Length_factor multiplied twice

[lindnemi]

I just had a thorough look with @p-glaum at the length_factor. As far as we understand, in the clustered network, the length of all lines is set to the haversine distance between the buses multiplied by length_factor.

https://github.com/PyPSA/PyPSA/blob/068ca0b3397194390493ccc140ad0c79a2ea7310/pypsa/clustering/spatial.py#L397-L400

However, the capital costs in add_electricity consider the length factor a second time:

pypsa-eur/scripts/add_electricity.py

Lines 433 to 437 in 35050d9

	n.lines["capital_cost"] = (
	n.lines["length"]
	* line_length_factor
	* costs.at["HVAC overhead", "capital_cost"]
	)

Thus we might be overestimating the capital_cost of lines, with the default setting by 25%. The same probably also applies to links.