diff --git a/costs/cost.py b/costs/cost.py
index b25b061..537a23b 100644
--- a/costs/cost.py
+++ b/costs/cost.py
@@ -114,9 +114,7 @@ class Cost:
         global_capital_incomes['Subsidies PV']
     )
 
-    life_cycle_costs_capital_skin = Cost._npv_from_list(
-      self._configuration.discount_rate, df_capital_costs_skin.values.tolist()
-    )
+    life_cycle_costs_capital_skin = self._npv_from_list(df_capital_costs_skin.values.tolist())
     life_cycle_costs_capital_systems = self._npv_from_list(df_capital_costs_systems.values.tolist())
     life_cycle_costs_end_of_life_costs = self._npv_from_list(df_end_of_life_costs.values.tolist())
     life_cycle_operational_costs = self._npv_from_list(df_operational_costs.values.tolist())
diff --git a/costs/total_operational_costs.py b/costs/total_operational_costs.py
index ec44735..b3f97dd 100644
--- a/costs/total_operational_costs.py
+++ b/costs/total_operational_costs.py
@@ -75,12 +75,11 @@ class TotalOperationalCosts(CostBase):
       self._yearly_operational_costs.at[year, 'Fixed_costs_electricity_peak'] = (
           peak_electricity_cost_year_0 * price_increase_peak_electricity
       )
-
       self._yearly_operational_costs.at[year, 'Fixed_costs_electricity_monthly'] = (
           monthly_electricity_cost_year_0 * price_increase_peak_electricity
       )
-      self._yearly_operational_costs.at[year, 'Variable_costs_electricity'] = float(
-        variable_electricity_cost_year_0 * price_increase_electricity
+      self._yearly_operational_costs.at[year, 'Variable_costs_electricity'] = (
+        float(variable_electricity_cost_year_0.iloc[0] * price_increase_electricity)
       )
       self._yearly_operational_costs.at[year, 'Fixed_costs_gas'] = fixed_gas_cost_year_0 * price_increase_gas
       self._yearly_operational_costs.at[year, 'Variable_costs_gas'] = (