diff --git a/src/batcontrol/forecastsolar/solarprognose.py b/src/batcontrol/forecastsolar/solarprognose.py
index 0f8ee4f8..3ece7648 100644
--- a/src/batcontrol/forecastsolar/solarprognose.py
+++ b/src/batcontrol/forecastsolar/solarprognose.py
@@ -62,8 +62,11 @@ def __init__(self, pvinstallations, timezone, min_time_between_api_calls,
             delay_evaluation_by_seconds: Delay for API evaluation
             target_resolution: Target resolution in minutes (15 or 60)
         """
+        # Provider allows 20 calls/day; use 18 to leave 2 in reserve (~80 min).
+        # Integer arithmetic avoids float rounding; max() respects larger caller values.
+        _provider_min = 24 * 60 * 60 // 18  # 4800 s
         super().__init__(pvinstallations, timezone,
-                         min_time_between_api_calls, delay_evaluation_by_seconds,
+                         max(min_time_between_api_calls, _provider_min), delay_evaluation_by_seconds,
                          target_resolution=target_resolution,
                          native_resolution=60)  # SolarPrognose provides hourly data