At FOSDEM 2025, Nicolas Höning from Seita Energy Flexibility took the stage in the Energy Devroom to discuss the challenges and opportunities surrounding the adoption of the S2 energy flexibility protocol. His talk, titled “From the Battlelines of the S2 Energy Flexibility Protocol Adoption,” focused on the LF Energy FlexMeasures project and the role of open standards in accelerating innovation in home energy management. A summary follows, and the full video is embedded at the end of this post.
The Importance of Open Standards
Höning began by underscoring the significance of open standards in the energy sector. He pointed out that open standards facilitate large-scale innovation and interoperability, ensuring that various systems and stakeholders can work together efficiently. However, he also acknowledged the inherent challenges, including competing standards and regulatory hurdles.
The Landscape of Home Energy Management Standards
While the discussion centered on S2, Höning provided an overview of the broader home energy management (HEM) standardization landscape. He compared S2 with other standards such as OpenADR and EEBus, explaining that each serves different roles:
- OpenADR primarily addresses grid-side flexibility, enabling communication between demand response aggregators and the grid.
- EEBus has a strong presence in Germany, backed by major industry players, and focuses on in-home energy coordination.
- S2, in contrast, aims to simplify and standardize communication between home energy devices, facilitating flexibility at the residential level.
The Role of Open Source in Standard Adoption
A key theme of the talk was the role of open source software in accelerating the adoption of open standards. Höning argued that successful standards require not only regulatory backing and industry adoption but also a strong developer community driving innovation. He likened this to the historical shift from XML and SOAP to more lightweight web technologies driven by developer preference.
Introducing the S2 Protocol
Vlatko Bratanov, a Seita engineer, provided a deep dive into the S2 protocol itself. S2 introduces a structured way to define the flexibility of in-home energy devices through eight generic flexibility capabilities, including:
- Power modulation
- Energy storage
- Load shifting
- Alternative energy source selection
These capabilities are distilled into five control types, which manufacturers can implement to define how their devices interact with a home energy management system (HEMS). Bratanov emphasized that S2 is designed to be simple yet powerful enough to accommodate a wide range of home energy devices, from heat pumps to battery storage and EV chargers.
Real-World Implementations
The presentation highlighted several real-world implementations of S2, including:
- A Grid Congestion Management Project: A closed source initiative using S2 to optimize energy usage in neighborhoods.
- The Tunes Project: A hybrid open source/closed source project demonstrating S2 integration with heat pumps and thermal buffers.
- The Klin Project: Seita’s open source initiative to develop an S2-compliant HEMS with advanced scheduling capabilities, including an algorithm called profile steering for optimized energy management.
The Path Forward
The talk concluded with a call to action for developers, manufacturers, and policymakers to contribute to the growth of S2. The speakers acknowledged the chicken-and-egg problem – hardware vendors hesitate to adopt S2 without widespread software support, while developers need real-world devices to validate their implementations. However, they expressed optimism that through open source collaboration, S2 could become a widely accepted standard in home energy management.
Get Involved
For those interested in contributing, the speakers pointed to several open source projects related to S2:
- S2 Python: A library supporting S2 messaging and control types.
- FlexMeasures: A powerful scheduling and forecasting tool integrating S2.
- Home Assistant Integration: Efforts to bring S2 compatibility to one of the most popular open source smart home platforms.
