In the final days of testing before the big opening on Friday, the Tesla big battery in South Australia has been showing some of the capabilities that make it such an exciting addition to Australia’s main electricity grid.

As this graph above shows, Tesla and the battery’s owner Neoen followed up the testing of its charging and discharging abilities with a display of rapid changes on Wednesday evening to underline the flexibility of the 100MW/129MWh plant.

The graph charts the operations of what is known to the market as the Hornsdale Power Reserve (it is located next to Neoen’s Hornsdale wind farm). It shows a period of charging, or load (in red) and discharging, or generation (in blue).

Presumably, the aim will be to take advantage of quick changes in wholesale prices, or simply to charge up when prices are low and discharge when they are high, and to help meet peak demand (which it did later Thursday, see update below).

The battery is also contracted by the government to provide fast-response stability services to the grid. A full explainer of what it can and cannot do can be found here.

If this sounds just a little golly-gosh, it is important to note that the Australian National Energy Market has never seen anything like it.

The NEM is an ageing monolith built around slow, centralised generation and a one-way network.

Small batteries in households and scattered elsewhere around the grid, and the creation of “virtual power plants” illustrate show how that is being challenged, and the switching on of the Tesla big battery – and the others that follow – is showing just how that might change, and change rapidly, in the future.

Update: The Tesla big battery is due to open just before noon on Friday – meeting the contracted deadline of December 1 – but the launch event may have to be over after the Bureau of Meteorology forecast severed weather and thunderstorms around the same time.

Later update: Australian Energy Market Operator tweeted on Thursday that the Tesla big battery was about to deliver 70MW of “stored wind energy” to deliver into the market in Thursday’s peak, just as prices soared in Thursday amid the heat, low wind generation in South Australia and a missing coal unit at Loy Yang A.

AEMO called on the Tesla big battery to ramp up to fill in the gaps as the amount of wind generation died off and temperatures soared. It fed 70MW into one 5-minute period, and over the 30 minute settlement period (5pm) 59MW, and 11MW into the next one.

Not only did it help the grid right through a peak when there was little wind, and moderate wholesale eletricity prices, it also meant one expensive gas peaking plant did not have to be switched on.