Use the VOM/FOM cost data at the build year of the existing power plants

Feature Request

Currently in add_electricity.py and add_extracomponents.py, we assign the VOM/FOM cost data of the planning year (say 2050) to the existing power plants. It would be better to change it to the build year (say 2010)? There could be a ~30% difference for gas power plants.

    attach_conventional_generators(
        n,
        costs,
        plants,
        conventional_carriers,
        extendable_carriers,
        params.conventional,
        renewable_carriers,
        conventional_inputs,
        unit_commitment=params.conventional["unit_commitment"],
        fuel_price=None,  # update fuel prices later
    )

    if snakemake.params.retirement == "economic":
        economic_retirement_gens = set(elec_config.get("conventional_carriers", None))
        split_retirement_gens(
            n,
            costs_dict[n.investment_periods[0]],
            economic_retirement_gens,
            economic=True,
        )

Suggested Solution

No response

Additional Info

No response

Start with add_electricity.py and add_extracomponents.py, then trace attach_conventional_generators and the economic-retirement split_retirement_gens call. Determine how existing plants' build years are represented and update the cost lookup so VOM/FOM uses those years rather than the planning year; done when both paths consistently apply build-year costs.