset will have to face the consequences of network over-investment, despite clear forecasts that clean energy technology would be leading to a more distributed model in the near future." That's a potential problem for those who can't afford to install in new forms of distributed energy technology. "If we care about equity and fairness in our energy system, then this is something we need to think about in advance," Joshi says. The researcher also says one Powerwall is not enough to meet the peak demand of an ordinary household, turning an already expensive install into a very expensive endeavour.

According to figures from the Australian Energy Market Commission, Australians consume an average of 17.8kWh each day. That would demand three Powerwall units per home if the goal was to meet 100 per cent of demand. And according to the Federal Government's open-data project on the Powerwall and home energy consumption, the maximum evening demand for most seasons is around 9-14kW. That would require a bank of five to seven Powerwalls for 100 per cent unbroken supply. Hower Joshi says that's "not quite what the system is for". "I doubt any customer would be using the product to meet 100 per cent demand," he says. "There are size and cost limitations to meeting 100 per cent of your peak demand using this technology right now, but we're certainly headed to that point."

Which is why the energy expert claims most Australians are better off "watching and waiting". "Battery costs are, I suspect, due to pitch on a downwards trajectory that's going to shift the equation for a lot of Australians," he says.