From c40c46aeda2a5887f6bc7bdc40f34513a24ea8e0 Mon Sep 17 00:00:00 2001
From: Javier Lopez Lorente <Javier.Lorente@dnv.com>
Date: Fri, 8 May 2026 16:21:32 +0200
Subject: [PATCH] Add support for availability losses in PVSystem class

---
 solarfarmer/models/pvsystem/pvsystem.py | 10 +++++++
 tests/test_pvsystem.py                  | 37 +++++++++++++++++++++++++
 2 files changed, 47 insertions(+)

diff --git a/solarfarmer/models/pvsystem/pvsystem.py b/solarfarmer/models/pvsystem/pvsystem.py
index 4f4eb69..458a16f 100644
--- a/solarfarmer/models/pvsystem/pvsystem.py
+++ b/solarfarmer/models/pvsystem/pvsystem.py
@@ -126,6 +126,10 @@ class PVSystem:
         `dc_ohmic_loss` and `ac_ohmic_loss`.
     transformer_stages: int
         Number of transformer stages. 0 for ideal behaviour or 1 for one stage (default is 1).
+    plant_unavailability : float
+        Plant availability loss (per unit) (default 0.0, i.e., no unavailability loss).
+    grid_unavailability : float
+        Grid availability loss (per unit) (default 0.0, i.e., no unavailability loss).
 
     Auxiliary Files
     ---------------
@@ -252,6 +256,8 @@ class PVSystem:
     bifacial: bool = False
     inverter_type: InverterType | None = InverterType.CENTRAL
     transformer_stages: int = 1
+    plant_unavailability: float = 0.0
+    grid_unavailability: float = 0.0
 
     # Effects and settings
     mounting_height: float | None = None  # Changed from: mounting_height: float
@@ -804,6 +810,8 @@ def describe(self, verbose=False) -> None:
         print(
             f"Transformer Stages: {self.transformer_stages} (0=Ideal/NoLoss, 1=MV/HV transformer)"
         )
+        print(f"Plant Unavailability: {self.plant_unavailability} (per unit)")
+        print(f"Grid Unavailability: {self.grid_unavailability} (per unit)")
 
         if verbose:
             # Losses
@@ -1117,6 +1125,8 @@ def construct_plant(pvplant: PVSystem) -> str:
     )
     calculation_options.apply_spectral_mismatch_modifier = pvplant.enable_spectral_modeling
     calculation_options.calculate_dhi = pvplant.calculate_dhi_from_ghi
+    calculation_options.system_availability_loss = pvplant.plant_unavailability
+    calculation_options.grid_availability_loss = pvplant.grid_unavailability
 
     # Build the full inputs model
     inputs = EnergyCalculationInputs(
diff --git a/tests/test_pvsystem.py b/tests/test_pvsystem.py
index fc1ecce..c8c8060 100644
--- a/tests/test_pvsystem.py
+++ b/tests/test_pvsystem.py
@@ -515,6 +515,43 @@ def test_aux_loss_present_in_payload(self, bern_2d_racks_inputs):
         assert payload["pvPlant"]["auxiliaryLosses"]["simpleLossFactor"] == 0.01
 
 
+class TestPVSystemUnavailability:
+    """Tests for plant_unavailability and grid_unavailability properties."""
+
+    def test_unavailability_defaults_are_zero(self):
+        """plant_unavailability and grid_unavailability must default to 0.0."""
+        plant = PVSystem()
+
+        assert plant.plant_unavailability == 0.0
+        assert plant.grid_unavailability == 0.0
+
+    def test_unavailability_custom_values_are_stored(self):
+        """Custom unavailability values must be stored on the instance."""
+        plant = PVSystem(plant_unavailability=0.03, grid_unavailability=0.01)
+
+        assert plant.plant_unavailability == 0.03
+        assert plant.grid_unavailability == 0.01
+
+    def test_unavailability_propagates_to_payload(self, bern_2d_racks_inputs):
+        """Non-zero unavailability values must appear in energyCalculationOptions in the payload."""
+        plant = PVSystem(
+            latitude=46.9,
+            longitude=7.4,
+            plant_unavailability=0.03,
+            grid_unavailability=0.01,
+        )
+        plant.pan_files = {
+            "CanadianSolar_CS6U-330M_APP": f"{bern_2d_racks_inputs}/CanadianSolar_CS6U-330M_APP.PAN"
+        }
+        plant.ond_files = {"Sungrow_SG125HV_APP": f"{bern_2d_racks_inputs}/Sungrow_SG125HV_APP.OND"}
+
+        payload = json.loads(construct_plant(plant))
+        opts = payload["energyCalculationOptions"]
+
+        assert opts["systemAvailabilityLoss"] == 0.03
+        assert opts["gridAvailabilityLoss"] == 0.01
+
+
 class TestPVSystemBifacial:
     """Tests for bifacial parameter initialization (Phase 1 bug fix)."""