Regression in #519a4f2: Adding `p_max_pu` for `conventional_carriers` through `.csv` file

[euronion]

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

(currently migrating from version 0.8.0 to current master)

With commit #591a4f2 and specifically here

pypsa-eur/rules/build_electricity.smk

Lines 331 to 342 in d7554bc

	input:
	**{
	f"profile_{tech}": RESOURCES + f"profile_{tech}.nc"
	for tech in config["electricity"]["renewable_carriers"]
	},
	**{
	f"conventional_{carrier}_{attr}": fn
	for carrier, d in config.get("conventional", {None: {}}).items()
	if carrier in config["electricity"]["conventional_carriers"]
	for attr, fn in d.items()
	if str(fn).startswith("data/")
	},

providing a filename to a data/*.csv file in the config like

pypsa-eur/config/config.default.yaml

Lines 228 to 229 in d7554bc

	nuclear:
	p_max_pu: "data/nuclear_p_max_pu.csv" # float of file name

only works if the conventional_carrier is also specified here:

pypsa-eur/config/config.default.yaml

Line 113 in d7554bc

conventional_carriers: [nuclear, oil, OCGT, CCGT, coal, lignite, geothermal, biomass]

but that also causes existing powerplants to be included.

Before it was possible to not have existing powerplants included but allow for e.g. conventional power plants via

pypsa-eur/config/config.default.yaml

Line 105 in d7554bc

Generator: [solar, onwind, offwind-ac, offwind-dc, OCGT]

to have those types extendable and put in p_max_pu via the config line above linking to data/*.csv files.

Not sure if that was intentionally changed, but it seems like it is now no longer possible to have p_max_pu through .csv file + no existing powerplant capacities + extendable powerplant capacities via config.

Error Message

(weird failures, because the filename is added as p_max_pu instead of the values.

[fneum]

I had a similar issue where it was not possible to add wind and solar without existing capacity anymore.