• Shell has sold home battery maker Sonnen for a fraction of the €500 million it paid in 2019, showing that being early and well-capitalised in the energy transition hasn’t been enough on its own to guarantee a return.
• Australia’s NEM data shows the same pattern on the grid side: arbitrage spreads have collapsed 84% to 85% year on year, as coal generation runs longer than modelled and home batteries increasingly cover the evening peak that grid-scale batteries were built to capture.
• The takeaway for battery businesses and their boards is to stress-test investment cases against today’s compressed spreads rather than the numbers they were modelled or pitched on. Simply being in batteries because the energy transition is growing, betting on undiversified wholesale arbitrage revenue to carry the return, isn’t a strategy on its own; margin has to come from genuine competitive advantage such as cost position, contracting structure, service quality or diversified revenue streams.

As Rachel Williamson reported for RenewEconomy, Shell has confirmed the sale of home battery maker Sonnen to Tiven, a Munich family office owned by Aurelius founder Gert Purkert. Terms haven’t been fully disclosed, but Dealroom puts the price in the low triple-digit millions, a fraction of the €500 million Shell paid for the business in 2019, and nowhere near the €2 billion Sonnen was tipped to fetch when Shell first tried to offload it in 2023.

That’s not a rounding error. It’s one of the clearest signals yet that “buy into the energy transition and wait for the value to compound” is not, on its own, a strategy.

A cautionary tale, not an isolated one

Shell bought Sonnen in 2019 promising to scale production five to ten-fold within two years, and pitched a home battery-plus-electricity model to Australian customers years before it became mainstream. Sonnen even built a factory in the old Holden plant in Adelaide in 2018. None of it materialised at the scale promised. By 2023 Shell wanted out, and, per RenewEconomy’s reporting, Sonnen spent the years since drifting, missing the wave of demand created by Australia’s Cheaper Home Batteries rebate entirely, while picking up a run of negative customer reviews along the way.

It fits a pattern. Shell’s “Powering Progress” strategy also brought it ERM Power, a stake in solar developer Esco Pacific, the Gangarri solar farm in Queensland, and retailer Powershop, a genuine, well-funded attempt to build a clean energy business alongside the core one. Sonnen is the part of that bet Shell has now walked away from at a loss, and the lesson isn’t really about Shell’s execution. It’s about what happens when a company assumes that being early and well-capitalised in a growth thematic is enough to guarantee returns. The transition is real. The margin isn’t automatic.

Australia is showing the same dynamic from the grid side

If Sonnen is the cautionary tale on the household side, the numbers coming out of Australia’s National Electricity Market show the same pressure building on grid-scale operators, for different but related reasons.

BloombergNEF data reported by PV Magazine Australia shows battery arbitrage spreads on the NEM fell 84% in Q2 2026 versus a year earlier, down to around $60/MWh, with arbitrage revenue down 57% to $53 million and FCAS revenue down 51%. Energy-Storage.News reports price spreads collapsing 85% year on year, from roughly $342/MWh to $51/MWh, even as the grid-scale battery fleet passed 9,000MW, with over 4,600MW added in a single year.

Two forces are doing this at once. First, coal isn’t leaving as fast as modelled: continued output and speculation about extensions at plants like Yallourn and Eraring is keeping wholesale price signals softer than the business cases assumed. Second, and more structurally, home batteries are eating the evening peak that grid-scale batteries were built to arbitrage. Battery supply at 6pm now covers 8.4% of demand, up from 3.1% a year ago (a near tripling), and batteries collectively now set the wholesale price in around 39% of intervals, up from 19%. As Fluence’s Matt Grover put it, residential batteries are “competing with grid-scale projects right now.”

One developer described the current off-take market for grid-scale storage as “a bit of a bloodbath.” Lenders that were happy to gear fully merchant battery projects at 50% are pulling back because projected revenues no longer support it.

I wrote about this exact trend line a couple of weeks ago: Would an 85% drop in trading margins change your board’s battery investment decision?, using the same Q2 2025 to 2026 numbers: spreads down from $342/MWh to $51/MWh, net battery revenue down from roughly $130.5 million to $57.5 million annually, and energy charging costs up 79% as more batteries compete for the same cheap midday window. The Sonnen sale and the NEM data are the same underlying problem showing up in two different markets. Spreads could recover as coal retires on schedule or demand grows, nobody has a reliable crystal ball here, but a board’s battery business case that still assumes anything like 2024 or 2025 spreads, without having stress-tested the current numbers, is carrying a risk it may not have actually priced.

What this means for battery operators

The industry narrative has been that storage sits at the safe end of the energy transition trade: demand is structural, policy support is bipartisan, and revenue only grows as coal retires and renewables scale. Both of these stories complicate that.

As I put it in the earlier post, the questions worth asking before a board signs off are simple: what share of projected returns depends on wholesale arbitrage, has that assumption been retested against current $51/MWh regional averages rather than the spreads it was modelled on, and does the network or demand-charge case stand on its own without wholesale participation propping it up?

For anyone building a household or C&I battery business, Sonnen is the reminder that first-mover position and a well-known brand don’t protect margin once a market matures, subsidy design shifts, or a well-capitalised parent loses patience. Scale without a durable cost or service advantage is not a moat.

The battery boom is happening. Deployment numbers in Australia and globally make that undeniable. But the returns are going to concentrate with operators who’ve built genuine competitive advantage, through contracting structure, cost position, service quality or system integration, rather than those who assumed exposure to the theme would be enough. Shell’s write-down on Sonnen, and the numbers coming out of the NEM, are the same story told from two different ends of the market.

If you’re operating or investing in battery storage right now, the question worth asking isn’t “is this market growing” (it clearly is) but “what specifically protects my margin once everyone else shows up too.”

#EnergyStorage #BatteryStorage #EnergyTransition #NEM #CleanEnergy

References

Rachel Williamson, “Home battery visionary sold for a loss as oil giant gets out of clean energy”, RenewEconomy, 26 August 2026.

“Bit of a bloodbath: Big batteries feel the pinch of coal plant extensions and household battery boom”, RenewEconomy.

“BNEF report details heavy falls in battery revenue on the NEM”, PV Magazine Australia, 20 August 2026.

“Battery price spreads fall 85% in Australia’s NEM in a year as grid-scale BESS fleet passes 9000MW”, Energy-Storage.News.

Derek Thomson, “Would an 85% drop in trading margins change your board’s battery investment decision? Here’s a market trend you need to know about”, 17 August 2026.