Offshore Wind Potential Correction

Checklist

• [X ] I am using the current master branch or the latest release. Please indicate.
• [ X] I am running on an up-to-date pypsa-eur environment. Update via conda env update -f envs/environment.yaml.

Describe the Bug

The current offshore wind potential with the settings given in config.default.yaml leads to a total offshore potential of 32 GW in Germany. The political target atm is 70 GW in 2045. In order to allow the model to expand further either a country specific capacity_per_sqkm: needs to be implemented.
The capapacity_per_sqkm is expected to be between 6-8 for Germany

Error Message

Generator-ext-p_nom-upper[DE1 3 offwind-ac-2035]: +1 Generator-p_nom[DE1 3 offwind-ac-2035] ≤ 1476.41315085
Generator-ext-p_nom-upper[DE1 3 offwind-dc-2035]: +1 Generator-p_nom[DE1 3 offwind-dc-2035] ≤ 19429.4347882
Generator-ext-p_nom-upper[DE1 6 offwind-ac-2035]: +1 Generator-p_nom[DE1 6 offwind-ac-2035] ≤ 2492.76843506
Generator-ext-p_nom-upper[DE1 6 offwind-dc-2035]: +1 Generator-p_nom[DE1 6 offwind-dc-2035] ≤ 1449.20824617
Generator-ext-p_nom-upper[DE1 7 offwind-ac-2035]: +1 Generator-p_nom[DE1 7 offwind-ac-2035] ≤ 1104.12646493
Generator-ext-p_nom-upper[DE1 7 offwind-dc-2035]: +1 Generator-p_nom[DE1 7 offwind-dc-2035] ≤ 257.203999356
GlobalConstraint-capacity_minimum-DE-Generator-offwind: +1 Generator-p_nom[DE1 3 offwind-ac-2035] + 1 Generator-p_nom[DE1 3 offwind-dc-2035] + 1 Generator-p_nom[DE1 6 offwind-ac-2035] + 1 Generator-p_nom[DE1 6 offwind-dc-2035] + 1 Generator-p_nom[DE1 7 offwind-ac-2035] + 1 Generator-p_nom[DE1 7 offwind-dc-2035] ≥ 31871
ERROR:root:Uncaught exception

Start with config.default.yaml and the offshore wind potential calculation that produces the Generator-ext_p_nom-upper limits shown in the error. Check envs/environment.yaml to reproduce the issue, then trace how capacity_per_sqkm is applied by country; done means Germany can represent the requested higher offshore wind potential without violating the resulting constraints.