Joulzen Repurposes Tanks for Smart Energy Storage

Vienna-based startup Joulzen is redefining thermal energy storage by repurposing existing infrastructure, such as former oil tanks, into intelligent components of a decentralized energy network. This innovative approach tackles a critical challenge in the energy transition: efficient and sustainable heat storage. By transforming disused vessels into high-capacity thermal batteries, Joulzen aims to significantly reduce heating costs and carbon footprints for households.

The company's core technology centers on integrating these repurposed tanks with heat pumps and advanced, model-predictive control systems. This smart regulation leverages real-time data, including weather forecasts, electricity prices, and user consumption patterns, to optimize energy storage and release. Joulzen's solution is designed to store energy when it's cheapest or most abundant, and deploy it precisely when needed, thereby minimizing waste and maximizing cost savings for consumers. The potential for these systems to be networked into a collective 'virtual power plant' opens avenues for users to participate in energy markets and generate revenue from their stored thermal capacity.

The genesis of Joulzen stemmed from a practical observation by co-founder Florian Schellnast. Witnessing the disposal of a substantial steel tank after a heating system upgrade, he recognized the environmental and economic inefficiency of discarding such valuable materials. With a background in product development focused on circular economy principles, Schellnast envisioned a solution that would give these tanks a new, high-value purpose. This insight, coupled with the founders' academic training in innovation and business model development at TU Wien's i²c, laid the groundwork for the company's formation.

Joulzen operates across the entire value chain, positioning itself as a hardware manufacturer, software provider, and energy aggregator. This integrated model allows for end-to-end optimization of the heating system. The company highlights the substantial storage capacity of its repurposed tanks; a typical 6,000-liter oil tank can store approximately 240 kilowatt-hours of thermal energy. This capacity is considerably larger than conventional heating batteries, and crucially, is achieved at a fraction of the cost per kilowatt-hour, estimated to be 9 to 15 times lower.

The company's strategic development has been significantly bolstered by support from Austria Wirtschaftsservice (aws), particularly through its aws Preseed – Innovative Solutions and aws Seedfinancing – Innovative Solutions programs. Co-founder Sebastian Rigger emphasized the pivotal role of the initial aws funding, stating it provided crucial external validation and the necessary budget to transition Joulzen from a promising idea to a tangible project. This support has been instrumental in advancing prototype development, refining the plug-and-play control technology, and establishing a network of installation partners.

Looking ahead, Joulzen aims to scale its operations across Europe, envisioning a future where nearly every heating system functions as a climate-positive energy hub. The company successfully onboarded its first paying customers in early 2026 and plans to launch its fully integrated, series-produced energy systems—comprising thermal batteries and smart heat pumps—in the summer of the same year. This expansion is supported by a network of local installation firms, ensuring seamless integration and customer support. The ultimate goal is to demonstrate the scalability and widespread applicability of their innovative thermal storage solution.