* The optimization is now performed using the ``pyomo=False`` setting in the :func:`pypsa.lopf.network_lopf`. This speeds up the solving process significantly and consumes much less memory. The inclusion of additional constraints were adjusted to the new implementation. They are all passed to the :func:`network_lopf` function via the ``extra_functionality`` argument. The rule ``trace_solve_network`` was integrated into the rule :mod:`solve_network` and can be activated via configuration with ``solving: options: track_iterations: true``. The charging and discharging capacities of batteries modelled as store-link combination are now coupled (`#116 <https://github.com/PyPSA/pypsa-eur/pull/116>`_).
* Removed the `id` column for custom power plants in `data/custom_powerplants.csv` to avoid custom power plants with conflicting ids getting attached to the wrong bus (`#131 <https://github.com/PyPSA/pypsa-eur/pull/131>`_).
*``snakemake`` rules for retrieving cutouts and the natura raster can now be disabled independently from their respective rules to build them; via ``config.*yaml`` (`#136 <https://github.com/PyPSA/pypsa-eur/pull/136>`_).
* Documentation on installation, workflows and configuration settings is now available online at `pypsa-eur.readthedocs.io <pypsa-eur.readthedocs.io>`_ (`#65 <https://github.com/PyPSA/pypsa-eur/pull/65>`_).
* The ``conda`` environment files were updated and extended (`#81 <https://github.com/PyPSA/pypsa-eur/pull/81>`_).
* The power plant database was updated with extensive filtering options via ``pandas.query`` functionality (`#84 <https://github.com/PyPSA/pypsa-eur/pull/84>`_ and `#94 <https://github.com/PyPSA/pypsa-eur/pull/94>`_).
* Continuous integration testing with `Travis CI <https://travis-ci.org>`_ is now included for Linux, Mac and Windows (`#82 <https://github.com/PyPSA/pypsa-eur/pull/82>`_).
* Data dependencies are now retrieved directly from within the snakemake workflow (`#86 <https://github.com/PyPSA/pypsa-eur/pull/86>`_).
* Emission prices can be added to marginal costs of generators through the keyworks ``Ep`` in the ``{opts}`` wildcard (`#100 <https://github.com/PyPSA/pypsa-eur/pull/100>`_).
* An option is introduced to add extendable nuclear power plants to the network (`#98 <https://github.com/PyPSA/pypsa-eur/pull/98>`_).
* Focus weights can now be specified for particular countries for the network clustering, which allows to set a proportion of the total number of clusters for particular countries (`#87 <https://github.com/PyPSA/pypsa-eur/pull/87>`_).
* A new rule :mod:`add_extra_components` allows to add additional components to the network only after clustering. It is thereby possible to model storage units (e.g. battery and hydrogen) in more detail via a combination of ``Store``, ``Link`` and ``Bus`` elements (`#97 <https://github.com/PyPSA/pypsa-eur/pull/97>`_).
* Hydrogen pipelines (including cost assumptions) can now be added alongside clustered network connections in the rule :mod:`add_extra_components` . Set ``electricity: extendable_carriers: Link: [H2 pipeline]`` and ensure hydrogen storage is modelled as a ``Store``. This is a first simplified stage (`#108 <https://github.com/PyPSA/pypsa-eur/pull/108>`_).
* Logfiles for all rules of the ``snakemake`` workflow are now written in the folder ``log/`` (`#102 <https://github.com/PyPSA/pypsa-eur/pull/102>`_).
* The new function ``_helpers.mock_snakemake`` creates a ``snakemake`` object which mimics the actual ``snakemake`` object produced by workflow by parsing the ``Snakefile`` and setting all paths for inputs, outputs, and logs. This allows running all scripts within a (I)python terminal (or just by calling ``python <script-name>``) and thereby facilitates developing and debugging scripts significantly (`#107 <https://github.com/PyPSA/pypsa-eur/pull/107>`_).
* Upload pre-built networks to `zenodo data repository <https://doi.org/10.5281/zenodo.3601882>`_ with `CC BY 4.0 <https://creativecommons.org/licenses/by/4.0/>`_ license.
* Send announcement on the `PyPSA and PyPSA-Eur mailing list <https://groups.google.com/forum/#!forum/pypsa>`_.
