feat(sigenergy): model the grid export limit from the plant's backfeed limit

apps/predbat/sigenergy.py

@@ -1768,6 +1768,15 @@ def _get_inverter_max_power_kw(self, system_id):
                 power += _safe_float(attr.get("ratedActivePower", 0))
         return power
 
+    def _get_export_limit_w(self, system_id):
+        """Return the grid export limit in W, or 99999 (no limit) when the system has not reported one.
+
+        The limit is the grid max backfeed power, which only arrives in an ``openapi/change`` MQTT
+        message (see _handle_mqtt_change). A reported 0 is skipped there, so it also reads as no limit.
+        """
+        backfeed_kw = _safe_float(self.systems.get(system_id, {}).get("gridMaxBackfeedPower", 0))
+        return round(backfeed_kw * 1000) if backfeed_kw > 0 else 99999
+
     # -----------------------------------------------------------------------
     # MQTT message handlers
     # -----------------------------------------------------------------------
@@ -2288,6 +2297,18 @@ async def publish_system_entities(self, system_id):
             app="sigenergy",
         )
 
+        # --- Export limit (W) ---
+        self.dashboard_item(
+            "sensor.{}_sigenergy_{}_export_limit".format(self.prefix, slug),
+            state=self._get_export_limit_w(system_id),
+            attributes={
+                "friendly_name": "Sigenergy {} Export Limit".format(system_name),
+                "unit_of_measurement": "W",
+                "device_class": "power",
+            },
+            app="sigenergy",
+        )
+
         # --- Operational mode (string) ---
         # flow_status (from MQTT) is preferred as it's the freshest, but fall back to the
         # REST-sourced current_mode (fetch_current_mode) so this doesn't read "Unknown" before
@@ -2380,6 +2401,7 @@ async def automatic_config(self):
         self.set_arg("battery_power", ["sensor.{}_sigenergy_{}_battery_power".format(self.prefix, s) for s in slugs])
         self.set_arg("battery_rate_max", ["sensor.{}_sigenergy_{}_battery_rate_max".format(self.prefix, s) for s in slugs])
         self.set_arg("inverter_limit", ["sensor.{}_sigenergy_{}_inverter_limit".format(self.prefix, s) for s in slugs])
+        self.set_arg("export_limit", ["sensor.{}_sigenergy_{}_export_limit".format(self.prefix, s) for s in slugs])
         self.set_arg("pv_power", ["sensor.{}_sigenergy_{}_pv_power".format(self.prefix, s) for s in slugs])
         self.set_arg("grid_power", ["sensor.{}_sigenergy_{}_grid_power".format(self.prefix, s) for s in slugs])
         self.set_arg("load_power", ["sensor.{}_sigenergy_{}_load_power".format(self.prefix, s) for s in slugs])

apps/predbat/tests/test_sigenergy.py

@@ -504,6 +504,47 @@ def test_sigenergy_automatic_config(my_predbat):
     assert api.set_args.get("load_today") == ["sensor.predbat_sigenergy_sig001_load_lifetime", "sensor.predbat_sigenergy_sig002_load_lifetime"], "load_today wired to lifetime totals"
     assert api.set_args.get("import_today") == ["sensor.predbat_sigenergy_sig001_grid_import_lifetime", "sensor.predbat_sigenergy_sig002_grid_import_lifetime"], "import_today wired to lifetime totals"
     assert api.set_args.get("export_today") == ["sensor.predbat_sigenergy_sig001_grid_export_lifetime", "sensor.predbat_sigenergy_sig002_grid_export_lifetime"], "export_today wired to lifetime totals"
+    assert api.set_args.get("export_limit") == ["sensor.predbat_sigenergy_sig001_export_limit", "sensor.predbat_sigenergy_sig002_export_limit"], "export_limit wired to the grid backfeed limit sensors"
+
+    return failed
+
+
+def test_sigenergy_publish_export_limit(my_predbat):
+    """The grid backfeed limit from an MQTT change message is published as the export limit sensor in W."""
+    failed = False
+    api = MockSigenergyAPI()
+
+    system_id = "SIG12345"
+    slug = api._system_slug(system_id)
+    api.systems[system_id] = {"systemName": "My Site"}
+    api.devices[system_id] = [{"deviceType": "Inverter", "attrMap": {"ratedActivePower": 12.0}}]
+
+    api._handle_mqtt_change(system_id, {"inverterMaxActivePowerW": "12000.0", "gridMaxBackfeedPowerW": "5000.0"})
+    run_async(api.publish_system_entities(system_id))
+
+    key = "sensor.predbat_sigenergy_{}_export_limit".format(slug)
+    assert key in api.dashboard_items, "Export limit entity published"
+    assert api.dashboard_items[key]["state"] == 5000, "Backfeed limit 5kW published as 5000W, got {}".format(api.dashboard_items[key]["state"])
+    assert api.dashboard_items[key]["attributes"].get("unit_of_measurement") == "W", "Export limit is in W so get_arg(required_unit='W') accepts it"
+
+    return failed
+
+
+def test_sigenergy_publish_export_limit_unknown(my_predbat):
+    """With no backfeed limit reported yet the export limit sensor reads 99999 W, i.e. no limit beyond the inverter's own."""
+    failed = False
+    api = MockSigenergyAPI()
+
+    system_id = "SIG12345"
+    slug = api._system_slug(system_id)
+    api.systems[system_id] = {"systemName": "My Site"}
+    api.devices[system_id] = [{"deviceType": "Inverter", "attrMap": {"ratedActivePower": 12.0}}]
+
+    run_async(api.publish_system_entities(system_id))
+
+    key = "sensor.predbat_sigenergy_{}_export_limit".format(slug)
+    assert key in api.dashboard_items, "Export limit entity published"
+    assert api.dashboard_items[key]["state"] == 99999, "Unknown backfeed limit published as 99999W, got {}".format(api.dashboard_items[key]["state"])
 
     return failed
 
@@ -4294,6 +4335,8 @@ def run_sigenergy_tests(my_predbat):
         ("publish_system_entities_operational_mode_fallback", test_sigenergy_publish_system_entities_operational_mode_fallback),
         ("publish_system_entities_operational_mode_invalid_value", test_sigenergy_publish_system_entities_operational_mode_invalid_value),
         ("automatic_config", test_sigenergy_automatic_config),
+        ("publish_export_limit", test_sigenergy_publish_export_limit),
+        ("publish_export_limit_unknown", test_sigenergy_publish_export_limit_unknown),
         ("fetch_controls", test_sigenergy_fetch_controls),
         ("publish_controls", test_sigenergy_publish_controls),
         ("parse_entity_system", test_sigenergy_parse_entity_system),

docs/components.md

@@ -1360,6 +1360,7 @@ Supports real-time monitoring (SOC, power flows, operational mode) and full char
 - The Sigenergy Developer Portal application must have **VPP Mode** enabled or charge/discharge commands will be rejected
 - On first startup Sigenergy sends an **onboarding approval email** — you must click the approval link before live MQTT data starts flowing
 - MQTT certificates (CA, client cert, client key) are required for TLS-authenticated connections to the broker
+- With `automatic: true` Predbat models your grid export limit (the plant's grid max backfeed power) from `sensor.predbat_sigenergy_<system>_export_limit`. Sigenergy only reports it when the plant's configuration changes, so until then the sensor reads 99999 W and exports are capped by the inverter limit alone
 
 #### Configuration Options (sigenergy)