Solph v0.5.3 has landed

Today, we released a new version of solph (solph 0.5.3 at PyPI, solph v0.5.3 at GitHub). It adds one important feature, the OffsetConverter now allows multiple inputs and multiple outputs. Still, it is mostly a maintenance release. As discussed in my thoughts on software maintenance, we are currently changing stuff “under the hood” to prepare for future changes. The decision to have a release was because we wanted to make sure that new installations do not have problems due to incompatible dependencies. As the latest versions of Pyomo and numpy are currently incompatible, we skipped a beta release. So in case you experience issues, please speak up.

Details on the new OffsetConverter can be found in the documentation. The component makes it possible to create a Converter with efficiencies depending on the part load condition. With the new formulation, the Flow with the NonConvex property is taken as reference, all other Flows are constrained with respect to this one. For consistence with “normal” Converters, the proportionality factor is called conversion_factor, while the offset to model part-load efficiencies is expressed as a normed_offset to facilitate investment optimisation.

Thoughts on Software Maintenance

Many projects focus on adding features, often neglecting measures to maintain software quality. One reason for this is financing, may it because new features can sell new licenses or because project funding is connected with them. On the long run, of course, easy-to-maintain code also facilitates adding new features.

Currently, we are rewriting stuff “under the hood” of solph to prepare for future additions, including time-series aggregation. Also, experimental features are removed if they do not mature. (This includes the approach for cellular energy systems, we recommend to use named tuples as labels instead.) Every now and then we try to change our code to eliminate deprecation warnings in time. The release of NumPy 2.0 shows that maintaining compatibility is not always easy. Although it is actually an evolutionary milestone, Pyomo first seemed to be hit between the eyes. In particular, it does not check compatibility of installed dependencies. Never version state to be compatible to numpy<2.0 only, but at least sometimes incompatible versions are installed by pip.

Thus, software relying on Pyomo – such as solph – currently looks broken when latest versions of NumPy are installed. The only option is to downgrade NumPy and wait for Pyomo to update. Not only because this is not the first time Pyomo effectively breaks solph without a warning, we are considering other back-ends. Alternatives also promise faster processing. But this is a big maintenance job, and hard to fund using the current funding scheme of research projects.

Save the date: 10th Anniversary Meeting in Oldenburg

At the end of this year, the open energy modelling framework will turn 10. The anniversary meeting will be held in Oldenburg from the 20th to the 22nd of November, 2024. The style will deviate from the standard developer meetings we typically have by the end of the year; it will be more like a user meeting.

To celebrate this special occasion, there will be three different locations, we will be visiting. Wednesday, we will be in the big seminar room of the DLR Institute of Networked Energy Systems, next to Campus Wechloy of Oldenburg University. This is the right place to give presentations for a bigger audience. For Thursday, we will move to the DLR site in down-town Oldenburg. We have several rooms reserved there to work in breakout groups. On Friday, we celebrate the developer part in the Mainframe Oldenburg, located next to Oldenburg central station. This place offers the perfect atmosphere for hands-on coding experiences.

More details will be collected at the corresponding Page GitHub:oemof/wiki/Meeting-2024.11:-10-years-of-oemof. We also have a preliminary agenda at the page already. Registration will open soon. To get to know each other, we agreed that everybody should be part of a contribution. This includes a wide range of possibilities:

  • Pitch (one static slide, one minute)
  • Presentation (five minutes up to 15 minutes)
  • Poster (A3 to A0), please do also give a pitch
  • Co-authorship (be named in a contribution of someone else)

To register, please write an email to Please tell your name, your institution, what kind of contribution you plan, and your nationality. (The latter is needed due to DLR regulations.)

2024 user meeting in Nordhausen: Thanks for joining!

The last user meeting was the biggest we ever had. We had very productive and inspiring discussions about using oemof (especially solph). Because of the size we gathered opinions in subgroups instead of making decisions about future developments in the plenary. Another reason for this also led to some other changes: Typically, we start with user presentations showing use-cases as well as open questions. This, however was scheduled as a point of the agenda of the parallel RET.Con. So, instead of gradually going to the core, we started with developer topics.

Continue reading “2024 user meeting in Nordhausen: Thanks for joining!”

solph v0.5.2: Next Network

Today, we had two new releases, 0.5.0 (GitHub, PyPI) and oemof.solph 0.5.2 (GitHub, PyPI). The release of the first includes a lot of refactoring and cleaning. The code should now be a lot easier to understand and to maintain. We now use explicit keyword arguments also for network, so typos will be easy to find. Secondly, there is a (still experimental) API to get Nodes by label. At last, we now officially support an API to add Flows between existing Nodes. Using this API in solph, the Nodes might e.g. be Buses:

Continue reading “solph v0.5.2: Next Network”

oemof user meeting 2024.02

From 7th to 9th of Februar 2024, we will have our annual user meeting, this time held in Nordhausen. It is set in the framework of the to the  7th Regenerative Energy Technology Conference (RET.Con) and the 20th anniversary celebrations of the course renewable energy technology (“Regenerative Energietechnik”) at the Nordhausen University of Applied Sciences.

With the program of the RET.Con being released, we now also created a (tentative) agenda for the oemof meeting 2024.02. In contrast to previous years, we will have the topics targeting more experienced users (like planning the development roadmap) at the first day. This allows to have topics also targeting beginners (e.g. the user presentations) open for visitors to the RET.Con.

If you plan to come, please register writing an email to, telling your name and (if applicable) your institution. We still have open slot for user presentations and tutorials. So if you want to present what you are doing using oemof or even share some hands-on experience, we will try to fit your contribution in. Note that it is okay to give a presentation in German. If possible, we prefer to have at least slides or spoken word in English. In the past, user presentations were also used for problem statements to find help on a particular topic and to have “reversed tutorials” asking for guidance. Both are options also for this user meeting.

As always, there are no fees for the oemof user meeting. You have to organise the trip (travel and accommodation) by yourself, meals are self-paid (and optional, you are free to organise something separate). So, don’t be confused by the RET.Con conference fee, this one does not apply for us.

2023-11 dev days: Retrospective

oemof developers discussing possible implementations

In the last days, we intensively discussed the next steps in the development of oemof. It was very intense and exciting to see other enthusiastic developers in person, drafting solutions at the white board and reviewing code in the presence of the persons who wrote it. We discussed long-term plans but also very particular problems, e.g. how to rewrite up-times in solph so that they are meaningful in models with time-steps of varying length. The most noticeable topics were mostly considering solph:

Continue reading “2023-11 dev days: Retrospective” v0.5.0a5 released

At the last user meeting, we decided that there should be more pre-releases. So, here we go: Today, there is a version “continuous clean-up” of ( oemof-network/v0.5.0a5, · PyPI). As the code name suggests, it is mostly a clean-up without adding new functionality. However, the code quality improved quite a lot and we have prepared the deletion of code that is unused or seems to be unnecessary. So, please check out this alpha release to tell if we are wrong.

Update: Deprecating the use of network.Source and others in favour of network.Node only makes sense when the latter is really part of the public API. so, we’re at v0.5.0 alpha 5 already.

oemof user meeting meets RET.Con

For next year’s user meeting, we take a special opportunity: It will be held from 7th to 9th of Februar 2024, partly in parallel to the  7th Regenerative Energy Technology Conference (RET.Con) in Nordhausen. The oemof user meeting will be in its established style, but we want to make it possible for attendees to the conference (which is held mostly in German) to visit presentations and tutorials given at the user meeting. Additionally, it is possible to add an entry for the proceedings of the conference.

This is also why we are announcing the user meeting already before the dev days have taken place: For the RET.Con, there is a deadline for abstract submission at the 30th of September 2023. Note that papers should be in German but presentations may also be in English. If you do not want to publish a paper, you can hand in a headline and a very brief summary for a talk until the 15th of November, so that an announcement can be made at the RET.Con. At last, of course you can ignore this early deadline and present something at the user meeting without having it announced at the conference.

If you want to want to submit something for the RET.Con via the oemof user meeting, please send an email to All emails to this address will also be forwarded to the organisers in Nordhausen.