Missing Offshore capacity

[toniseibold]

Checklist

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

Describe the Bug

In rule add_existing_baseyear function add_existing_renewables the data from IRENA does not distinguish between Offshore-AC and Offshore-DC but only provides information for Offshore.
However, in add_electricity all renewable generators are added according to config["renewables"]. This leads to the carriers not matching and not adding any existing offshore capacity.

Line 94 and following

gens = n.generators.index[
                (n.generators.index.str[:2] == country)
                & (n.generators.carrier == carrier)
            ]