build_powerplants FuelType and Technology bug

[pz-max]

Describe the Bug

Spotted by @energyLS in PyPSA-Earth, fixed by @Tomkourou, and reviewed by me. It was found out that the FuelType and Technology were not correctly assigned in PyPSA-Earth, leading to the following issue:

PyPSA-Eur trouble code is here:

pypsa-eur/scripts/build_powerplants.py

Lines 100 to 107 in 80eadcf

	def replace_natural_gas_technology(df):
	mapping = {"Steam Turbine": "OCGT", "Combustion Engine": "OCGT"}
	tech = df.Technology.replace(mapping).fillna("OCGT")
	return df.Technology.where(df.Fueltype != "Natural Gas", tech)
	def replace_natural_gas_fueltype(df):
	return df.Fueltype.where(df.Fueltype != "Natural Gas", df.Technology)

Recommended changes in the PyPSA-Earth PR applicable to PyPSA-Eur:

• assume that steam turbine is actually CCGT (steam turbine + gas turbine)
• fix assignment bug in replace_natural_gas_fueltype()
• replace .where by .mask for readability improvement

The changes lead to the following correct results:

[pz-max]

Let us know if you think the bug should also be fixed in PyPSA-Eur. I am sure we can create a PR on this :)