On the morning of Thursday 22 October 2026, about 400 people in Wildpoldsried, a village in the Allgäu, were told that sonnen had filed an insolvency application. Two months earlier, Shell had sold it. So how did the “Tesla of solar storage” run out of road while its American arm kept on growing?
95/100FiledBANKRUPT MeterA court process has begun.
By Max Noble · 27 October 2026 · 5 minutes
1The company
Sunshine, in a box.
sonnen makes home batteries that store the power from solar panels on the roof. Christoph Ostermann and Torsten Stiefenhofer founded it in Wildpoldsried in 2010. More than 150,000 customers use its systems.
2What it promised
A famous owner, and a bigger future.
In February 2019 Shell agreed to buy all of sonnen. Both sides promised growth.
Full ownership of sonnen will allow us to offer more choice to customers seeking reliable, affordable and cleaner energy.Shell, 15 Feb 2019
Shell sold it in August 2026
Shell New Energies is the perfect partner for helping us grow in a market that is expanding rapidly.sonnen’s co-founder and chief executive, 15 Feb 2019
German sales fell by more than two-thirds in 2024
Service for more than 150,000 existing customers is to continuesonnen, as reported on 22 Oct 2026
Too early to judge
One minute read. Four to go.
Your turn · BANKRUPT: The Survivor Game
🇩🇪 Germany · Home batteriessonnen95MetersonnenHome batteriesWarningSales, 2024 vs 2023−70%Two months after Shell sold it, it went to court because it could not pay its bills. Read the story↗︎
🇩🇪 Germany · Home batteriessonnen95MetersonnenHome batteriesDeadlineVerdict day · 30 April 2027185 daysWhat to watch: Whether a court opens proceedings, and whom it names to oversee them.
🇩🇪 Germany · Home batteriessonnen95MetersonnenHome batteries
Will sonnen find a buyer or a rescue by 30 April?
Yes meansA buyer or a rescue deal keeps sonnen going by 30 Apr 2027.
Max Noble Odds: 34% chance of Yes. They move with every call. Against the odds you win more, and lose more.
The small print, in plain words
The trouble
sonnen could not pay its bills. Its sales fell by more than two thirds in 2024 and its losses grew. Two months after Shell sold it, it filed for bankruptcy.
Yes means
A buyer or a rescue deal keeps sonnen going by 30 Apr 2027.
Split last year’s revenue into one-off sales and money that comes back every year. If most of it is one-off, and a rival sells the same thing for less, you are exposed. This week, list what customers would pay you for after the sale, and put a price on one of those services.
In your investments
Before you put money into a company that makes hardware, check its market share over three years and how much of its revenue repeats. A falling share with no repeat income is a warning sign, however good the product. Check whether the owner keeps putting money in, because that can hide what the business earns on its own.
In your career
If you run a product line, do not let your career rest on the box alone: learn the service side and the numbers behind it. If your product is already being copied for less, propose a service model now, with a small test. If you have already defended the box too long, say so first and bring the new plan with you.
Subscribe free to the Morning Warning List and read the other four minutes now. Every Monday and Thursday at 05:00, you get the list and the next story. When a company's own documents show the danger before any filing, you get a First Warning.
The year sales fell by more than two-thirds, in one chart
What the owner paid in to keep the lights on
Three moves before the court decides
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Free. No noise. One reply is enough to leave the list. Not investment advice.
3What it delivered
A record year. Then the floor gave way.
In 2016 sonnen began linking its customers’ batteries, so that homes could share their spare solar power. It was the clever part of the business.
In Germany, though, the company still lived mostly on selling the box. In 2023 sonnen GmbH’s sales reached about €264 million, its filed accounts show.
In 2024 they fell to about €78 million. The German market for home batteries shrank by only about 6% that year, pv magazine reported.
Its costs did not fall with its sales. Staff costs stayed at about €52 million. The loss for the year was more than €100 million.
sonnen GmbH sales (€m)
Down by more than two-thirds in one year. The German company only, not the group. Source: sonnen GmbH accounts 2024.
Profit or loss, sonnen GmbH (€m)
The loss grew twelvefold. Source: sonnen GmbH accounts 2024.
4Why it’s on the list
Cheaper boxes, and an owner on the way out.
Asian makers took the German market. In 2025 BYD held about 16.5% of it, and sonnen about 3.3%, a study for pv magazine found. In 2024 sonnen still had 4.7%.
The owner paid the bills. In 2024 the money its owner had put into sonnen GmbH rose by about €72 million, the accounts show. At the end of that year, sonnen GmbH had about €4 million in the bank.
The sun shines just as brightly into a cheaper box.
In September 2023 Shell looked for a buyer, Handelsblatt reported. In August 2026 it sold sonnen to TIVEN, the family office of Aurelius co-founder Gert Purkert. The price was not disclosed.
On 22 October 2026 sonnen GmbH filed an insolvency application. The company confirmed it to Handelsblatt. Several subsidiaries are to be wound down, and only one production site is to remain, Handelsblatt reported.
On the same day, sonnen USA said its sales had roughly doubled. Its growth comes largely from virtual power plants: thousands of home batteries run together for the grid.
How sonnen reached the court
Two months from sale to filing. Sources: Wikipedia; Shell; ESS News; Handelsblatt via zfk and Electrek.
5What it should do now
Three moves before the court decides.
1
Keep the 150,000 customers whole.
Tell every owner and installer, in plain words, who answers the phone and how the warranty works now. The customers are the most valuable thing left.
2
Sell the service, not just the box.
The American arm grows on power-plant services. Build the German business around the batteries already on German walls.
3
Make only what pays.
Build batteries only where each one earns its keep. A box sold at a loss is a donation with a warranty.
BANKRUPT Law No. 20
Sell the Service Before the Box Gets Cheap
Wildpoldsried, 2010. In a village in the Allgäu, two men founded a company to store the sun in a box. By 2016 its customers could share their spare solar power with one another. In 2019 Shell bought the whole company. At home, though, it still lived mostly on selling boxes. Then Asian makers learned to build the box for less. In 2024 its German company’s sales fell from about €264 million to about €78 million. On 22 October 2026 it filed an insolvency application. That same day, its American arm, built on power-plant services, said its sales had roughly doubled. A box that earns once is, financially speaking, a beautifully engineered doorstop. Sell the service before the box gets cheap.
— Max Noble
sonnen built a service that could pay every year, but in Germany it kept living on a box that paid once, and rivals made the box cheaper.
Do you earn most of your money from a product a rival could make cheaper?
This question is about your company, not sonnen.
In your company
Split last year’s revenue into one-off sales and money that comes back every year. If most of it is one-off, and a rival sells the same thing for less, you are exposed. This week, list what customers would pay you for after the sale, and put a price on one of those services.
In your investments
Before you put money into a company that makes hardware, check its market share over three years and how much of its revenue repeats. A falling share with no repeat income is a warning sign, however good the product. Check whether the owner keeps putting money in, because that can hide what the business earns on its own.
In your career
If you run a product line, do not let your career rest on the box alone: learn the service side and the numbers behind it. If your product is already being copied for less, propose a service model now, with a small test. If you have already defended the box too long, say so first and bring the new plan with you.
sonnen GmbH accounts 2024 (balance sheet and income statement, with 2023): sales €263.5m → €78.4m; loss €8.8m → €106.6m; staff costs €52.6m → €52.3m; cash €3.9m; capital reserve €205.3m → €277.2m · lobbyregister.bundestag.de
zfk, 22 Oct 2026: filing confirmed to Handelsblatt; staff told that morning; about 400 at headquarters; “Tesla der Solarspeicher”; Shell bought it in 2019; sold to TIVEN, family office of Gert Purkert · zfk.de
Münster Aktuell, 22 Oct 2026: about 400 staff informed; service for more than 150,000 customers to continue; sales and loss 2023–24; warranties · ms-aktuell.de
Electrek, 22 Oct 2026: filing two months after the sale; subsidiaries and one remaining site; sonnen USA sales roughly doubled, driven by virtual power plants · electrek.co
Energy-Storage.News, 23 Oct 2026: Shell sought buyers in September 2023 (Handelsblatt); sale to TIVEN in August 2026, price not disclosed · energy-storage.news
ESS News, 28 Aug 2026: Shell sells sonnen to TIVEN and Aurelius WaterRise · ess-news.com
Shell and sonnen, 15 Feb 2019: Shell agrees to acquire sonnen; quotes · sonnenusa.com
pv magazine, 26 Jun 2026: German home-storage market shares 2025 (P3 and RWTH Aachen): BYD 16.5%, sonnen 3.3% · pv-magazine.de
pv magazine, 5 May 2025: German home-storage market fell about 6% in 2024; sonnen 4.7%; Asian makers over 50% · pv-magazine.de
Wikipedia: Sonnen GmbH (founding in 2010, founders, sonnenCommunity in 2016) · en.wikipedia.org
sonnen GmbH has filed an insolvency application; no court had opened proceedings or named an administrator when this was written. The figures are for sonnen GmbH, the German company, not the whole group. The three moves and the law are Max Noble’s analysis. Not investment advice.
BANKRUPT: The Survivor Game · by Max Noble
Your turn. Does sonnen survive?
Filed 5 days ago. Make your call, beat the other players, and climb the board.
Pick one, then see what the other players chose and which move I would make.
The read-the-story quiz
Three points for each right answer. Your first answer counts.
Where it could bite you · BANKRUPT Law No. 20
Sell the Service Before the Box Gets Cheap
The same mistake, in your own world. Free, from the book.
In your company
Split last year’s revenue into one-off sales and money that comes back every year. If most of it is one-off, and a rival sells the same thing for less, you are exposed. This week, list what customers would pay you for after the sale, and put a price on one of those services.
In your investments
Before you put money into a company that makes hardware, check its market share over three years and how much of its revenue repeats. A falling share with no repeat income is a warning sign, however good the product. Check whether the owner keeps putting money in, because that can hide what the business earns on its own.
In your career
If you run a product line, do not let your career rest on the box alone: learn the service side and the numbers behind it. If your product is already being copied for less, propose a service model now, with a small test. If you have already defended the box too long, say so first and bring the new plan with you.
Buy the bookThe full chapter, with the case, the way back and the keys, is in The 42 Laws of BANKRUPT.
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