A team from Open Energy Transition discusses the benefits of open energy system modelling in making resource assessments, including energy storage of varying durations.
Open energy system modelling is flexible, cost-efficient, transparent, and secure. It enables collective problem-solving and is essential for a just energy transition. Right now, we need it to ensure we build enough of the right technologies.
Picture Germany in 2035: the wind is still, the sun sets, and we depend on flexible technologies – most importantly, storage – to keep the lights on. If today’s planners rely only on opaque black-box models with hidden assumptions and calculations, there’s a real risk we’ll discover too late that essential technologies are missing, undersized, or in the wrong location. If this happens, the lights go out nationwide. Energy planning that hides assumptions behind proprietary walls is no longer fit for purpose. We need open models now.
Why energy storage gets ignored
Storage is too often overlooked. Why? First, it gets buried in opaque calculations. Second, models deem it “not cost-efficient enough” to build. This assessment is based on opaque assumptions, deeply embedded in every black-box model.
Try Premium for just $1
- Full premium access for the first month at only $1
- Converts to an annual rate after 30 days unless cancelled
- Cancel anytime during the trial period
Premium Benefits
- Expert industry analysis and interviews
- Digital access to PV Tech Power journal
- Exclusive event discounts
Or get the full Premium subscription right away
Or continue reading this article for free
Open models, by contrast, let us look under the hood. They show whether the assumptions are realistic, and how they drive the outcomes. Transparency allows manufacturers, investors, policymakers, transmission system operators (TSOs), and regulators to recognise when storage is critical and becomes cost-efficient, especially during multi-day ‘dark doldrums’ (aka ‘dunkelflaute’ in German).
Without that visibility, we risk underbuilding storage, overbuilding generation and paying the price later.
How open models solve the problem
While existing black-box energy planning has served us well so far, we at Open Energy Transition argue that open models must now become the standard in energy planning. Open models not only ensure transparency and trust: they also offer adaptability, security, and flexibility. Many models are available on the market, including PyPSA, GenX, OpenSwitch, OSeMOSYS, and many more – and they can be used and supported by multiple organisations, ensuring vendor independence.
Lessons from Germany
Recently, we conducted a study on multi-day storage (MDS) in Germany in collaboration with Form Energy. The goal: assess storage needs to reach near 100% clean power by 2035.
Many models fail to capture cost-optimal investments in MDS because they lack temporal detail. That’s why we used highly granular, multi-year climate data with annual optimisation. Here’s what the study found: Across 16 scenarios, factoring in gas phase-outs, delayed transmission, and gas price sensitivity, the results were clear: low-cost MDS has huge potential.
Up to 70GW could be deployed across modelled regions (31GW in Germany alone). MDS reduces curtailment, flattens electricity prices, cuts resource dependence, and helps achieve emission targets.
MDS, in the form of iron-air batteries (as produced by e.g. Form Energy), can lower system costs, strengthen grid support, and boost resilience during multi-day gaps. And Germany isn’t unique. The same open approach applies across Europe.
In fact, our open modelling projects already stretch beyond storage, from building insulation in European housing, to working on reproducing [European transmission system operator association] ENTSO-E’s Ten-Year Network Development Plan using the openly available and transparent Open-TYNDP repository.
Why openness matters
Could black box models have produced similar results? Probably. But open modelling did it cheaper, quicker, more transparently, and with lasting value. Organisations and companies such as Form Energy, a US-based multi-day storage technology company that OET has collaborated with, can now use the models moving forward because they’re open, freely available on GitHub, and reusable for future projects under MIT licenses.
Transparency is necessary in navigating today’s increasingly complex energy systems with many stakeholders, and it is independent of software vendors. Transparency in the code also means assumptions can be checked, outcomes tested, and findings reproduced. For the Germany study, PyPSA-Eur was used – a detailed open model dataset of the European energy system, which can be easily adapted to test new storage technologies within Europe or different regions around the world (with PyPSA-Earth).
But this isn’t just about cost or efficiency. Open models are adaptable, secure, and reusable. They can be reapplied to new contexts, enabling faster learning across countries and technologies. They’re also secure. Sensitive data can remain local, while open workflows ensure vulnerabilities are found and fixed by the community.
That’s more trustworthy than proprietary software, where security holes can remain hidden, and data can be exchanged with vendor servers without users realising it for months, years, or in the worst case, forever.
The bigger picture
Energy system modelling goes beyond forecasting; it opens a path to shaping the future, democratising insight, and allowing governments, utilities, industry, and communities to make decisions based on shared, testable evidence.
Energy storage, for example, cannot remain an afterthought. It is relevant to a resilient, reliable, net-zero system. Ignoring it risks blackouts, higher costs, and slower decarbonisation. Open models make the inherent value of energy storage visible to all.
Time to act
Open models aren’t futuristic gadgets or fads. They’re here, proven, and ready to use by policymakers, regulators, grid operators, and companies alike. They can work alongside proprietary software or replace it, saving on costly subscriptions while delivering comparable, high-quality insights.
The energy transition is upon us. To reach established decarbonisation goals and build resilient systems, planning must take the next step that many others have taken: move to open models. We are building with the ecosystem, and the question is no longer whether open models work, but why we’re not using them yet.
About the Authors
Charlotte Heikendorf (marketing lead), Daniel Rüdt (energy system modeller), Dr. Martha Maria Frysztacki (head of energy system modelling and co-founder) work at Open Energy Transition (OET), a registered nonprofit dedicated to accelerating the energy transition by tackling energy planning challenges.