fix(battery): preserve energy below minimum state of charge (#1483)

src/akkudoktoreos/devices/genetic/battery.py

@@ -366,6 +366,9 @@ class Battery:
 
         # Raw extractable energy above minimum SoC
         raw_available_wh = max(self.soc_wh - self.min_soc_wh, 0.0)
+        if raw_available_wh == 0.0:
+            # A measured SoC below the reserve must not be raised by discharging.
+            return 0.0, 0.0
 
         # Maximum raw discharge due to power limit, scaled to the slot duration.
         # max_charge_power_w is a power [W]; energy movable in one slot is

src/akkudoktoreos/devices/genetic/inverter.py

@@ -304,6 +304,9 @@ class Inverter:
         discharged_raw_wh = battery._discharged_raw_wh_per_slot
         discharging_efficiency = battery.discharging_efficiency
         raw_available_wh = max(soc_wh - min_soc_wh, 0.0)
+        if raw_available_wh == 0.0:
+            # Match Battery.discharge_energy(): preserve a SoC below the reserve.
+            return 0.0, 0.0
         max_raw_wh = max(
             battery.max_charge_power_w * battery.slot_duration_h - discharged_raw_wh[hour], 0.0
         )

src/akkudoktoreos/devices/genetic0/genetic0battery.py

@@ -227,6 +227,9 @@ class Genetic0Battery:
 
         # Raw extractable energy above minimum SoC
         raw_available_wh = max(self.soc_wh - self.min_soc_wh, 0.0)
+        if raw_available_wh == 0.0:
+            # A measured SoC below the reserve must not be raised by discharging.
+            return 0.0, 0.0
 
         # Maximum raw discharge due to power limit
         max_raw_wh = self.max_charge_power_w  # TODO rename to max_discharge_power_w

tests/test_genetic0battery.py

@@ -119,6 +119,20 @@ def test_battery_discharge_exactly_min_soc(setup_pv_battery):
     assert battery.current_soc_percentage() == 20  # SOC should remain at min_SOC
 
 
+@pytest.mark.parametrize("initial_soc", [0, 5, 20])
+@pytest.mark.parametrize("requested_wh", [0.0, 280.0])
+def test_discharge_preserves_energy_at_or_below_min_soc(
+    setup_pv_battery, initial_soc, requested_wh
+):
+    battery = setup_pv_battery
+    battery.soc_wh = initial_soc / 100 * battery.capacity_wh
+    initial_wh = battery.soc_wh
+
+    for slot in (0, 0, 1):
+        assert battery.discharge_energy(requested_wh, slot) == (0.0, 0.0)
+        assert battery.soc_wh == initial_wh
+
+
 def test_battery_charge_exactly_max_soc(setup_pv_battery):
     battery = setup_pv_battery
     battery.soc_wh = battery.max_soc_wh  # Set battery to exactly max SOC

tests/test_geneticbattery.py

@@ -114,6 +114,31 @@ def test_battery_discharge_when_empty(setup_pv_battery):
     assert battery.current_soc_percentage() == 20, "SoC should remain at min_soc"
 
 
+@pytest.mark.parametrize("slot_duration_h", [0.25, 1.0])
+@pytest.mark.parametrize("initial_soc", [0, 5, 6])
+@pytest.mark.parametrize("requested_wh", [0.0, 280.0])
+def test_discharge_preserves_energy_at_or_below_min_soc(
+    slot_duration_h, initial_soc, requested_wh
+):
+    battery = Battery(
+        SolarPanelBatteryParameters(
+            device_id="battery1",
+            capacity_wh=26_400,
+            initial_soc_percentage=initial_soc,
+            min_soc_percentage=6,
+        ),
+        prediction_hours=2,
+        slot_duration_h=slot_duration_h,
+    )
+    battery.set_discharge_per_hour(np.ones(2))
+    initial_wh = battery.soc_wh
+
+    for slot in (0, 0, 1):
+        assert battery.discharge_energy(requested_wh, slot) == (0.0, 0.0)
+        assert battery.soc_wh == initial_wh
+        assert battery.discharged_energy_wh(slot) == 0.0
+
+
 def test_battery_discharge_exactly_min_soc(setup_pv_battery):
     battery = setup_pv_battery
     battery.soc_wh = battery.min_soc_wh  # Set battery to exactly min SOC

tests/test_geneticsimulation.py

@@ -25,6 +25,65 @@ from akkudoktoreos.utils.datetimeutil import to_duration, to_time
 start_hour = 1
 
 
+@pytest.mark.parametrize("efficiency_curve", [None, [(0.0, 0.8), (1.0, 0.97)]])
+def test_below_min_soc_requires_real_charging_energy(efficiency_curve):
+    """Discharge attempts before and after partial charging must not create energy."""
+    battery = Battery(
+        SolarPanelBatteryParameters(
+            device_id="battery1",
+            capacity_wh=26_400,
+            initial_soc_percentage=0,
+            min_soc_percentage=6,
+            max_charge_power_w=7_000,
+            charging_efficiency=0.95,
+            discharging_efficiency=0.95,
+        ),
+        prediction_hours=4,
+        slot_duration_h=0.25,
+    )
+    inverter = Inverter(
+        InverterParameters(
+            device_id="inverter1",
+            battery_id="battery1",
+            max_power_wh=10_000,
+            max_ac_charge_power_w=6_000,
+            ac_to_dc_efficiency=0.97,
+            dc_to_ac_efficiency=0.97,
+            dc_to_ac_efficiency_curve=efficiency_curve,
+        ),
+        battery=battery,
+        slot_duration_h=0.25,
+    )
+    simulation = GeneticSimulation()
+    simulation.prepare(
+        GeneticEnergyManagementParameters(
+            pv_forecast_wh=[0.0] * 4,
+            total_load=[280.0] * 4,
+            electricity_price_per_wh=[0.00037, 0.00037, 0.00050, 0.00063],
+            feed_in_tariff_per_wh=0.0,
+            price_per_wh_battery=0.0,
+        ),
+        optimization_hours=4,
+        prediction_hours=4,
+        inverter=inverter,
+    )
+    assert simulation.ac_charge_hours is not None
+    assert simulation.bat_discharge_hours is not None
+    simulation.ac_charge_hours[:] = [0.0, 1.0, 0.0, 0.0]
+    simulation.bat_discharge_hours[:] = [1.0, 0.0, 1.0, 1.0]
+
+    result = simulation.simulate(0)
+
+    stored_wh = 1_500 * 0.97 * 0.95
+    assert result["akku_soc_pro_stunde"] == pytest.approx(
+        [0.0, 0.0, stored_wh / 26_400 * 100, stored_wh / 26_400 * 100]
+    )
+    assert result["Netzbezug_Wh_pro_Stunde"] == pytest.approx([280, 1780, 280, 280])
+    assert battery.soc_wh == pytest.approx(stored_wh)
+    assert battery.soc_wh < battery.min_soc_wh
+    assert result["Gesamt_Verluste"] == pytest.approx(1_500 - stored_wh)
+
+
 # Example initialization of necessary components
 @pytest.fixture
 def genetic_simulation(config_eos) -> GeneticSimulation: