diff --git a/.travis.yml b/.travis.yml
index 011753f4..0fe59eb1 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -20,7 +20,7 @@ before_install:
   - conda activate pypsa-eur
 
   # install open-source solver
-  - mamba install -c conda-forge ipopt glpk
+  - mamba install -c conda-forge glpk ipopt
 
   # list packages for easier debugging
   - conda list
diff --git a/doc/release_notes.rst b/doc/release_notes.rst
index 1cae0807..f2192490 100644
--- a/doc/release_notes.rst
+++ b/doc/release_notes.rst
@@ -25,6 +25,10 @@ Upcoming Release
 
 * Don't remove capital costs from lines and links, when imposing a line volume limit (wildcard ``lv``) or a line cost limit (``lc``). Previously, these were removed to move the expansion in direction of the limit.
 
+* Fix bug of clustering offwind-{ac,dc} sites in the option of high-resolution sites for renewables. Now, there are more sites for offwind-{ac,dc} available than network nodes. Before, they were clustered to the resolution of the network. (e.g. elec_s1024_37m.nc: 37 network nodes, 1024 sites)
+
+* Use `mamba` (https://github.com/mamba-org/mamba) for faster Travis CI builds (`#196 <https://github.com/PyPSA/pypsa-eur/pull/196>`_)
+
 PyPSA-Eur 0.2.0 (8th June 2020)
 ==================================
 
diff --git a/envs/environment.yaml b/envs/environment.yaml
index fb4019a3..f970e894 100644
--- a/envs/environment.yaml
+++ b/envs/environment.yaml
@@ -12,6 +12,7 @@ dependencies:
   - python
   - pip
   - pre-commit
+  - mamba # esp for windows build
 
   - pypsa>=0.17.1
   - atlite=0.0.3
@@ -21,7 +22,7 @@ dependencies:
   - scikit-learn
   - pycountry
   - seaborn
-  - snakemake-minimal
+  - snakemake-minimal<=5.24.2 # until https://github.com/snakemake/snakemake/issues/635 closed
   - memory_profiler
   - yaml
   - pytables
@@ -48,7 +49,7 @@ dependencies:
   - geopandas
   - rasterio
   - shapely
-  - libgdal
+  - libgdal<=3.0.2
 
   # Solvers
   - gurobi:gurobi # until https://github.com/conda-forge/pypsa-feedstock/issues/4 closed
diff --git a/scripts/cluster_network.py b/scripts/cluster_network.py
index fc054a10..4ecd2e05 100644
--- a/scripts/cluster_network.py
+++ b/scripts/cluster_network.py
@@ -251,8 +251,8 @@ def busmap_for_n_clusters(n, n_clusters, solver_name, focus_weights=None, algori
         else:
             raise ValueError(f"`algorithm` must be one of 'kmeans', 'spectral' or 'louvain'. Is {algorithm}.")
 
-    return (n.buses.groupby(['country', 'sub_network'], group_keys=False, squeeze=True)
-            .apply(busmap_for_country).rename('busmap'))
+    return (n.buses.groupby(['country', 'sub_network'], group_keys=False)
+            .apply(busmap_for_country).squeeze().rename('busmap'))
 
 
 def clustering_for_n_clusters(n, n_clusters, aggregate_carriers=None,
@@ -333,7 +333,7 @@ if __name__ == "__main__":
 
     renewable_carriers = pd.Index([tech
                                    for tech in n.generators.carrier.unique()
-                                   if tech.split('-', 2)[0] in snakemake.config['renewable']])
+                                   if tech in snakemake.config['renewable']])
 
     if snakemake.wildcards.clusters.endswith('m'):
         n_clusters = int(snakemake.wildcards.clusters[:-1])
diff --git a/scripts/prepare_network.py b/scripts/prepare_network.py
index f790db8f..ac81955d 100755
--- a/scripts/prepare_network.py
+++ b/scripts/prepare_network.py
@@ -185,7 +185,8 @@ if __name__ == "__main__":
 
     for o in opts:
         oo = o.split("+")
-        if oo[0].startswith(tuple(n.carriers.index)):
+        suptechs = map(lambda c: c.split("-", 2)[0], n.carriers.index)
+        if oo[0].startswith(tuple(suptechs)):
             carrier = oo[0]
             cost_factor = float(oo[1])
             if carrier == "AC":  # lines do not have carrier