test(pv): credit PV only when connected to dwelling meter (pv_connection) 🟥

RdSAP 10 §11.1 / SAP 10.2 Appendix M: PV is included in a dwelling's
assessment only if connected to the dwelling's own electricity meter. The
gov-API pv_connection enum encodes this — 0=no PV, 1=present-but-not-
connected, 2=connected. Corpus-validated (57 PV certs: pv_connection=1 MAE
4.48->1.22 without credit, 0/5 need it; pv_connection=2 needs it, MAE 0.98
vs 10.29) and Elmhurst-proven (connected SAP 87 vs not-connected 74).

cert_to_inputs currently credits a pv_connection=1 array; the test pins that
it must contribute zero generation. Adds pv_connection to make_minimal_sap10_epc.

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

domain/sap10_ml/tests/_fixtures.py

@@ -267,6 +267,7 @@ def make_minimal_sap10_epc(
     sap_heating: Optional[SapHeating] = None,
     photovoltaic_arrays: Optional[list[PhotovoltaicArray]] = None,
     photovoltaic_supply_percent_roof_area: Optional[int] = None,
+    pv_connection: Optional[int] = None,
     mains_gas: bool = True,
     electricity_smart_meter_present: bool = False,
     gas_smart_meter_present: bool = False,
@@ -308,6 +309,7 @@ def make_minimal_sap10_epc(
         sap_energy_source=SapEnergySource(
             mains_gas=mains_gas,
             meter_type="Single",
+            pv_connection=pv_connection,
             pv_battery_count=pv_battery_count,
             wind_turbines_count=wind_turbines_count,
             gas_smart_meter_present=gas_smart_meter_present,

tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py

@@ -40,6 +40,7 @@ from domain.sap10_ml.tests._fixtures import (
     make_floor_dimension,
     make_main_heating_detail,
     make_minimal_sap10_epc,
+    make_pv_array,
     make_sap_heating,
     make_window,
 )
@@ -8387,3 +8388,38 @@ def test_heat_pump_water_scop_not_applied_to_separate_immersion_dhw() -> None:
     # heat pump or a gas boiler (the HP water SCOP does not apply to it).
     assert hp_fuel > 0.0
     assert abs(hp_fuel - boiler_fuel) <= 1e-6
+
+
+def test_pv_credited_only_when_connected_to_dwelling_meter_per_pv_connection() -> None:
+    # RdSAP 10 §11.1 / SAP 10.2 Appendix M: PV-generated electricity is
+    # included in a dwelling's assessment ONLY IF the array is connected to
+    # the dwelling's own electricity meter; an unconnected (communal /
+    # separately-metered) array contributes nothing to the dwelling's energy
+    # cost, CO2 or primary energy. The gov-API `sap_energy_source.pv_connection`
+    # enum encodes this: 0 = no PV, 1 = present but NOT connected, 2 = connected.
+    #
+    # Validated on the RdSAP-21.0.1 corpus (57 PV certs): every pv_connection=1
+    # cert reconciles BETTER without the credit (MAE 4.48 -> 1.22, 0/5 need it),
+    # while pv_connection=2 certs need it (MAE 0.98 vs 10.29 without). Accredited
+    # Elmhurst proof: an identical dwelling rates SAP 87 with "Connected to
+    # Dwelling = Yes" (credit -£167) vs SAP 74 with "No" (credit £0).
+    array = [make_pv_array(peak_power=3.0)]
+
+    def _gen(pv_connection: int) -> float:
+        epc = make_minimal_sap10_epc(
+            dwelling_type="Mid-terrace house",
+            total_floor_area_m2=70.0,
+            habitable_rooms_count=3,
+            country_code="ENG",
+            photovoltaic_arrays=array,
+            is_dwelling_export_capable=True,
+            pv_connection=pv_connection,
+        )
+        return cert_to_inputs(epc).pv_generation_kwh_per_yr
+
+    # pv_connection=2 (connected to the dwelling's meter) → PV serves the
+    # dwelling and is credited.
+    assert _gen(2) > 0.0
+    # pv_connection=1 (present but NOT connected to the dwelling's meter) →
+    # the array contributes nothing to this dwelling's SAP.
+    assert _gen(1) == 0.0