Please note: 1. The english translations given here, including the name of the study, are unofficial. 2. An official english version of the main report is in progress. 3. None of the published material to date is open licensed — which means that diagrams and tables cannot be extracted and presented on a public forum such as this.
This post covers the published study “Pathways to a climate-neutral energy system — the German energy system transformation in the context of societal behavior” undertaken by Fraunhofer ISE (Sterchele et al 2020a). The study results were made public on 13 February 2020 and I attended the official presentation in Berlin, Germany.
Some background for readers not familiar with research institutes in Germany. The Fraunhofer ISE specializes in solar energy systems. It is located in Frieburg and is one of 72 Fraunhofer research institutes and research units that make up the Fraunhofer Society. Much of the academic research in Germany is structured this way with other notable associations being Helmholtz, Leibniz, and Max Planck.
The reported study investigates development pathways (sometimes known as trajectories) for the German energy system that reduce energy‑related CO2 emissions by variously 95% and 100% by 2050 (with one further 100% scenario targeting 2035). Achieving these goals for the energy sector is entirely feasible from a technical and systems perspective.
Notwithstanding, aggregate societal behavior is now a decisive factor. Detrimental behavior can restrict the technical solution space, exclude otherwise attractive pathways, increase cumulative expenditures, and impact negatively on other high‑level metrics. Whereas better aligned behavior can lead to considerably smaller and cheaper systems, with fewer downside consequences. Indeed, the German energiewende should be seen as much a social transformation as a technical transformation.
Social behavior can be made endogenous in energy system models with varying degrees of success (I have worked on three such attempts). The Fraunhofer ISE study instead introduces such behavior exogenously via scenarios that attempt to capture various aspects of societal behavior and attitudes. This study puts societal responses at the center of the analysis and that is a first to my knowledge.
Four main scenarios (table below) seek to capture various societal and political backstories and are evaluated using the objective of 95% decarbonization by 2050.
|Beharrung||inertia||strong resistance to the use of new technologies in the private realm|
|Inakzeptanz||resistant||strong resistance to the expansion of large infrastructure|
|Suffizienz||sufficient||marked changes in behavior that significantly reduce energy consumption|
|Referenz||reference||no additional boundary conditions that promote or impede the overarching objective|
Two secondary scenarios (table below) are also reported with their key properties as indicated. In the report, these are further qualified, for example, Referenz_100 becomes the reference plotline for 100% decarbonization and Suffizienz_2035 becomes the plotline supporting very rapid decarbonization.
|95%||2050||bulk of report|
|100%||2050||German government policy as of 18 December 2019|
|100%||2035||unrealistically high reliance on imported fuels|
Unfortunately the only mainstream 100% scenario reported is Referenz_100. Given the new official policy on decarbonization (see next section), hopefully future work will report on the “remaining” 100% scenarios.
A target year of 2035 is advocated by the Fridays for Future climate protest movement inspired by Greta Thunberg.
Official climate protection targets
At the beginning of the study, official German policy was 80–95% decarbonization by 2050, relative to 1990 levels (BMWi and BMU 2010).
Toward the end of the study, the German parliament passed the Federal Climate Protection Act (KSG) which shifted the 2050 target to 100% net reduction (German Parliament 2019). The new target entered into force on 18 December 2019, as follows (my translation):
[This Act] is based … on the commitment of the Federal Republic of Germany at the United Nations Climate Change Summit in New York on 23 September 2019 to pursue greenhouse gas neutrality by 2050 as a long-term goal. (§1.3)
The energy system model REMod — Regenerative Energien Modell — developed at Fraunhofer ISE, was used for the simulation and optimization of the scenarios. Previously, the model name had an appended “D” to indicates its scope was Germany: REMod‑D. The model is closed source and programmed in the Pascal language (which later became Delphi when Windows GUI programming support was added). The model is driven by the nonlinear, nonconvex, continuous system, heuristic solver CMA‑ES (covariance matrix adaptation evolution strategy), which makes it somewhat different from model frameworks that employ linear and mixed‑integer programming instead. Erlach et al (2018) describe the software in some detail.
REMod supports an hourly resolution but does not model electricity and gas transmission or AC load flow. The model seeks a pathway that offers the least financial cost amortized over the selected horizon.
REMod supports roll‑out constraints for technologies and mitigation measures more generally and learning curves as those technologies deploy (but neither feature yet for social change :). REMod also supports fleet vintage but does not actively retire or strand capital or compensate owners adversely affected by shifts in public policy.
REMod contains a differenciated building stock database and is able to apply quite well resolved building thermal performance retrofit measures in an optimized context. This level of detail is relatively rare in other modeling frameworks.
REMod supports international trade. Scenarios that rely on imported green liquid fuels and biomass to any degree are often contentious.
The OpenEnergy Platform provides a factsheet on REMod‑D.
For each scenario, the study reports the heuristically‑optimal pathway identified, via the following:
- annual evolution of the technology mix (structure) and supply mix (operations)
- annual evolution of energy‑related CO2 emissions, both per sector and total
And the following metrics at points along the entire transformation:
- cumulative expenditures
- estimated marginal cost of avoided CO2
In addition, various sector‑specific themes are highlighted, including the form, role, and propagation rate of contributions from:
- built environment mitigation — including existing building stock retrofit
- transformation of the traffic sector
- sector‑coupling, embedded storage, and other flexibility measures
- more specifically, green hydrogen from electrolysis
The model is run twice: first to determine the structural evolution of the system in question, and second, with that structure specified exogenously, to determine the costs of avoided CO2 over time.
It is hard to discuss exemplary results without being able to reuse the plots and tables contained in publications. The reader is instead referred to the original report (Sterchele et al 2020a) and supporting document (Sterchele et al 2020b).
Nor am I dwelling much on results because the 95% target that forms the bulk of this study is no longer official policy, neither is it especially relevant given full decarbonization was always the goal. Moreover, a 95% optimal system is unlikely to be a waypoint en route to a 100% optimal system.
The only scenario (2035 aside) also reported with 100% decarbonization is the reference scenario. Of note is the relatively small difference in cumulative expenditure between the two, some 30% more for full decarbonization (figure 28) — and certainly not nearly as much as some people opine.
What is rather evident however, is how expensive it is to work around societal inertia and resistance compared with acceptant change. Multipliers are in the order of 320% to 460% — or, in broad terms, an energiewende three or four‑fold more costly than it need be (figure 28). With the proviso that this result needs to be confirmed for 100% decarbonization.
The 2035 scenario resulted in very high reliance of imported biofuels, particularly green hydrogen. Yet it is difficult to imagine that this level of trade would eventuate in practice, particularly in a world where hopefully all countries are seeking to rapidly decarbonize their own economies.
This is a solid study, with clear research questions, understandable scenarios, well presented results, and readily accessible conclusions, both aggregate and specific. I guess a few points stand out for me:
- societal aspects can be included in analysis without having to characterize and calibrate the underlying individual and social dynamics, whether that be embedding attitudes, replicating decisions, propagating influence, or representing other causal processes
- with the change in official government policy to 100% decarbonization, the “missing” 100% scenarios need analyzing
- the difference in system characteristics between 95% and 100% decarbonization (for just the reference scenario) is not especially notable
- but the disparity between societal inertia and resistance and societal engagement is very significant
- transitions to zero‑carbon more rapid than 2050 will require that a social tipping point be crossed
- one model cannot do everything — and REMod is a good blend of temporal resolution, sector scope, and network simplicity for this kind of analytical role — that said, it remains to be seen how models that also embed AC load flow and span the European electricity grid perform in this space in the future
- the German energiewende is entirely achievable within the next three decades — whereas the consequences of not being carbon neutral within this timeframe are barely worth contemplating
The usual caveats about relying on closed models to inform public policy apply to this study. The practice of using closed policy analysis may well persist in Germany, but the European Commission is increasingly seeking policy transparency and that the trend will doubtless continue until “open by default” becomes the new benchmark for public policy analysis.
As always, please contact me directly if errors need correcting — otherwise feel free to comment below.
Erlach, Berit, Hans-Martin Henning, Christoph Kost, Andreas Palzer, and Cyril Stephanos (April 2018). Optimization model REMod-D: Materialien zur Analyse Sektorkopplung — Untersuchungen und Überlegungen zur Entwicklung eines integrierten Energiesystems [Optimization model REMod-D: materials for the sector coupling analysis: investigations and considerations for the development of an integrated energy system] (in German). Germany: acatech, Leopoldina, Akademienunion.
Federal Ministry of Economics and Technology (BMWi) and Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) (28 September 2010). Energy concept for an environmentally sound, reliable and affordable energy supply. Berlin, Germany: Federal Ministry of Economics and Technology (BMWi). Superseded policy. Archive copy. Policy database.
German Parliament (December 2019). Bundes-Klimaschutzgesetz (KSG) [German Federal Climate Protection Act (KSG)] (in German). Adopted on 12 December 2019 and entered into force on 18 December 2019. PDF.
Sterchele, Philip, Julian Brandes, Judith Heilig, Danien Wrede, Christoph Kost, Thomas Schlegl, Andreas Bett, and Hans-Martin Henning (February 2020). Wege zu einem Klimaneutralen Energiesysem: Die deutsche Energiewende im Kontext gesellschaftlicher Verhaltensweisen [Pathways to a climate-neutral energy system: the German energy system transformation in the context of societal behavior] (in German). Freiburg, Germany: Fraunhofer ISE.
Sterchele, Philip, Julian Brandes, Judith Heilig, Danien Wrede, Christoph Kost, Thomas Schlegl, Andreas Bett, and Hans-Martin Henning (February 2020b). Wege zu einem Klimaneutralen Energiesysem: Die deutsche Energiewende im Kontext gesellschaftlicher Verhaltensweisen — Anhang zur Studie [Pathways to a climate-neutral energy system: the German energy system transformation in the context of societal behavior — Annex to the study] (in German). Freiburg, Germany: Fraunhofer ISE. Supplementary material.
Sterchele, Philip (2019). Analysis of technology options to balance power generation from variable renewable energy: case study for the German energy system with the sector coupling model REMod. Düren, Germany: Shaker.
Note on open licensing
Occasionally I write for Wikipedia and my mailbox is full of traffic requesting that third‑party copyright holders reissue images — typically screenshots, plots, and diagrams — under Wikipedia‑compatible open licenses so I can add them to articles. In rare cases, I even adapt and redraw key diagrams to escape copyright. These various options are clearly time consuming and I don’t have the inclination to do so in this case. Instead I have asked four of the eight study authors and an institute press officer to consider reissuing their two PDFs under Creative Commons Attribution CC‑BY‑4.0 licenses in order to advance open science and to also allow reuse here. That request is only a few days old and I remain hopeful of a satisfactory outcome.