New case study highlights how open source innovation is helping modernize Europe’s electricity grids and accelerate the energy transition
AMSTERDAM / SAN FRANCISCO — April 23, 2026 — TenneT, one of Europe’s leading transmission system operators (TSOs), has successfully deployed a new in-house grid security analysis platform called ReFlow, achieving at least a 10× performance improvement across key operational processes. Built using PowSyBl, the open source grid modelling and simulation framework hosted by LF Energy, the system moved from project initiation to first production release in just five months.
ReFlow was developed to help TenneT address rising operational complexity driven by Europe’s accelerating energy transition, including increasing renewable generation, higher data volumes, tighter time-resolution requirements, and growing grid congestion.
The platform automates large-scale grid security studies by orchestrating multiple parallel calculations using PowSyBl, dynamically scaling computing resources as needed. Compared with previous tooling, TenneT reports significant gains in speed, flexibility, and operational efficiency.
“The open source model allowed us to adopt a state-of-the-art solution without a lengthy procurement process,” said Hugo Pfister, Manager Grid Security Applications at TenneT Netherlands. “It gives us the flexibility to adapt and extend the tooling to our specific needs, while also promoting knowledge sharing across the industry.”
Accelerating Grid Modernization Through Open Source
At the core of ReFlow is PowSyBl (Power Systems Blocks), an open source Java-based framework used for electrical grid modelling, load flow analysis, contingency analysis, capacity calculation, and other mission-critical applications.
Originally developed by RTE, PowSyBl is now hosted under neutral governance by LF Energy and is already used in production by multiple European TSOs and regional coordination centres.
The modular architecture of ReFlow also allows TenneT to integrate future analytical engines for dynamic security assessment, short-circuit analysis, and other evolving grid requirements.
Built for Speed and Scale
TenneT credited two major factors for the rapid five-month deployment timeline:
- Access to a modern on-premises cloud-native platform including Kubernetes, Kafka, and S3-compatible storage
- A development team embedded directly within business operations, allowing close alignment between software engineering and grid operations expertise
This structure reduced traditional IT-to-operations handoff delays and enabled faster refinement of analytical workflows.
What Comes Next: Nexus
TenneT is now developing Nexus, a new operator-facing interface that will integrate ReFlow’s analytical capabilities directly into daily operational workflows. Nexus is designed to provide grid operators with a unified view of security and congestion insights to support faster, better-informed decisions.
About TenneT
TenneT TSO B.V. operates the high-voltage electricity transmission network in the Netherlands and a large part of Germany. The company plays a critical role in maintaining reliability, enabling renewable integration, and supporting Europe’s decarbonization goals. Learn more at tennet.eu.
About PowSyBl
PowSyBl (Power Systems Blocks) is an open source framework for modelling power systems, performing power flow calculations, running contingency analyses, and supporting capacity calculation. It is used in production by multiple European TSOs and coordination centres. Learn more at powsybl.org.
About LF Energy
LF Energy is an open source foundation focused on the power systems sector and is part of the Linux Foundation. LF Energy provides a neutral, collaborative community to build the shared digital infrastructure needed to modernize the grid and accelerate the global energy transition. Its projects support utilities, grid operators, and technology providers worldwide. Learn more at lfenergy.org.
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