Negative electrical demand with coarse time resolution

[cerealice]

Checklist

• I am using the current master branch.
• I am running on an up-to-date pypsa-eur environment. Update via conda env update -f envs/environment.yaml.

Describe the Bug

When I use a very aggregated time resolution (876H) my electricity demand becomes negative because in prepare_sector_network in add_industry the factor to remove the industrial electricity demand does not take into account the fact that the load is not on an hourly basis.
I solved this by creating inside add_industry a timesteo variable timestep = n.snapshot_weightings.iloc[0,0] and then using it to weight better the loads_t.p

[koen-vg]

Could this simply be caused by setting resolution_elec to some non-false value but running a sector-coupled network? Currently, prepare_sector_network.py basically expects resolution_elec to be False, i.e. the network is not "supposed" to be time-aggreggated, and for sector-coupled networks this is only supposed to happen through resolution_sector. See also the discussion in #1277. I will note that this is warned against in the documentation (https://pypsa-eur.readthedocs.io/en/latest/configuration.html#clustering), but that's of course easy to miss, and as I've written in the linked issue I don't think there should be any reason to allow two separate configuration option for elec-only and sector-coupled time resolution; by joining them we could avoid the kind of issues like the present one.

Hopefully the problem with negative demand goes away when you set resolution_elec: false. If it does, I would close this issue and we can keep discussing potential improvements to how time-aggregation in implemented in #1277.

[cerealice]

I confirm that the problem is solved when running a sector coupled network but with resolution_elec: false. It is indeed specified in the documentation
Still it would be interesting to continue on #1277.
Thanks for your help!