The performance and economics of the Tesla big battery – otherwise known as the Hornsdale Power Reserve – continue to fascinate.

It is the first battery of its scale to be connected to Australia’s main grid, it’s the biggest lithium-ion battery installation in the world, and it is the pathfinder for dozens of other large-scale battery projects that will follow, including many under construction.

Further insight into the performance of the Tesla big battery – owned and operated by the privately held (but possibly soon to be floated) French renewable energy developer Neoen – have emerged in a new presentation by the Australian Energy Market Operator.

We’ve already had various assessments from private analysts, and AEMO, on the battery’s speed, accuracy and versatility, the impact of the battery in slashing peak prices in the FCAS market (frequency control and ancillary services), its share of that market, and the price reductions it has delivered to consumers.

But how much money did the Tesla big battery actually make for its owners?

It’s an important question for the battery storage industry, and the wind and solar industries, particularly as the market, indeed the need for time shifting storage emerges in markets such as Queensland, where middle of the day whole-sale prices are already falling below zero.

According to an AEMO presentation made at a Monash University forum last week, and not included in AEMO’s previous documents, the Tesla big battery earned a “gross margin” from wholesale market trading of around $2.5 million in the three months from January 1 to March 31.

It is important to note that these are AEMO estimates, and not official data from Hornsdale, nor its owner. It is not known what the folk at Neoen make of it, but it’s reasonable to assume that it is “in the ballpark.”