The Messages and Case Studies sections revealed a number of messages emerging from the various types of analysis carried out in REEEM. Although those messages can be relevant for both the scientific community and policy-makers, further actions must be taken in order to integrate and communicate. The objectives of the synthesis and outreach process are:

• Elicit integrated (i.e. cross-sectoral) messages that can help define the direction of policy making from a broader perspective.

• Communicate all messages (and the supporting material such as data and background information) in a way that promotes transparency, reproducibility, wide engagement and educational aspects.

• Be easily absorbed by future projects and processes, so that work undertaken here need not be repeated.

To fulfil the above objectives, the outcome of REEEM is shaped into the following products:

Synthesis of messages: An attempt to draw broader messages, emerging from the co-analysis of the messages presented in Section 3 for the EU as a whole and for the case studies. This action helps fulfil the first objective of the synthesis and outreach process.

REEEM Database: An open source database to store all the modelling outputs relevant to the integrated impact assessment and the underlying input data (as far as openly available). This product, as well as all the following ones, aim at fulfilling the second and the third objective of the process.

OSeMBE: The Open Source energy Model Base for the EU is an open-source, low-threshold model of the energy system of the EU28 + Norway and Switzerland built in the open source modelling framework OSeMOSYS [34]. It is used as stakeholder engagement model.

REEEMgame: A business game aimed at interactively taking experts and non-experts through key dynamics of transitions to a low-carbon energy system.

REEEMpathways: An online free and open platform showcasing the three REEEM pathways and the related messages defined in Section 3 and 4.1 with databased information - available in a digestible format.

Energy Modelling Platform for Europe (EMP-E): It is a platform consisting of a website, special issues of a leading journal and annual meeting was created by REEEM with inputs by DG R&I, DG Ener and DG JRC. Its aim is to provide a digest of energy models and insights for researchers and policy makers. It culminates in an annual event where energy modellers and policy-makers exchange ideas trough plenary discussions, workshops and poster sessions.

These products draw from what is called the REEEM “Integrated Framework”. That (described earlier) is a method derived to maximise the coherency and integration of a set of different tools and approaches calibrated to various levels by common pathway assumptions.

Figure 43 below depicts how the aforementioned products are linked. The data used and produced in the REEEM Integrated Framework is fed into the database. OSeMBE also takes data from and harmonises assumptions with the Integrated Framework. The data produced for and by OSeMBE (as well as the other models) is then also fed into the database. OSeMBE data is used in the development of the REEEMgame. Data and insights from all the models are used in the REEEMpathways tool. All the aforementioned tools and insights are then discussed, and data disseminated, at the EMP-E and particular ideas discussed there may then lead to their improvement.

Synthesis & outreach framework of the REEEM project Figure 43. Synthesis & outreach framework of the REEEM project.

Synthesis of messages

This sub-section describes the integrated messages emerging from the synthesis of the insights given in Section 3.

Integrated message 1: The impacts of the transition to a low carbon EU energy system are multi-dimensional and spatially varied

The high decarbonisation targets set by the European Union will have impacts on the development of the energy sector, and as a result on the environment, economies and societies in which that system operates. Those impacts though, are not expected to be distributed uniformly. They differ by Member State, sector of the economy and even regions within a country. Under possible future pathways, some groups will benefit while others may see detrimental effects. Firstly, in all pathways, economic growth (measured by GDP) is expected to be uneven across Member States, without necessarily being skewed towards a particular geographic area/group of countries. At the same time, when examining health impacts, central European countries such as Germany and Poland seem to benefit the most from the transition, as they see their Disability-Adjusted Life Year (DALY) losses decrease the most. Similarly, affordability (defined as the capacity of households to bear the energy expenditure to heat their properties) is another attribute that differs by Member State. The discrepancies in terms of affordability, as well as unemployment rate, may be even more pronounced when one looks at different regions within a country. The same may be said in terms of unintended environmental impacts. The study on the impact of high decarbonisation strategies on local ecosystems for Lithuania provides a clear case: strategies aiming at high shares of biomass in primary energy supply to curb GHGs emissions potentially open the path for intensive uses of such source. That results in intense mono-culture plantations reducing biodiversity. These in turn may cause irreversible damage to the ecosystem and, ultimately, to the economy of local communities. Part of that bio-diversity includes wild berries and mushrooms, that are prize pickings for locals. Their removal might result in strong opposition to low-carbon national strategies. The latter is a clear indication that national strategies and targets may have important effects if they are designed top-down without accounting for regional impacts. Moreover, even when GDP shows a considerable growth in a particular country, not every sector follows the same trajectory. Both in terms of gross added value to the national economy, as well as in terms of employment rate. Some sectors are expected to thrive (e.g. non-metallic minerals and vehicles), while industries such as coal will be negatively affected. Therefore, in order for a strategy to be thoroughly evaluated to explore differences in costs and benefits, impacts need to be assessed at different spatial and sectoral levels, with consideration given to a multi-criteria decisional approach.

The expected diverse impacts between and within Member States indicate risks but also opportunities in the transition to a low-carbon EU society. At a national level, as there will be “winners” and “losers” a - stronger union could emerge in an attempt to minimise the impacts. Policies supporting freedom of movement and re-training/re-focusing of skills within sectors will be needed. Thus, jobs lost in one location in one industry can be replaced by retrained workers from another. This will require brave EC intervention, creating an opportunity to advance faster in the two dimensions of the Energy Union: 1) Security, solidarity and trust and 2) Fully-integrated internal energy market. Without doing so will hamper the potential for equitable decarbonisation.

Integrated message 2: Broader engagement is imperative for deep decarbonisation

From the analysis carried out in REEEM, deep decarbonisation requires active contribution from a plethora of actors. Given the complexity of energy systems and the number of actors that can influence their course in different ways. As noted above decisions made only by central governments could lead to a high cost and diverse transitions with various negative impacts. The penetration of certain technologies (e.g. renewables) has to increase, which depends not only on government support, but also on R&D investments by businesses, funding schemes and mechanisms by certain funds, public acceptance and a shift in market structure and mindset. Citizens’ behaviour in particular and the choices they make will be a key factor in the evolution of the system. As noted earlier and later we identify that household appliance and technology choice is not a matter of economics and service only, but also familiarity and loyalty.

Further, interventions will need to cut across what is often considered as the energy sector, as well as its supporting industries. This is particularly the case for a system that might be dominated by variable renewables and batteries. These will require careful management. Concepts such as circular economy, more efficient logistics and recycling need to be regulated at all levels of the energy supply-consumption chains. This is especially for segments of the supply expected to rely heavily on rare materials. An example is the platinum group metals (PGM) which could be replacing platinum with palladium, while from rare earths an example would be substituting samarium for dysprosium.

Moreover, national government decisions should be made in conjunction with both sub- and transnational stakeholders. This is in order to account for different issues which are critical for the development of the system. For example, a national government needs to consider the system characteristics of neighbouring countries when a high load is expected to be transmitted through interconnectors as part of a broader energy security strategy. At the same time, regional development (e.g. district heating systems) may help reduce GHG emissions and thus, governments could engage more with local stakeholders to better understand what schemes would benefit certain projects. The same applies to the EC strategy which could benefit from delving deeper into national realities. This might explicitly exploit the strengths (and mitigate the weaknesses) of each Member State and adjust the goals accordingly. For instance, a common national, binding decarbonisation target could lead to countries that have a high potential reducing emissions to a degree that does not correspond to their capabilities while others with a lower potential could undergo a significantly high-cost transition. While a common regional target would allow those with high potential to deliver greater impact reducing the burden for those with lower potential.

Broader -and country sensitive- engagement may present the European Union with an opportunity to accelerate the transition to low-carbon societies. A higher level of engagement can be helped by science-informed discussions, open and transparent analytical tools and dissemination towards all interested actors.

Integrated message 3: The EU low-carbon transition is strongly linked to non-EU drivers

To be effective, the deep decarbonisation of the EU energy sector would need to take into account developments outside the EU. As revealed in the REEEM analysis, a number of technologies (e.g. lighting, renewables and electric vehicles) which are expected to play a catalytic role in the transition, rely heavily on critical materials. The latter are, for the most part, concentrated and produced in regions beyond the EU borders. Therefore, given the limited control that the EC may have over the exploitation of those materials, certain development plans -linked to the aforementioned technologies- could be put at risk. Judicious use of critical material resources at a global level is expected to be a determinant of global decarbonisation and thus, a greater level of cooperation and potentially regulation will need to be investigated to help reduce risk of material scarcity/overheated prices.

The development rates of technologies used in the EU energy system are, to some extent, linked to decarbonisation targets and supporting schemes in different parts of the world. Therefore, decarbonisation targets in the EU and outside may impact exports and consequently competitiveness in the EU and outside. Leveraging on the different market shares that regions have in different parts of the technology value chains could positively impact competitiveness and, ultimately, cooperation between regions.

Integrated message 4: There are non-trivial multidimensional path dependencies that cannot be ignored

Deep decarbonisation will lead us into path dependencies that will require active multidimensional intervention. Those dimensions can go across timing, sectors and within a sector:

• As mentioned in the previous messages, deep decarbonisation is expected to have significant impacts on the economy and society. But the impacts of these are often not necessarily in the hands of EU decision makers. Further, they will depend on the timing of the intervention. For example, the study on macroeconomic impacts in particular, illustrates how the fulfilment of the Paris Agreement could reduce GDP growth more compared to other pathways. Even though in those other pathways the ambition for curbing emissions is lower. That is because in the scenario examined the rest of the world acts to invest locally to reduce its emissions. In so doing it reduces its investment in Europe. In fact, it competes with Europe. That is because the scenario in question is accompanied by a roughly 10% higher consumption of critical materials (compared to the Coalition for a Low-carbon path pathway) as well as biomass and water. Thus, the timing of the intervention is important.

• At the same time, when the Paris Agreement target is achieved, there is an incremental increase in the relevant benefits such as lower health impacts. Interventions impact other sectors. Comparing the marginal cost to the marginal benefits of the transition to a significantly low-carbon pattern is not a straightforward process as it depends heavily on the perspective of each actor engaging in the decision-making. It is therefore critical, as mentioned in previous messages, to assess the pros and cons diligently. That is not only with regards to how the transition should materialise (i.e. which countries/regions/sectors to be affected the most) but also up to which level of decarbonisation the benefits are considered greater than the cost in other sectors.

• Lastly, there are important energy sector quirks. Importantly, the higher the need for electrification of sectors of the economy, the greater the need for low carbon baseload generation, or variable renewable energy technologies with flexibility. CCS, biomass and/or nuclear could represent the most affordable low-carbon options to reduce the need for flexibility, but they too come with risk. 100% decarbonisation of sectors will be very hard without negative emission technologies such as biomass coupled with CCS (BECCS) and the adoption of a net balance approach. For different reasons, the use of the above technologies (Biomass, CCS and Nuclear) has been debated in the EU as they have environmental, social and economic impacts that go beyond GHG emissions. Flexible generation options, include grid-connected storage, smart end-use technologies and increase of interconnections between Member States. They also come with risk. The appropriate mix between these options does not depend only upon cost and investment considerations, but also highly on security concerns, long-term purchase agreements and, not least, affordability of electricity prices. A larger base of comprehensive studies on the cross-sectoral and cross-scale implications of different mix of flexible and low-carbon generation options is needed to inform investments and policy decisions (such as those on capacity markets or support towards specific technological solutions). It is worth noting also that deeper changes to material and infrastructure systems, such as biomass building material, increased telecommuting etc. may hold much higher and lower cost mitigation potential than options that would ordinarily be included in a an energy policy makers remit.

Integrated message 5: Among the technology trends, energy efficiency and electrification of transportation are consistently confirmed as potential enablers of the decarbonisation

Some key technology trends emerge as potential drivers of deep decarbonisation, consistent with previous studies. Electrification of several energy supply chains is a robust finding in REEEM with supply allocated efficiently between decentralised and centralised sources, depending on the availability of primary and renewable resources and on the potential for cross-boundary transmission. Potential for electrification emerges in industry, through increased power-to-heat uses, and in the transportation sector.

Road transportation has high potential for decarbonisation and electrification. At the same time, the associated, negative, system-wide impacts are not trivial. As revealed by the study on health impacts and LCA, when it comes to particulate matter emissions (derived from road abrasion, tyres and break wear), electric vehicles are no more environmentally friendly than those that run on biofuels. On top of that, EVs are heavy reliant on critical materials which -as discussed in the current report- may have various implications. Consequently, if those impacts are accounted for and stricter regulations are set in place (with regards to either the use of critical materials or particulate emissions limits), the potential of EVs to curb emissions might be significantly increased. Recycling and efficient use of materials may represent a way to reduce impacts. An implication of this message, is that, expansion of public transportation and, in general, a shift across modes of transportation may lead to a decrease in the use of resources for meeting transportation service demands. These have to be further evaluated to better understand potential behavioural barriers from consumers. Surveys in three Member States have shown that consumers consistently tend to hold onto the same type of vehicle even when it does not represent the cost- or environment-optimal alternative. Support for information campaigns, eco-labelling and easy costing of choices could help win the inertia. Finally, further research in order for new technologies to emerge might be critical for the vehicle sector to overcome those issues.

In the residential sector, one low-hanging fruit for deep decarbonisation is represented by energy efficiency, especially through renovation of buildings. Technologically mature measures are available at low cost. Constraints to the pace of renovation seem to come mostly from the absence of business models and incomplete regulations.

Integrated message 6: Focusing on direct mitigation misses important leakage effects

Initial analysis indicates that meeting a target of 90% direct GHG mitigation might be achieved by simply pushing close to half of those emission elsewhere. Specifically, when the life cycle carbon footprint of technologies is examined (taking into account indirect emissions), the actual decarbonisation rate is lower than the one based on direct emissions. EU decarbonisation targets are at risk of incentivising indirect-carbon leakage towards other regions of the world, if global strategies towards the reduction of emissions along the entire value chains are not established. In addition to the local benefits, the overarching target of reducing GHG emissions is a global issue, and therefore one could examine whether the marginal cost of investing in reducing the emissions outside the EU is lower and the marginal, global benefits (as well as those for the EU economy) higher.

Integrated message 7: New energy security paradigms

Moving beyond the direct analysis of the REEEM integrated framework, various observations call for an urgent new look at security, beyond the traditional metrics of import vulnerability. According to the pathways we examine there are potential pictures of concern:

• There are the traditional risks associated with fossil fuels that will transform in value from supplying energy to flexibility services. Arguably these may result in a higher value (and thus vulnerability to a unit used).

• Supply security of new carriers, materials and technology will need to be undertaken. For example, biofuel imports may increase; RET technologies will be produced elsewhere and materials needed to produce or refurbish them will not be under the control of the EC.

• With an increase in extreme weather events key new energy sources are at risk. o On the supply side: By far the greatest concern lies with biofuels, where forest fires during heat waves can have enormous effect. While recent windstorm in Holland destroyed wind-turbines and hailstorms elsewhere damaged solar farms. o On the demand side: increase cooling demands required to keep power stations, industry and homes both cool and warm are stressing the system in ways unexpected. Yet we expect a rapid increase in the frequency and severity of hot and cold spells as well as rainy and dry spells. Each of which amplify demands on energy

• Finally, with increased flexibility to accommodate variable renewable energy technologies (rather than non-variable renewable energy technologies and nuclear) comes the need for increased ICT control and automation. That automation requires increased deployment of communication and processing power. With its increase comes the risk of cyber-attacks and security. Whether this is from a heavy, external attack, such as an electromagnetic pulse, or internal hacking, new vulnerabilities arise that must be carefully managed.

REEEM Database

In the REEEM project, a large group of modelling teams from different institutes has developed, used and linked different software with different programming languages and modelling paradigms. This results in a large variety of data structures. In the integrated assessment modelling framework of REEEM, data from different sectors are used and created, of different types, formats and with different levels of aggregation. In addition, as the REEEM pathways are iteratively revised (as described in Section 2), the input and output data of each model need to be revised several times throughout the project. This requires modellers to upload and download data to and from the database frequently. Finally, several models are soft-linked and some are iterated (such as NEWAGE and TIMES PanEU). Data versioning is crucial in order to ensure consistency in the inputs and outputs exchanged between the models and, ultimately, in the formulation of the REEEM pathways (see Section 2).

Thus, the project database needs to meet different requirements. Besides complying with basic data security and access regulations as described in the Data Management Plan (deliverable D6.6), the structure must be flexible and database usage should be as automated and comfortable for modellers as possible. This challenge was solved by developing scripts for importing and exporting data to and from the project database, customised for each modelling team according to their data structures and formats. All open support documentation from the different data processing and modelling activities is either available on GitHub or in the relevant open access publications.

The above complexities also led to challenges in the data classification and categorisation. These were solved by developing and implementing a flexible tagging system for model inputs and outputs. This allows for data in the database to be tagged with different tags, assigned by modellers and users according to their understanding of the meaning of the data. The data tagging adds a flexible top layer of data categorisation according to general definitions. It aims at making input and output data from different models and modelling teams more comparable. For instance, all cost variables or technical parameters can be accessed across the database. Besides the technical aspects, the legal aspects were considered as well. The project aims at publishing the data sets under open licenses. All openly licensed input and output data of the models and pathways (of the REEEMPathways tool in the REEEM database are publicly available also on the OpenEnergyPlatform (OEP) and can then be identified under the tag “REEEM”. The links between the REEEM Database and other REEEM activities as well as with the OEP are shown below in Figure 44. The database concept and the data structures are presented in great detail in the Technical Documentation of the REEEM Pathway Database (deliverable D6.5).

REEEM data management and dissemination Figure 44. REEEM data management and dissemination.

OSeMBE: Open Source energy Model Base for the EU

The Open Source energy MOdelling SYStem (OSeMOSYS) was used to build the Open Source energy Model Base for the European Union (OSeMBE). Within the scope of REEEM, OSeMBE is configured as a model of the electricity system of the EU28, with addition of Norway and Switzerland, covering a time span from current years until 2050. OSeMBE, its code base, its input data and metadata and all related documentation are available on REEEM.org as well as on the OSeMOSYS community’s website. Its factsheet (summary of key information for model comparison purposes) is also available on the Open Energy Platform, managed by the Open Energy Modelling Initiative according to best practices of open modelling science. The model is documented in deliverable D7.3 – Open Source Engagement Model, available here.

OSeMBE is purposefully and in accordance with the Grant Agreement of REEEM designed as a stakeholder engagement model. As such, it aims to illustrate to expert and non-expert stakeholders key dynamics of the transition to a low-carbon EU energy system featured in TIMES PanEU, however leaving out its detail and complexity. Its structure includes the 28 EU Member States, Norway and Switzerland as connected regions. Each region has a set of technologies and fuels available and can exchange electricity with its neighbours. The energy resources considered are: liquid biofuels, solid biomass, coal, geothermal energy, heavy fuel oil, natural gas, oil, oil shale, solar energy, uranium, waste, waves, and wind. The model distinguishes between domestic resources and imported resources. The resources can be converted to electricity by using combined cycle power plants (PPs), CHP PPs, fuel cells, gas cycle PPs, integrated gasification combined cycle PPs, internal combustion engines, nuclear reactors of generation II and III, solar photovoltaic, steam cycle PPs, and wind turbines. The model covers the years 2015 to 2050. Per year it has five seasons and one typical day per season represented by three time slices. To allow the analysis of the environmental impact of the power system, CO2 and particle matter 2.5 are considered. The latter was chosen after being identified as the most harmful emission by the EcoSense model. The key output metrics of OSeMBE in REEEM relate to economic, environmental and social impacts of the transition to a low-carbon EU electricity system. They are:

• Economic: Discounted investment per citizen, this indicator is available for entire Europe and per country, which allows to compare the investment needs among countries.

• Environmental: CO2 per citizen. The carbon intensity per citizen allow the comparison in between countries but also the comparison over time. Of interest is not only what the countries might reach in 2050 but also the different starting situations in 2015.

• Social: Levelised Cost of Electricity (LCOE) – do not indicate the final price. However, the LCOE gives a good indication on the cost for electricity generation which have an impact on the final price.

By focusing on the most relevant dynamics in the evolution of the energy system, OSeMBE aims to provide a starting point for policy makers, academia and the public to familiarise with energy systems investment modelling. It constitutes an open source research infrastructure which can serve as a showcase, but also as a starting point for further research. It has been and will be used at in Higher Education Institutions as a ground for 1) teaching kits on energy systems investment modelling, 2) research within Master and PhD theses, 3) flexible and light model base for large numbers of explorative scenario runs (spanning several ranges of uncertainties on future energy prices), 4) open source base for model comparisons at the Energy Modelling Platform for Europe and other European events and 5) model infrastructure to carry out regional or national analyses. For the latter case, scripts are under development within new funded actions to extract regional of national models out of OSeMBE, modify/improve them within the scope of group teaching activities and individual research and re-introduce them into the European model. In short, OSeMBE is not only an engagement model, but also a space for collaborative open research. As such, it fulfils the purpose to communicate the features of the modelling effort carried out in REEEM and facilitate the creation of impact.

As the model is smaller and flexible, more than 100 scenarios have been run during the REEEM project to provide the background data for the REEEMgame.

REEEMgame

The REEEMgame aims to support learning sessions with stakeholders to provide them with a low-threshold understanding of energy system dynamics. It shows key outcomes and disseminates the data behind a large number of scenarios run with the REEEM Open-source Engagement Model: OSeMBE.

In the current version, the user is assigned a specific "point-of-view" expressed as a set of economic, environmental and social preferences. The player mission is simple: make climate policy choices in 2020, 2030, and 2040 to maximise the weighted 2050-score for the assigned preferences. The decisions impact the score components as follows:

• Economic: Higher Gross Domestic Product (GDP) in 2050 is better

• Social: Cheaper access to energy for everyone in 2050 is better

• Environmental: Lower annual CO2 emissions in 2050 are better

Interface of the REEEMgame Figure 45. Interface of the REEEMgame.

The game aims to let the player interactively discover how policy decisions, investments in infrastructure and technology developments might affect the development of the European electricity sector in the transition to a low-carbon system. At three points in time (2020, 2030, 2040) levers may be changed by the player concerning the emission reduction pathway, the expected capital costs of Renewable Energy Technologies, and the upgrade of the trans-border electricity transmission between European countries, according to the 10-Year development plan by ENTSO-E.

The learning simulation has been run at stakeholder meetings and will also be made available to educational institutions and the general public online.

Stakeholders and partners within the REEEM project have contributed to the learning simulation throughout the development process by providing feedback on design, implementation and testing of the learning simulation.

The REEEMgame can be accessed through the project website.

REEEMpathways

Stakeholder engagement in the project builds largely on enabling tools and Work Package 7 has the function of disseminating the insights gained from the project, and to get feedback from stakeholders to improve the models and other material being developed in the project.

To reach this objective, an article-based open access online tool, REEEMpathways, has been developed to visualise the results/key messages derived from the integrated impact assessment modelling framework presented in Section 3 and enable stakeholder feedback and interaction.

The tool is populated by data stored in the REEEM Pathways Database and provides public access to modelling insights, input data and pathway assumptions from the project. The user interface is designed with an emphasis on organising and showing model data on charts. A number of developed features enhance usability and accessibility. Among these, the possibility of downloading the data underlying the charts.

The tool enables REEEM partners to publish and update their own articles providing multiple types of static and dynamic charts to choose from to visualise their own key messages and the data behind it.

REEEMpathways interface Figure 46. REEEMpathways interface.

Following the concept of the REEEM project, this allows policy makers and stakeholders to explore and compare possible decarbonisation pathways. This may assist in understanding the effects of and requirements for energy system changes.

The tool has been integrated with Twitter and this enables the public to discuss the results/key messages with REEEM partners and allows other modellers to contribute with their knowledge.

The tool can be accessed here.

Energy Modelling Platform for Europe (EMP-E)

Computational models can provide insights into potential decarbonisation pathways, create a ground for consultations and help roadmap long-term strategies. The modelling effort carried out in the REEEM project fulfils this purpose. Yet, it is one of many in Europe and it has limitations like all others. The strength of all these efforts lies in their complementarity, comparability, legacy and possibility to be taken further by future actions. Energy system modelling efforts across Europe are scattered, attempts towards inclusive and structured EU-wide fora bringing researchers and EU policy makers are scarce and transparency of modelling tools is in many cases limited.

With this view, the REEEM project created in 2017 the Energy Modelling Platform for Europe (EMP-E) as one of its deliverables. The Platform was created with inputs from the European Commission’s Directorate General Energy, Research and Innovation and Joint Research Centre.

The EMP-E aims to provide a peer-reviewed digest of models and policy insights to inform the transition towards a low-carbon European society, vis-à-vis the Energy Union and Climate objectives. It brings together researchers from across Europe and EU policy makers. It facilitates the transition towards new open and transparent modelling paradigms. The EMP-E constitutes the last ring of the chain leading in REEEM from the co-design of model-based assessment of decarbonisation pathways, to the documentation, simplification for expert and non-expert and finally sharing of outcomes and infrastructure. It does not only constitute a platform for sharing outcomes of the project, but rather for many more efforts to share their outcomes, thereby creating long-lasting impact.

The modelling platform culminates in a yearly event held at the Headquarters of Directorate General Research and Innovation (DG R&I), in Brussels. The first event took place on May 17-18th 2017 and was attended by around 80 participants, from research institutions across Europe, the European Commission and, to a lesser extent, industry. After the success of the first event, the REEEM project opened the organisation of the yearly events to the other projects funded under LCE21-2015, MEDEAS, REflex and SET-Nav, as part of a collaboration started by INEA. Attendance and participation grew and in its third edition the platform is co-organised by 9 funded projects. Its quick transformation into a collegial effort owned by research actions and promoted by the European Commission is a measure of the sustainability and impact of the Platform.

More impact resides in the Special Issue of Energy Strategy Reviews (Elsevier) ‘Energy Transition and Decarbonisation pathways for the EU’. Completed early 2019, it collects outcomes of and hot topics covered at the first EMP-E meeting. This Special Issue does not merely present a collection of articles covering a pre-defined topic. It provides a synthesis of highly complementary tools, practices, experiences and views to inform the research and innovation agenda for the European energy system. The full set of articles provides a holistic view of technical, cross-sectoral, financial, societal challenges of the transition to a low-carbon system. These challenges reflect research questions, highly relevant for national energy agencies and EU decision makers.

This knowledge repository is available not only as a number of open access articles, but also as a number of freely accessible online toolkits. Among these are toolkits developed within the European Commission, toolkits traditionally employed in scenario analyses for the EU, emerging open source toolkits and ground-breaking new, open databases.

A solid body of research infrastructure emerges, building on vast literature and experiences collected in the past few decades, and clearly moving towards the establishment of standards for: 1) creating open modelling tools and structuring open data sets, 2) make existing and widely-employed modelling tools transparent, 3) juxtaposing new tools to specifically analyse new challenges.

A large body of manuscripts was submitted by the participants of EMP-E 2017, synthesising decades of research from all over Europe on EU energy system transitions. The final outcome features 22 peer-reviewed articles, of which 10 with unlimited full open access and several presenting results of EU-funded actions.

The Special Issue is introduced by a preface from three Directorates General of the European Commission: Directorate General for Research and Innovation, Directorate General Energy and Directorate General Joint Research Centre.