Last week, the Australian Energy Market Operator (AEMO) released an initial report (PDF) on the performance of the 129MWh Hornsdale battery system that was installed by Tesla last November. It seems the market operator is pleased with the new battery, writing that the service provided by the battery system "is both rapid and precise, compared to the service typically provided by a conventional synchronous generation unit."

A conventional synchronous generation unit refers to a spinning generator, like a coal or a natural gas plant. If there's excess demand for electricity, sometimes these generators can increase their output if there's some headroom, or grid managers can bring so-called "peaker plants" online to help meet peak demand.

But often these units need a little bit of time to start spinning at the appropriate rate. Batteries, on the other hand, have the advantage that they can start putting power on the grid right away; no need to wait for ramping up. Tesla's installation in particular can rapidly discharge 100MW for about 75 minutes. It's also charged by the wind farm that's right next door.

Case study at Hornsdale

AEMO hasn't yet had to use the battery to dispatch power in an outage or to rapidly rescue grid frequency from falling beneath 49Hz (a situation that would cause an outage). This is a good thing—both of those situations would be emergencies, and grids work best when disruption is kept to a minimum.

Instead, over this recent Australian summer (December through March in the Northern Hemisphere), AEMO used the Tesla battery installation at the Hornsdale Wind Farm to provide incremental "Frequency Control Ancillary Services," which add small amounts of power to the grid to make sure frequency stays right around 50Hz on average. (Recent events in Europe have shown us just how important it is to make sure grid frequency is maintained at its pre-determined average, even if the deviations from average haven't been enough to cause blackouts.)

The most dramatic instance of this happened on December 18, when a 689MW coal generator in New South Wales tripped, causing a sudden loss of power from that power station. Such a trip generally isn't a catastrophe because there's a market for replacing that power: AEMO will pay extra for additional Frequency Control Ancillary Services to maintain the preferred average frequency. In an email to Ars, a media spokesperson for AEMO said, "While a 689MW generator trip is a relatively big event for the system, AEMO is able to meet the system frequency standard of 49.5Hz or higher for such events."

So Tesla's Hornsdale installation didn't have to rescue Australia from blackouts this summer like the blackouts the nation had in the summer of 2016, but AEMO says Tesla's battery responds to more frequent incremental needs much faster than traditional generators. Check out the graphs below to see how quickly the battery was able to meet targets for frequency regulation over an hour compared to how quickly conventional generation responded. (Conventional generation is first, click through to see the battery graph.)

Australian Energy Market Operator

Australian Energy Market Operator

AEMO also shared a graph showing how quickly the Tesla battery responded to the 689MW plant trip. You can see that as frequency declines, the battery starts feeding power to the grid.

What do you get if you’re better?

This improved performance does suggest that batteries offer something of value beyond what traditional generation offers. According to the Sydney Morning Herald, Tesla has reportedly complained to AEMO that fossil fuel rates for frequency control services don't really compensate batteries appropriately. And AEMO seems to admit this in its recent report, writing that "high response capability is not recognized or rewarded differently to the service provided by conventional synchronous generation."

Although AEMO seemed to indicate that funding for the Tesla battery was made clear during the development of the project, the operator also seemed open to changing for future battery installations. "[M]arket arrangements could also be modified to specifically recognize the rapid and accurate response capabilities of batteries, and therefore enhance their ability to earn income from providing them."

Although AEMO said care would need to be taken in any attempt to change existing market pricing, the group agreed to "work with industry to undertake formal consultation on the necessary modifications."