Electricity-Only example fails to complete clustering with HiGHs and SCIP ("Solver scip does not support quadratic problems").

[ZilentKnight]

Version Checks (indicate both or one)

• I have confirmed this bug exists on the lastest release of PyPSA-Eur.

• I have confirmed this bug exists on the current master branch of PyPSA-Eur.

Issue Description

Hi!

I am trying to run the tutorial electricity-only but I keep getting an error when it reaches clustering and tries to solve the problem using open-source solvers (HiGHs, SCIP, CoinCBC).
ValueError: Solver scip does not support quadratic problems.

I have not modified config.electricity.yaml and I could not find anyone else raising the same error.
It work when I tried to use Gurobi's solver (without a license), but this is not an option for my future application.

Thank you in advance.

Log

Clustering network to 6 clusters
localrule cluster_network:
    input: resources/test-elec/networks/base_s.nc, resources/test-elec/admin_shapes.geojson, resources/test-elec/regions_onshore_base_s.geojson, resources/test-elec/regions_offshore_base_s.geojson, resources/test-elec/electricity_demand_base_s.nc
    output: resources/test-elec/networks/base_s_6.nc, resources/test-elec/regions_onshore_base_s_6.geojson, resources/test-elec/regions_offshore_base_s_6.geojson, resources/test-elec/busmap_base_s_6.csv, resources/test-elec/linemap_base_s_6.csv
    log: logs/test-elec/cluster_network_base_s_6.log
    jobid: 18
    benchmark: benchmarks/test-elec/cluster_network_base_s_6
    reason: Missing output files: resources/test-elec/networks/base_s_6.nc, resources/test-elec/busmap_base_s_6.csv, resources/test-elec/regions_onshore_base_s_6.geojson, resources/test-elec/regions_offshore_base_s_6.geojson
    wildcards: clusters=6
    resources: tmpdir=C:\Users\user\AppData\Local\Temp, mem_mb=10000, mem=10 GB, mem_mib=9537
WARNING: All log messages before absl::InitializeLog() is called are written to STDERR
E0000 00:00:1771924503.963646   43676 instrument.cc:563] Metric with name 'grpc.resource_quota.calls_dropped' registered more than once. Ignoring later registration.
E0000 00:00:1771924503.963812   43676 instrument.cc:563] Metric with name 'grpc.resource_quota.calls_rejected' registered more than once. Ignoring later registration.
E0000 00:00:1771924503.963852   43676 instrument.cc:563] Metric with name 'grpc.resource_quota.connections_dropped' registered more than once. Ignoring later registration.
E0000 00:00:1771924503.963880   43676 instrument.cc:563] Metric with name 'grpc.resource_quota.instantaneous_memory_pressure' registered more than once. Ignoring later registration.
E0000 00:00:1771924503.963914   43676 instrument.cc:563] Metric with name 'grpc.resource_quota.memory_pressure_control_value' registered more than once. Ignoring later registration.
WARNING:pypsa.network.io:Importing network from PyPSA version v1.0.7 while current version is v1.1.2. Read the release notes at `https://go.pypsa.org/release-notes` to prepare your network for import.
INFO:pypsa.network.io:Imported network 'PyPSA-Eur (osm vlatest)' has buses, carriers, lines, shapes
INFO:__main__:The configured solver `highs` does not support quadratic objectives. Falling back to `scip`.
INFO:linopy.model: Solve problem using Scip solver
ERROR:root:Uncaught exception
Traceback (most recent call last):
  File "C:\Users\user\github\pypsa-eur_test\.snakemake\scripts\tmp8p52w33p.cluster_network.py", line 676, in <module>
    n_clusters_c = distribute_n_clusters_to_countries(
        n,
    ...<3 lines>...
        solver_name=solver_name,
    )
  File "C:\Users\user\github\pypsa-eur_test\.snakemake\scripts\tmp8p52w33p.cluster_network.py", line 346, in distribute_n_clusters_to_countries
    m.solve(solver_name=solver_name)
    ~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\user\github\pypsa-eur_test\.pixi\envs\default\Lib\site-packages\linopy\model.py", line 1352, in solve
    raise ValueError(
        f"Solver {solver_name} does not support quadratic problems."
    )

Reproducible Example

pixi shell
snakemake -call results/test-elec/networks/base_s_6_elec_.nc --configfile config/test/config.electricity.yaml

Expected Behavior

Clustering cannot be solved because "Solver SCIP does not support quadratic problems".

Traceback (most recent call last):
  File "C:\Users\user\github\pypsa-eur_test\.snakemake\scripts\tmp8p52w33p.cluster_network.py", line 676, in <module>
    n_clusters_c = distribute_n_clusters_to_countries(
        n,
    ...<3 lines>...
        solver_name=solver_name,
    )
  File "C:\Users\user\github\pypsa-eur_test\.snakemake\scripts\tmp8p52w33p.cluster_network.py", line 346, in distribute_n_clusters_to_countries
    m.solve(solver_name=solver_name)
    ~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\user\github\pypsa-eur_test\.pixi\envs\default\Lib\site-packages\linopy\model.py", line 1352, in solve
    raise ValueError(
        f"Solver {solver_name} does not support quadratic problems."
    )

Installed Versions

I have attached the pixi.lock-file, as its content was too large.
pixi.lock.txt

[ZilentKnight]

This is not directly caused by PyPSA-Eur but by a change to linopy December 2025 PyPSA/linopy@a1a2814 where SCIP's quadratic support is disabled for Windows systems.

Manually overwriting solver capabilities (see PyPSA/linopy#588) resolves this issue.