6. Model interlinkages

Note

In brief — This chapter describes how OPEN-PROM is linked to companion models: openTEPES (power-sector detail), METEOR (spatial climate emulation), OMNIA-ENGAGE (circular economy), FTT:Heat (residential heating) and MAgPIE (land use and bioenergy). Of these, only the MAgPIE soft-link is operational in the repository today (task 7); the others are external links that are planned or under development within DIAMOND.

6.3. Circular economy representation with OMNIA-ENGAGE

Note

Status — external / planned. The OMNIA-ENGAGE link is a DIAMOND harmonisation exercise, not a coded OPEN-PROM workflow. Circular-economy strategies are represented inside OPEN-PROM through exogenous scenario inputs (activity levels, scrap shares, clinker-to-cement ratio); the model itself has no endogenous material-flow representation, and the aluminium and cement parts of the link are still in the design phase.

OPEN-PROM is a simulation-based energy-system model and does not currently include explicit representations of material flows, including the trade of feedstocks and waste. As such, it cannot endogenously model circular economy dynamics in terms of mass balances or material stock-flow interactions.

However, different circular economy strategies — such as material efficiency improvements, increased recycling rates, or reduced primary material demand — can be represented exogenously through scenario-specific assumptions on the activity level. For example, scenarios that represent high recycling rates or significant reductions in the use of a specific material can be captured by adjusting the input activity levels or material demands in relevant industrial processes. Moreover, the deployment of technologies with high scrap input (e.g. scrap-based electric arc furnaces) can be constrained or incentivised through additional constraints, allowing alignment with circularity-driven narratives. Subsidies for secondary production or penalties on energy-intensive primary routes can be used to accelerate the uptake of circular economy options if such policy signals are known or assumed in the scenario design.

In the iron and steel sector, the balance between primary production and secondary production (scrap-based steelmaking) is critical for circular economy pathways. In OPEN-PROM, this balance is represented as an external scenario input rather than calculated endogenously. Data on the share of scrap-based steel production can be directly retrieved from the OMNIA-ENGAGE model, ensuring alignment with circular economy strategies such as enhanced scrap collection, quality improvements for recycled steel, and increased recycling rates.

Similarly to iron and steel, in the aluminium sector the distinction between primary aluminium production (from bauxite refining and electrolysis) and secondary aluminium production (from remelted scrap) is another key lever for circular economy implementation. OPEN-PROM calibrates separate energy intensities and fuel mixes for primary and secondary aluminium production, with the share of secondary production also treated as an external scenario constraint that can be differentiated by country/region. This share can be directly informed by OMNIA-ENGAGE scenario assumptions, enabling the model to reflect scrap availability, recycling policies and circular economy strategies aimed at reducing the demand for new primary aluminium.

In the cement sector, circular economy practices will be captured through the clinker-to-cement ratio, which determines the share of supplementary cementitious materials (e.g. fly ash, slag) and directly influences the overall energy and emissions intensity of cement production. While material flows are not explicitly represented in OPEN-PROM, the clinker-to-cement ratio will be managed as an external scenario input and can be retrieved/calibrated to ensure alignment with OMNIA-ENGAGE model results for specific scenarios. This ensures that material efficiency improvements in the cement sector — such as increased blending of clinker substitutes — are consistently reflected in scenario analyses.

In general, material efficiency measures such as lightweighting in end-use sectors or extending product lifetimes are captured in the form of adjusted activity levels (production) in OPEN-PROM. This ensures that reductions in primary material demand driven by circular economy strategies are consistently integrated within the energy-system model, and OPEN-PROM can be used to assess the potential impacts of circular economy measures for national, European and global decarbonisation pathways.

At the moment the aluminium and cement sectors are in the design phase.

Enhanced representation. The harmonisation with the OMNIA-ENGAGE link, built upon the CGE structure of ENGAGE — which captures real material flows, trade patterns and the impacts of specific circular economy policies — will enable OPEN-PROM to reflect circularity implications through more coherent and data-driven input assumptions. This linkage, in the context of DIAMOND, allows OPEN-PROM to simulate the impacts of circular economy scenarios based on more sophisticated, science- and economy-based calculations, rather than relying solely on exogenous assumptions.

To support a coherent comparison exercise, OPEN-PROM will be run using the same regional definitions adopted in the OMNIA-ENGAGE framework. This alignment of regions ensures that differences in outcomes across models can be attributed to model structure and assumptions, rather than to inconsistencies in spatial aggregation. The comparison will focus initially on the industrial sector, where a key assumption for harmonisation is that, in the calibration year (base year), technological routes that are comparable across models will be disaggregated consistently by fuel use and technology type. This is essential because both models rely on initial-year data as the reference for future scenario projections, and aligning the initial fuel and technology shares is necessary to maintain comparability across scenarios. In fact, OPEN-PROM uses ENERDATA and IEA as the main source for calibrating fuel consumption in historical years, while OMNIA relies on the UN Energy Balances. The comparison will therefore involve aligning fuel use and technological shares for the base year across at least the following fuel categories: coal, natural gas, fuel oil, biomass and electricity, and for each industrial subsector (i.e. steel, cement and aluminium). These categories are also the main inputs to the techno-economic datasets used for modelling new low-carbon technologies in the industrial sector.

A critical element for comparison will be the techno-economic data associated with these technologies. When possible, the techno-economic data will be aligned at least for the industrial technologies described in OMNIA and OPEN-PROM that have a similar level of technological detail. This will allow a direct comparison of technology costs (including both CAPEX and OPEX) and performance assumptions across models, which is important because these costs are a key driver of technology uptake in alternative scenarios. Fuel prices are treated as exogenous in both OPEN-PROM and OMNIA-ENGAGE; therefore, comparing fuel price assumptions between the two models can help identify further sources of potential discrepancies in the results.

The link between OPEN-PROM and OMNIA-ENGAGE also extends beyond basic fuel and technology data, as OMNIA-ENGAGE provides key system-level drivers such as the energy-system configuration derived from the OMNIA model and the associated CO₂ emissions for comparison. Moreover, the GDP changes that directly affect material demand from ENGAGE will be used in OPEN-PROM. Lastly, the results from the OMNIA-ENGAGE framework will provide external scenario constraints on the share of primary and secondary production for steel and aluminium, reflecting raw-material constraints (e.g. scrap availability) and trade of commodities. These drivers are not explicitly represented in OPEN-PROM but are crucial for aligning the representation of circular economy practices and material efficiency measures in the two models.

OPEN-PROM will integrate the main scenario assumptions developed within OMNIA-ENGAGE by adopting key inputs and aligning core drivers for each specific scenario. Referring to examples of scenarios presented in D4.1, a high-level overview of how the insights and results deriving from the OMNIA-ENGAGE link will be integrated with OPEN-PROM improves the representation of circular economy. Energy-system configurations and material demand projections, including GDP-driven changes, will be used as external scenario constraints, allowing OPEN-PROM to replicate the broader system dynamics represented in OMNIA-ENGAGE.

In the case of a scenario based on a climate target, OPEN-PROM will integrate the regional decarbonisation pathways and detailed energy mix provided by OMNIA-ENGAGE. The shares of low-carbon technologies and the evolving energy-system structure will be adopted to ensure that OPEN-PROM reflects consistent decarbonisation strategies and their related CO₂ emissions and reduction in the scenario. Similarly, for an eventual scenario of increased material efficiency, OPEN-PROM will adopt the adjusted material demands — such as reduced steel and aluminium usage and associated decreases in scrap production — generated by linking OMNIA and ENGAGE. In this context, the shares of primary and secondary production for steel and aluminium, and the changes in sectoral production described in the model, will be updated based on OMNIA-ENGAGE outputs.