fix: prevent multi counting of capacity

src/oge/helpers.py

@@ -394,21 +394,33 @@ def add_plant_nameplate_capacity(df: pd.DataFrame) -> pd.DataFrame:
     Returns:
         pd.DataFrame: original data frame with additional 'capacity_mw' column.
     """
-    generators_capacity = load_data.load_pudl_table(
+    generator_capacity = load_data.load_pudl_table(
         "generators_eia860",
+        year=earliest_data_year,
+        end_year=latest_validated_year,
         columns=["plant_id_eia", "generator_id", "report_date", "capacity_mw"],
+    ).sort_values(by=["plant_id_eia", "generator_id", "report_date"], ascending=True)
+
+    generator_capacity["capacity_mw"] = generator_capacity.groupby(
+        ["plant_id_eia", "generator_id"]
+    )["capacity_mw"].bfill()
+    generator_capacity["capacity_mw"] = generator_capacity.groupby(
+        ["plant_id_eia", "generator_id"]
+    )["capacity_mw"].ffill()
+
+    # keep only the most recent year of data
+    generator_capacity = generator_capacity.drop_duplicates(
+        subset=["plant_id_eia", "generator_id"], keep="last"
     )
-    generators_capacity[
-        generators_capacity["report_date"] == generators_capacity["report_date"].max()
-    ]
-    plants_capacity = (
-        generators_capacity.groupby(["plant_id_eia"])["capacity_mw"]
+
+    plant_capacity = (
+        generator_capacity.groupby(["plant_id_eia"])["capacity_mw"]
         .sum()
         .round(2)
         .reset_index()
     )
 
-    df = df.merge(plants_capacity, how="left", on=["plant_id_eia"], validate="1:1")
+    df = df.merge(plant_capacity, how="left", on=["plant_id_eia"], validate="1:1")
 
     return df