The Ariadne project was an evidence‑based assessment aimed at providing German decision makers with a stronger scientific foundation for shaping the national energy transition. Its overarching objectives were to stimulate learning processes between policy and science, to analyse and develop measures and policy pathways, and to integrate a system perspective with detailed sectoral knowledge. The project ran from 2020 until August 2023 and was funded by the Federal Ministry of Education and Research under grant number 03SFK5F0. The Potsdam Institute for Climate Impact Research (PIK) coordinated the overall consortium, while the Öko‑Institut contributed exclusively to work package 8 (AP 8), the sectoral focus analysis on the heating transition, which was coordinated by the Fraunhofer Institute for Solar Energy Systems (ISE). Other partners in AP 8 were the Institute for Energy Research (IER), the German Institute for Economic Research (RWI), the Institute of Urban Development (IW Köln), the Munich Center for Climate and Environmental Research (MCC), the Institute for Climate and Energy Research (IKEM), PIK itself, and adelphi.

Within AP 8 the heating‑transition focus was divided into nine tasks; the Öko‑Institut carried out four of them. Its main technical contributions were the identification and description of policy instruments for building‑energy efficiency, the evaluation of these instruments in terms of robustness and goal attainment, and the development of alternative policy options. The instruments examined covered regulatory reforms, fiscal measures such as tax incentives and subsidies, information and advisory services, technology‑specific actions, and planning approaches, with a particular emphasis on municipal heat planning. Each instrument was quantified and its expected impact was split into three time horizons—short, medium, and long term—allowing a clear assessment of immediate and future effects. The analysis also addressed the modernization levy and the landlord‑tenant dilemma, providing insights into how financial mechanisms can be aligned with equity concerns. Stakeholder participation was systematically incorporated, ensuring that the assessment reflected the perspectives of actors across the sector.

The project followed a two‑phase methodology aligned with the Green Book and White Book process of the consortium. In the first phase a comprehensive inventory of relevant measures and instruments was compiled, described in detail, and their effects quantified. The second phase involved a deeper dive into selected topics, refining the design of measures and exploring adaptation options. The Öko‑Institut’s work on municipal heat planning produced a set of actionable recommendations for local authorities, while its analysis of the modernization levy offered a framework for balancing investment needs with tenant protection. The evaluation of policy robustness identified gaps and synergies, informing the design of more resilient policy mixes.

Collaboration within the consortium was coordinated through biweekly “jour‑fixe” meetings for AP 8 and regular consortium gatherings, which were largely held online due to the COVID‑19 pandemic. These meetings ensured alignment across work packages and facilitated the integration of sectoral findings into the broader Ariadne assessment. The Öko‑Institut’s contributions were disseminated through a series of publications and planned further outreach activities, aiming to influence policy development and support the German energy transition. The final report, published in 2023, documents the technical outcomes, the collaborative process, and the anticipated impact of the findings on future policy design.