diff --git a/src/optimizer/optimizer.py b/src/optimizer/optimizer.py
index b878ec8e6..9626701e2 100644
--- a/src/optimizer/optimizer.py
+++ b/src/optimizer/optimizer.py
@@ -54,7 +54,7 @@ class Optimizer:
     """
 
     def __init__(self, strategy: OptimizationStrategy, grid: GridConfig, batteries: List[BatteryConfig], time_series: TimeSeriesData,
-                 eta_c: float = 0.95, eta_d: float = 0.95, M: float = 1e6, optimizer_settings: OptimizerSettings | None = None):
+                 eta_c: float = 0.89, eta_d: float = 0.95, M: float = 1e6, optimizer_settings: OptimizerSettings | None = None):
         """
         Optimizer Constructor
         """
@@ -615,8 +615,10 @@ def get_clean_objective_value(self):
 
         # charge for import power demand rate. The demand rate is applied to the maximum
         # power draw beyond the threshold within the time horizon.
+        p_max_imp_exc = None
         if self.is_grid_demand_rate_active:
-            clean_objective += - self.grid.prc_p_exc_imp \
-                * pulp.value(self.variables['p_max_imp_exc'])
+            p_max_imp_exc = pulp.value(self.variables['p_max_imp_exc'])
+        if p_max_imp_exc is not None:
+            clean_objective += - self.grid.prc_p_exc_imp * p_max_imp_exc
 
         return clean_objective
diff --git a/test_cases/000-default-openapi-example.json b/test_cases/000-default-openapi-example.json
new file mode 100644
index 000000000..8ce561066
--- /dev/null
+++ b/test_cases/000-default-openapi-example.json
@@ -0,0 +1,90 @@
+{
+    "expected_response": {
+        "status": "Optimal",
+        "objective_value": 0,
+        "limit_violations": {
+            "grid_import_limit_exceeded": false,
+            "grid_export_limit_hit": false
+        },
+        "batteries": [
+            {
+            "charging_power": [
+                0
+            ],
+            "discharging_power": [
+                0
+            ],
+            "state_of_charge": [
+                0
+            ]
+            }
+        ],
+        "grid_import": [
+            0
+        ],
+        "grid_export": [
+            0
+        ],
+        "flow_direction": [
+            0
+        ],
+        "grid_import_overshoot": [
+            0
+        ],
+        "grid_export_overshoot": [
+            0
+        ]
+    },
+    "request": {
+        "strategy": {
+            "charging_strategy": "string",
+            "discharging_strategy": "string"
+        },
+        "grid": {
+            "p_max_imp": 0,
+            "p_max_exp": 0,
+            "prc_p_exc_imp": 0
+        },
+        "batteries": [
+            {
+            "charge_from_grid": true,
+            "discharge_to_grid": true,
+            "s_capacity": 0,
+            "s_min": 0,
+            "s_max": 0,
+            "s_initial": 0,
+            "p_demand": [
+                0
+            ],
+            "s_goal": [
+                0
+            ],
+            "c_min": 0,
+            "c_max": 0,
+            "d_max": 0,
+            "p_a": 0,
+            "c_priority": 0
+            }
+        ],
+        "time_series": {
+            "dt": [
+            0
+            ],
+            "gt": [
+            0
+            ],
+            "ft": [
+            0
+            ],
+            "p_N": [
+            0
+            ],
+            "p_E": [
+            0
+            ]
+        },
+        "eta_c": 0.95,
+        "eta_d": 0.95
+    },
+    "test_items": {}
+}
\ No newline at end of file