Rooftop solar cannot heat a home in January, because the sun isn’t there when the heat is needed. Lausitz Energy Systems moves the energy across the seasons instead.
Seasonal heat storage answers a problem that stops most self-sufficiency plans at the first calculation. Jan Holub, CEO and founder of Lausitz Energy Systems, opened his Energy Tech Summit pitch with a story from his childhood in a coal mining region, shovelling fuel to keep the house warm. That early experience gave him a clear understanding of what burning things actually costs. The obvious modern fix is to heat the house from the panels on the roof. The obvious modern fix doesn’t work.
Jan Holub, CEO and founder of Lausitz Energy Systems delivering his keynote during Energy Tech Summit 2025
Why Rooftop Solar Cannot Heat a Winter
The obstacle is physics rather than engineering. “You don’t have enough sun in wintertime to heat your house.”
Batteries don’t rescue the idea either. Storing enough electricity to carry a household through a heating season would take a battery bank far beyond anything a homeowner would pay for. So instead, the system stores the energy in a different form, and moves it across months rather than hours.
The Green Heater: Storage and Heat Source in One
Holub’s answer combines both functions in a single device. The Green Heater stores energy in a hot rock core, surrounded by what the company calls controlled insulation technology.
That control is the whole invention. Insulation alone would only slow the loss of heat. Being able to regulate the heat flux from the core outward means the device can hold energy for months, then release it deliberately into the rooms around it. Charge the core from rooftop PV through the summer, and the house draws on it through winter.
The trade-off is honest and physical: the unit needs more space than a conventional heating system, because it’s not only a heat source but a high-capacity store.
Everything else in the comparison runs the other way. There are no emissions, because the input is the building’s own solar generation. There’s no energy bill either, which Holub identified as the main reason customers are interested — the system is a one-time investment made during construction. And he expects a service life exceeding fifty years, which changes how people should judge the cost.
Proof From a Tiny House
The technology has been running in a small test building since 2022, and it kept the building warm across the winter. Holub was candid that this exceeded expectations. The team never designed the tiny house to stay warm for a full season, yet it did.
That’s a modest proof point, and he presented it as one. What it establishes is the principle: controlled release from a hot rock core can carry a small building through a heating season on summer input alone.
The Market: New-Build First
Holub framed new construction as the entry point, because the device is easiest to specify while a building is still on paper. Germany builds a large number of new homes each year, and he translated that into a substantial addressable market across the DACH region.
Retrofit is the larger prize by an order of magnitude, though it comes later.
The demand signal he described was unusually direct. Construction companies, architects, and homebuilders planning houses two or three years out keep asking the same question: when can we buy it? The team is now planning an educational building around the technology, powered entirely by rooftop PV. The client’s motivation is straightforward: knowing today exactly what heating that building will cost for the next fifty years.
The most telling anecdote came from a meeting with a construction company. Holub had finished explaining the technology and was leaving when they called him back to ask whether they could invest in the company.
Where the Company Stands
With the tiny house proving the concept, the team is now building its first office building. That serves two purposes: finishing development at a realistic scale, and giving people a place to go and see the technology, since the approach is still new enough that they keep asking.
Production planning is running in parallel, and the company is targeting market entry for the end of 2026. The founding team comes largely out of the semiconductor industry, and Holub noted that part of the technology originates there. Colleagues on the team cover industrial energy projects, thermal modelling and simulation, electronics, and software.
Jan Holub speaking during Energy Tech Summit 2025
Takeaway
Seasonal heat storage is a timing problem dressed up as an energy problem. The sun delivers more than a house needs in July, and almost nothing it can use in January. Batteries are the wrong tool for a gap measured in months. Storing the energy as heat in a rock core, and controlling how slowly it comes back out, sidesteps the mismatch entirely. Whether it scales is a manufacturing and cost question rather than a physics one — and the first office building exists to answer exactly that question.
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