test: solar PV arrays must round-trip through persistence 🟥

sap_energy_source.photovoltaic_arrays has no table, so every array is
dropped on save — worth ~12 SAP points on an electrically-heated dwelling
(persist != score). Inject two ordered arrays onto a PV-free fixture.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/repositories/epc/test_epc_round_trip.py

@@ -86,6 +86,44 @@ def test_non_separated_conservatory_round_trips(db_engine: Engine) -> None:
     assert reloaded == original
 
 
+def test_photovoltaic_arrays_round_trip(db_engine: Engine) -> None:
+    # SAP 10.2 Appendix M — a dwelling's solar PV arrays generate electricity that
+    # offsets demand, worth a large slice of the SAP score (≈12 points on an
+    # electrically-heated dwelling). `sap_energy_source.photovoltaic_arrays` had
+    # no table, so every array was dropped on save (persist != score). We inject
+    # two arrays (distinct, so ORDER is observable) onto a clean PV-free fixture
+    # so the ONLY thing that can break deep-equality is the array list itself.
+    from dataclasses import replace
+
+    from datatypes.epc.domain.epc_property_data import PhotovoltaicArray
+
+    # Arrange — a green fixture with no PV, plus two ordered arrays.
+    original = _load_epc("RdSAP-Schema-21.0.1")
+    assert original.sap_energy_source.photovoltaic_arrays is None, (
+        "fixture must start PV-free so the array list is the only variable"
+    )
+    arrays = [
+        PhotovoltaicArray(peak_power=3.24, pitch=3, overshading=1, orientation=3),
+        PhotovoltaicArray(peak_power=1.5, pitch=2, overshading=2, orientation=None),
+    ]
+    original = replace(
+        original,
+        sap_energy_source=replace(
+            original.sap_energy_source, photovoltaic_arrays=arrays
+        ),
+    )
+
+    # Act
+    with Session(db_engine) as session:
+        epc_property_id = EpcPostgresRepository(session).save(original)
+        session.commit()
+    with Session(db_engine) as session:
+        reloaded = EpcPostgresRepository(session).get(epc_property_id)
+
+    # Assert — both arrays survive in order, deep-equal.
+    assert reloaded == original
+
+
 def test_floor_dimension_heat_loss_flags_round_trip(db_engine: Engine) -> None:
     # SAP 10.2 §3.3 — `is_exposed_floor` and `is_above_partially_heated_space`
     # are heat-loss flags on a `SapFloorDimension`: the calculator routes a floor