diff --git a/applications/modelling_e2e/handler.py b/applications/modelling_e2e/handler.py
index cf1d1564..da47719d 100644
--- a/applications/modelling_e2e/handler.py
+++ b/applications/modelling_e2e/handler.py
@@ -284,6 +284,21 @@ def _spatial_for(
         return None
 
 
+# The 32-wide fallback gap between this container's Solar calls: 0.8 (safety
+# headroom) × 600 QPM ÷ 60 ÷ 32 containers ≈ one call every 4s. Used when the
+# env var is unset so the Lambda self-protects even if terraform wiring is missed.
+_DEFAULT_SOLAR_MIN_REQUEST_INTERVAL_SECONDS: float = 4.0
+
+
+def _solar_min_request_interval_seconds() -> float:
+    """Per-container minimum gap (seconds) between Google Solar API calls, read
+    from ``SOLAR_MIN_REQUEST_INTERVAL_SECONDS``. Terraform derives the value from
+    the queue's ``maximum_concurrency`` (0.8 × 10 QPS ÷ N) so the up-to-32-wide
+    fleet stays under the hard 600 QPM Solar ceiling. Falls back to the 32-wide
+    default when unset or unparseable."""
+    raise NotImplementedError
+
+
 def _solar_insights_for(
     solar_client: GoogleSolarApiClient, spatial: Optional[SpatialReference]
 ) -> Optional[dict[str, Any]]:
diff --git a/tests/applications/modelling_e2e/test_handler.py b/tests/applications/modelling_e2e/test_handler.py
index 860e5313..7f11c7d7 100644
--- a/tests/applications/modelling_e2e/test_handler.py
+++ b/tests/applications/modelling_e2e/test_handler.py
@@ -123,6 +123,43 @@ def _baseline_orchestrator() -> Iterator[MagicMock]:
         yield orchestrator
 
 
+# ---------------------------------------------------------------------------
+# Solar throttle: per-container call gap resolved from env (quota/N safety)
+# ---------------------------------------------------------------------------
+
+
+def test_solar_min_request_interval_falls_back_to_32_wide_default() -> None:
+    # Arrange — env var absent: the Lambda must still self-protect at the 32-wide
+    # gap so a missed terraform wiring can't reopen the 600 QPM over-quota storm.
+    from applications.modelling_e2e.handler import (
+        _DEFAULT_SOLAR_MIN_REQUEST_INTERVAL_SECONDS,
+        _solar_min_request_interval_seconds,
+    )
+
+    with patch.dict("os.environ", {}, clear=True):
+        # Act
+        result = _solar_min_request_interval_seconds()
+
+    # Assert
+    assert result == _DEFAULT_SOLAR_MIN_REQUEST_INTERVAL_SECONDS
+
+
+def test_solar_min_request_interval_reads_env_when_set() -> None:
+    # Arrange — terraform injects the computed gap (e.g. a smaller N → smaller gap).
+    from applications.modelling_e2e.handler import (
+        _solar_min_request_interval_seconds,
+    )
+
+    with patch.dict(
+        "os.environ", {"SOLAR_MIN_REQUEST_INTERVAL_SECONDS": "2.0"}, clear=True
+    ):
+        # Act
+        result = _solar_min_request_interval_seconds()
+
+    # Assert
+    assert result == 2.0
+
+
 # ---------------------------------------------------------------------------
 # Trigger body validation
 # ---------------------------------------------------------------------------