Last week, Tesla launched their Powerwall 2.0 residential battery storage system, a little less than a year after Powerwall 1.0.

Compared to Powerwall 1.0, peak power has increased by 40 per cent, continuous power by 50 per cent, storage capacity by 100 per cent (to 14 kWh) and an inverter is included. And all this for US$5,500 ($A8,800) – about the same price as Powerwall 1.0.

In other words, the price per kWh stored and re-used has halved in less than a year. Indicative installed prices in Australia are a little over $10,000. The commonly accepted wisdom was that battery costs would decline more gradually than the precipitate decline seen in solar PV costs. This has been proved wrong.

Let’s do a solar PV+battery+grid versus grid-only price comparison.

First, let’s assume a 4,800kWh per year household in Adelaide and that its electricity bill is either the average of all 77 market offers after all conditional discounts, or the average of all 77 Market Offers before all conditional discounts, from the 16 retailers operating in Adelaide (data from MarkIntell).

For solar PV, let’s take the median installed price of a 5kW system (data from Solar Choice) and let’s assume a 20 year life with zero residual and 20% purchase premium for on-going maintenance. For battery, let’s take the indicative installed price ($A10,300) and assume a 10 year life with zero residual.

Let’s also assume an operating regime that sets the daily household consumption against solar PV production and battery storage as far as possible. This results in 8,373 kWh per year solar production, 200kWh of grid purchases and 3,773kWh per year of solar PV export to the grid.

Putting this together and annuitising the capital items at 2 per cent real (the typical mortgage rate), we get the result shown in the chart below: PV+battery+grid is level-pegging with the average grid-only Market Offer (after conditional discounts) and cheaper than the average grid-only Market Offer (before conditional discounts).

This is astounding.

A typical household in the suburbs of Adelaide can now meet its electrical needs with solar and battery storage for about the same amount they would pay on a competitive offer from the grid.

And no need to worry about black outs or bill shock: for an outlay of around $16k and assuming a suitable roof, consumers will be able to reduce their grid bill to almost nothing (revenue from surplus PV exports paying for the grid fixed charge plus the little energy bought from the grid to cover rainy days). And the set-up more than pays its way.

Of course one can argue with any of the assumptions I have made, but they seem plausible to me and the calculation itself is not tricky.

Electricity in Australia is deeply interesting at the moment. Of all the fascinating issues competing for attention, this tops my list.

It has obviously profound implications for consumers, PV and battery producers and installers, electricity retailers, centrally dispatched generators, network service providers, market operators, regulators and governments.

The strategic and commercial implications are marvellous or frightening, depending on your vested interest. It’s worthwhile studying this carefully.

Bruce Mountain is the Director of CME and co-founder of MarkIntell.

Update: The chart below has been updated to include GST on electricity purchases, which the first chart did not.

As the author writes: “The initial chart had included General Sales Tax on battery and PV but not on electricity purchases. The revised chart accounts for the fact that the majority of households will not be able to deduct GST on their electricity purchases. By properly account for taxes in this way, the gap between PV+battery+grid versus grid-only is larger than initially calculated.”