diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
new file mode 100644
index 00000000..a3268243
--- /dev/null
+++ b/.github/workflows/ci.yaml
@@ -0,0 +1,47 @@
+# SPDX-FileCopyrightText: : 2021 The PyPSA-Eur Authors
+#
+# SPDX-License-Identifier: CC0-1.0
+
+name: CI
+
+on: [push]
+
+jobs:
+  build:
+
+    runs-on: ${{ matrix.os }}
+    strategy:
+      max-parallel: 5
+      matrix:
+        os:
+        - ubuntu-latest
+        - macos-latest
+        - windows-latest
+
+    defaults:
+      run:
+        shell: bash -l {0}
+
+    steps:
+
+    - uses: actions/checkout@v2
+
+    - name: Setup Miniconda
+      uses: conda-incubator/setup-miniconda@v2.1.1 
+      with: # checks out environment 'test' by default
+          mamba-version: "*"
+          channels: conda-forge,defaults
+          channel-priority: true
+
+    - name: Install dependencies  
+      run: |
+        echo -ne "url: ${CDSAPI_URL}\nkey: ${CDSAPI_TOKEN}\n" > ~/.cdsapirc
+        echo -e "  - glpk\n  - ipopt<3.13.3" >> envs/environment.yaml
+        mamba env update -f envs/environment.yaml --name test
+        
+    - name: Test snakemake workflow
+      run: |
+        conda list
+        cp test/config.test1.yaml config.yaml
+        snakemake --cores all solve_all_networks
+        rm -rf resources/*.nc resources/*.geojson resources/*.h5 networks results
diff --git a/.travis.yml b/.travis.yml
deleted file mode 100644
index 79826a64..00000000
--- a/.travis.yml
+++ /dev/null
@@ -1,39 +0,0 @@
-# SPDX-FileCopyrightText: : 2017-2020 The PyPSA-Eur Authors
-#
-# SPDX-License-Identifier: GPL-3.0-or-later
-
-branches:
-  only:
-  - master
-
-os:
-  - windows
-  - linux
-  - osx
-
-language: bash
-
-before_install:
-  # install conda
-  - wget https://raw.githubusercontent.com/trichter/conda4travis/latest/conda4travis.sh -O conda4travis.sh
-  - source conda4travis.sh
-
-  # install conda environment
-  - conda install -c conda-forge mamba
-  - mamba env create -f ./envs/environment.yaml
-  - conda activate pypsa-eur
-
-  # install open-source solver
-  - mamba install -c conda-forge glpk ipopt'<3.13.3'
-
-  # list packages for easier debugging
-  - conda list
-
-before_script:
-  - 'echo -ne "url: ${CDSAPI_URL}\nkey: ${CDSAPI_TOKEN}\n" > ~/.cdsapirc'
-
-script:
-  - cp ./test/config.test1.yaml ./config.yaml
-  - snakemake -j all solve_all_networks
-  - rm -rf resources/*.nc resources/*.geojson resources/*.h5 networks results
-  # could repeat for more configurations in future
diff --git a/README.md b/README.md
index dc6b4791..15f979a7 100644
--- a/README.md
+++ b/README.md
@@ -4,7 +4,7 @@ SPDX-License-Identifier: CC-BY-4.0
 -->
 
 ![GitHub release (latest by date including pre-releases)](https://img.shields.io/github/v/release/pypsa/pypsa-eur?include_prereleases)
-[![Build Status](https://travis-ci.org/PyPSA/pypsa-eur.svg?branch=master)](https://travis-ci.org/PyPSA/pypsa-eur)
+[![Build Status](https://github.com/pypsa/pypsa-eur/actions/workflows/ci.yaml/badge.svg)](https://github.com/PyPSA/pypsa-eur/actions)
 [![Documentation](https://readthedocs.org/projects/pypsa-eur/badge/?version=latest)](https://pypsa-eur.readthedocs.io/en/latest/?badge=latest)
 ![Size](https://img.shields.io/github/repo-size/pypsa/pypsa-eur)
 [![Zenodo](https://zenodo.org/badge/DOI/10.5281/zenodo.3520874.svg)](https://doi.org/10.5281/zenodo.3520874)
diff --git a/config.default.yaml b/config.default.yaml
index 51721729..27ca63d0 100755
--- a/config.default.yaml
+++ b/config.default.yaml
@@ -40,7 +40,7 @@ enable:
 electricity:
   voltages: [220., 300., 380.]
   co2limit: 7.75e+7 # 0.05 * 3.1e9*0.5
-  co2base: 1.487e9
+  co2base: 1.487e+9
   agg_p_nom_limits: data/agg_p_nom_minmax.csv
 
   extendable_carriers:
diff --git a/doc/index.rst b/doc/index.rst
index 02b02ce2..e7dabdf4 100644
--- a/doc/index.rst
+++ b/doc/index.rst
@@ -9,8 +9,8 @@ PyPSA-Eur: An Open Optimisation Model of the European Transmission System
 .. image:: https://img.shields.io/github/v/release/pypsa/pypsa-eur?include_prereleases
     :alt: GitHub release (latest by date including pre-releases)
 
-.. image:: https://travis-ci.org/PyPSA/pypsa-eur.svg?branch=master
-    :target: https://travis-ci.org/PyPSA/pypsa-eur
+.. image:: https://github.com/pypsa/pypsa-eur/actions/workflows/ci.yaml/badge.svg
+    :target: https://github.com/PyPSA/pypsa-eur/actions
 
 .. image:: https://readthedocs.org/projects/pypsa-eur/badge/?version=latest
     :target: https://pypsa-eur.readthedocs.io/en/latest/?badge=latest
diff --git a/doc/release_notes.rst b/doc/release_notes.rst
index 5330128c..9f171981 100644
--- a/doc/release_notes.rst
+++ b/doc/release_notes.rst
@@ -1,5 +1,5 @@
 ..
-  SPDX-FileCopyrightText: 2019-2020 The PyPSA-Eur Authors
+  SPDX-FileCopyrightText: 2019-2021 The PyPSA-Eur Authors
 
   SPDX-License-Identifier: CC-BY-4.0
 
@@ -20,6 +20,11 @@ Upcoming Release
 * Add option to include marginal costs of links representing fuel cells, electrolysis, and battery inverters 
   [`#232 <https://github.com/PyPSA/pypsa-eur/pull/232>`_].
 * Add option to pre-aggregate nodes without power injections (positive or negative, i.e. generation or demand) to electrically closest nodes or neighbors in ``simplify_network``. Defaults to ``False``. This affects nodes that are no substations or have no offshore connection.
+* Fix: Add escape in :mod:`base_network` if all TYNDP links are already contained in the network [`#246 <https://github.com/PyPSA/pypsa-eur/pull/246>`_].
+* Bugfix in :mod:`solve_operations_network`: optimised capacities are now fixed for all extendable links, not only HVDC links [`#244 <https://github.com/PyPSA/pypsa-eur/pull/244>`_].
+* The ``focus_weights`` are now also considered when pre-clustering in the :mod:`simplify_network` rule [`#241 <https://github.com/PyPSA/pypsa-eur/pull/241>`_].
+* Continuous integration testing switches to Github Actions from Travis CI [`#252 <https://github.com/PyPSA/pypsa-eur/pull/252>`_].
+* Bugfix in :mod:`build_renewable_profile` where offshore wind profiles could no longer be created [`#249 <https://github.com/PyPSA/pypsa-eur/pull/249>`_].
 
 PyPSA-Eur 0.3.0 (7th December 2020)
 ==================================
@@ -45,6 +50,7 @@ Using the ``{opts}`` wildcard for scenarios:
   uses the `tsam <https://tsam.readthedocs.io/en/latest/index.html>`_ package
   [`#186 <https://github.com/PyPSA/pypsa-eur/pull/186>`_].
 
+
 More OPSD integration:
 
 * Add renewable power plants from `OPSD <https://data.open-power-system-data.org/renewable_power_plants/2020-08-25>`_ to the network for specified technologies.
diff --git a/envs/environment.yaml b/envs/environment.yaml
index 790aec26..3d0a3400 100644
--- a/envs/environment.yaml
+++ b/envs/environment.yaml
@@ -13,13 +13,12 @@ dependencies:
   - mamba # esp for windows build
 
   - pypsa>=0.17.1 
-  - atlite>=0.2.2
+  - atlite>=0.2.4
   - dask<=2021.3.1 # until https://github.com/dask/dask/issues/7583 is solved
 
   # Dependencies of the workflow itself
   - xlrd
   - openpyxl
-  - scikit-learn
   - pycountry
   - seaborn
   - snakemake-minimal
@@ -28,8 +27,17 @@ dependencies:
   - pytables
   - lxml
   - powerplantmatching>=0.4.8
-  - numpy<=1.19.0 # otherwise macos fails
-
+  - numpy<=1.19 # until new PyPSA after 27-06-21
+  - pandas
+  - geopandas
+  - xarray
+  - netcdf4
+  - networkx
+  - scipy
+  - shapely
+  - progressbar2
+  - pyomo
+  - matplotlib
 
   # Keep in conda environment when calling ipython
   - ipython
@@ -37,6 +45,13 @@ dependencies:
   # GIS dependencies:
   - cartopy
   - descartes
+  - rasterio
+
+  # PyPSA-Eur-Sec Dependencies
+  - geopy
+  - tqdm
+  - pytz
+  - country_converter
 
   - pip:
     - vresutils==0.3.1
diff --git a/scripts/_helpers.py b/scripts/_helpers.py
index 807c439f..996baf73 100644
--- a/scripts/_helpers.py
+++ b/scripts/_helpers.py
@@ -156,7 +156,6 @@ def aggregate_p_curtailed(n):
     ])
 
 def aggregate_costs(n, flatten=False, opts=None, existing_only=False):
-    from six import iterkeys, itervalues
 
     components = dict(Link=("p_nom", "p0"),
                       Generator=("p_nom", "p"),
@@ -167,8 +166,8 @@ def aggregate_costs(n, flatten=False, opts=None, existing_only=False):
 
     costs = {}
     for c, (p_nom, p_attr) in zip(
-        n.iterate_components(iterkeys(components), skip_empty=False),
-        itervalues(components)
+        n.iterate_components(components.keys(), skip_empty=False),
+        components.values()
     ):
         if c.df.empty: continue
         if not existing_only: p_nom += "_opt"
diff --git a/scripts/base_network.py b/scripts/base_network.py
index e43c4baf..778f8dc4 100644
--- a/scripts/base_network.py
+++ b/scripts/base_network.py
@@ -74,7 +74,6 @@ import scipy as sp
 import networkx as nx
 
 from scipy.sparse import csgraph
-from six import iteritems
 from itertools import product
 
 from shapely.geometry import Point, LineString
@@ -213,6 +212,7 @@ def _add_links_from_tyndp(buses, links):
     if links_tyndp["j"].notnull().any():
         logger.info("TYNDP links already in the dataset (skipping): " + ", ".join(links_tyndp.loc[links_tyndp["j"].notnull(), "Name"]))
         links_tyndp = links_tyndp.loc[links_tyndp["j"].isnull()]
+        if links_tyndp.empty: return buses, links
 
     tree = sp.spatial.KDTree(buses[['x', 'y']])
     _, ind0 = tree.query(links_tyndp[["x1", "y1"]])
@@ -268,13 +268,13 @@ def _apply_parameter_corrections(n):
 
     if corrections is None: return
 
-    for component, attrs in iteritems(corrections):
+    for component, attrs in corrections.items():
         df = n.df(component)
         oid = _get_oid(df)
         if attrs is None: continue
 
-        for attr, repls in iteritems(attrs):
-            for i, r in iteritems(repls):
+        for attr, repls in attrs.items():
+            for i, r in repls.items():
                 if i == 'oid':
                     r = oid.map(repls["oid"]).dropna()
                 elif i == 'index':
diff --git a/scripts/build_renewable_profiles.py b/scripts/build_renewable_profiles.py
index f7e1bc7f..111eb772 100644
--- a/scripts/build_renewable_profiles.py
+++ b/scripts/build_renewable_profiles.py
@@ -183,6 +183,7 @@ import progressbar as pgb
 import geopandas as gpd
 import xarray as xr
 import numpy as np
+import functools
 import atlite
 import logging
 from pypsa.geo import haversine
@@ -235,7 +236,10 @@ if __name__ == '__main__':
         excluder.add_raster(paths.corine, codes=codes, buffer=buffer, crs=3035)
 
     if "max_depth" in config:
-        func = lambda v: v <= -config['max_depth']
+        # lambda not supported for atlite + multiprocessing
+        # use named function np.greater with partially frozen argument instead
+        # and exclude areas where: -max_depth > grid cell depth
+        func = functools.partial(np.greater,-config['max_depth'])
         excluder.add_raster(paths.gebco, codes=func, crs=4236, nodata=-1000)
 
     if 'min_shore_distance' in config:
diff --git a/scripts/build_shapes.py b/scripts/build_shapes.py
index 2651837b..96d4a60f 100644
--- a/scripts/build_shapes.py
+++ b/scripts/build_shapes.py
@@ -73,7 +73,7 @@ from _helpers import configure_logging
 import os
 import numpy as np
 from operator import attrgetter
-from six.moves import reduce
+from functools import reduce
 from itertools import takewhile
 
 import pandas as pd
diff --git a/scripts/cluster_network.py b/scripts/cluster_network.py
index a01f682f..8356f83b 100644
--- a/scripts/cluster_network.py
+++ b/scripts/cluster_network.py
@@ -135,7 +135,7 @@ import pyomo.environ as po
 import matplotlib.pyplot as plt
 import seaborn as sns
 
-from six.moves import reduce
+from functools import reduce
 
 from pypsa.networkclustering import (busmap_by_kmeans, busmap_by_spectral_clustering,
                                      _make_consense, get_clustering_from_busmap)
diff --git a/scripts/make_summary.py b/scripts/make_summary.py
index 4d3e9ee5..f815d5f0 100644
--- a/scripts/make_summary.py
+++ b/scripts/make_summary.py
@@ -60,7 +60,6 @@ import os
 import pypsa
 import pandas as pd
 
-from six import iteritems
 from add_electricity import load_costs, update_transmission_costs
 
 idx = pd.IndexSlice
@@ -386,7 +385,7 @@ def make_summaries(networks_dict, country='all'):
     for output in outputs:
         dfs[output] = pd.DataFrame(columns=columns,dtype=float)
 
-    for label, filename in iteritems(networks_dict):
+    for label, filename in networks_dict.items():
         print(label, filename)
         if not os.path.exists(filename):
             print("does not exist!!")
@@ -417,7 +416,7 @@ def make_summaries(networks_dict, country='all'):
 def to_csv(dfs):
     dir = snakemake.output[0]
     os.makedirs(dir, exist_ok=True)
-    for key, df in iteritems(dfs):
+    for key, df in dfs.items():
         df.to_csv(os.path.join(dir, f"{key}.csv"))
 
 
diff --git a/scripts/plot_network.py b/scripts/plot_network.py
index e55b5de0..810f6284 100755
--- a/scripts/plot_network.py
+++ b/scripts/plot_network.py
@@ -25,7 +25,6 @@ from _helpers import (load_network_for_plots, aggregate_p, aggregate_costs,
 
 import pandas as pd
 import numpy as np
-from six.moves import zip
 
 import cartopy.crs as ccrs
 import matplotlib.pyplot as plt
diff --git a/scripts/prepare_network.py b/scripts/prepare_network.py
index fc5c6e77..4caa5703 100755
--- a/scripts/prepare_network.py
+++ b/scripts/prepare_network.py
@@ -62,7 +62,6 @@ import re
 import pypsa
 import numpy as np
 import pandas as pd
-from six import iteritems
 
 from add_electricity import load_costs, update_transmission_costs
 
@@ -145,7 +144,7 @@ def average_every_nhours(n, offset):
 
     for c in n.iterate_components():
         pnl = getattr(m, c.list_name+"_t")
-        for k, df in iteritems(c.pnl):
+        for k, df in c.pnl.items():
             if not df.empty:
                 pnl[k] = df.resample(offset).mean()
 
diff --git a/scripts/simplify_network.py b/scripts/simplify_network.py
index 309e94ff..ea27c7ad 100644
--- a/scripts/simplify_network.py
+++ b/scripts/simplify_network.py
@@ -93,8 +93,7 @@ import numpy as np
 import scipy as sp
 from scipy.sparse.csgraph import connected_components, dijkstra
 
-from six import iteritems
-from six.moves import reduce
+from functools import reduce
 
 import pypsa
 from pypsa.io import import_components_from_dataframe, import_series_from_dataframe
@@ -193,7 +192,7 @@ def _aggregate_and_move_components(n, busmap, connection_costs_to_bus, aggregate
         n.mremove(c, n.df(c).index)
 
         import_components_from_dataframe(n, df, c)
-        for attr, df in iteritems(pnl):
+        for attr, df in pnl.items():
             if not df.empty:
                 import_series_from_dataframe(n, df, c, attr)
 
@@ -237,7 +236,7 @@ def simplify_links(n):
                       if len(G.adj[m]) > 2 or (set(G.adj[m]) - nodes)}
 
         for u in supernodes:
-            for m, ls in iteritems(G.adj[u]):
+            for m, ls in G.adj[u].items():
                 if m not in nodes or m in seen: continue
 
                 buses = [u, m]
@@ -245,7 +244,7 @@ def simplify_links(n):
 
                 while m not in (supernodes | seen):
                     seen.add(m)
-                    for m2, ls in iteritems(G.adj[m]):
+                    for m2, ls in G.adj[m].items():
                         if m2 in seen or m2 == u: continue
                         buses.append(m2)
                         links.append(list(ls)) # [name for name in ls])
@@ -365,6 +364,8 @@ def aggregate_to_substations(n, buses_i=None):
 def cluster(n, n_clusters):
     logger.info(f"Clustering to {n_clusters} buses")
 
+    focus_weights = snakemake.config.get('focus_weights', None)
+    
     renewable_carriers = pd.Index([tech
                                     for tech in n.generators.carrier.unique()
                                     if tech.split('-', 2)[0] in snakemake.config['renewable']])
@@ -378,7 +379,8 @@ def cluster(n, n_clusters):
                                             for tech in renewable_carriers]))
                         if len(renewable_carriers) > 0 else 'conservative')
     clustering = clustering_for_n_clusters(n, n_clusters, custom_busmap=False, potential_mode=potential_mode,
-                                           solver_name=snakemake.config['solving']['solver']['name'])
+                                           solver_name=snakemake.config['solving']['solver']['name'],
+                                           focus_weights=focus_weights)
 
     return clustering.network, clustering.busmap
 
diff --git a/scripts/solve_network.py b/scripts/solve_network.py
index db64e576..24cd0464 100755
--- a/scripts/solve_network.py
+++ b/scripts/solve_network.py
@@ -241,7 +241,7 @@ def extra_functionality(n, snapshots):
     add_battery_constraints(n)
 
 
-def solve_network(n, config, solver_log=None, opts='', **kwargs):
+def solve_network(n, config, opts='', **kwargs):
     solver_options = config['solving']['solver'].copy()
     solver_name = solver_options.pop('name')
     cf_solving = config['solving']['options']
@@ -282,8 +282,9 @@ if __name__ == "__main__":
     with memory_logger(filename=fn, interval=30.) as mem:
         n = pypsa.Network(snakemake.input[0])
         n = prepare_network(n, solve_opts)
-        n = solve_network(n, config=snakemake.config, solver_dir=tmpdir,
-                          solver_log=snakemake.log.solver, opts=opts)
+        n = solve_network(n, config=snakemake.config, opts=opts,
+                          solver_dir=tmpdir,
+                          solver_logfile=snakemake.log.solver)
         n.export_to_netcdf(snakemake.output[0])
 
     logger.info("Maximum memory usage: {}".format(mem.mem_usage))
diff --git a/scripts/solve_operations_network.py b/scripts/solve_operations_network.py
index c65e6889..b698c2f1 100644
--- a/scripts/solve_operations_network.py
+++ b/scripts/solve_operations_network.py
@@ -71,7 +71,7 @@ def set_parameters_from_optimized(n, n_optim):
             n_optim.lines[attr].reindex(lines_untyped_i, fill_value=0.)
     n.lines['s_nom_extendable'] = False
 
-    links_dc_i = n.links.index[n.links.carrier == 'DC']
+    links_dc_i = n.links.index[n.links.p_nom_extendable]
     n.links.loc[links_dc_i, 'p_nom'] = \
         n_optim.links['p_nom_opt'].reindex(links_dc_i, fill_value=0.)
     n.links.loc[links_dc_i, 'p_nom_extendable'] = False
@@ -111,8 +111,9 @@ if __name__ == "__main__":
     fn = getattr(snakemake.log, 'memory', None)
     with memory_logger(filename=fn, interval=30.) as mem:
         n = prepare_network(n, solve_opts=snakemake.config['solving']['options'])
-        n = solve_network(n, config, solver_dir=tmpdir,
-                          solver_log=snakemake.log.solver, opts=opts)
+        n = solve_network(n, config=config, opts=opts,
+                          solver_dir=tmpdir,
+                          solver_logfile=snakemake.log.solver)
         n.export_to_netcdf(snakemake.output[0])
 
     logger.info("Maximum memory usage: {}".format(mem.mem_usage))
diff --git a/test/config.test1.yaml b/test/config.test1.yaml
index a5dadc65..83ce38ad 100755
--- a/test/config.test1.yaml
+++ b/test/config.test1.yaml
@@ -24,7 +24,7 @@ clustering:
 
 snapshots:
   start: "2013-03-01"
-  end: "2014-04-01"
+  end: "2013-03-08"
   closed: 'left' # end is not inclusive
 
 enable:
@@ -61,7 +61,7 @@ atlite:
       module: era5
       x: [4., 15.]
       y: [46., 56.]
-      time: ["2013-03", "2013-03"]
+      time: ["2013-03-01", "2013-03-08"]
 
 renewable:
   onwind: