diff --git a/custom_components/solar_optimizer/const.py b/custom_components/solar_optimizer/const.py
index e064dee..6d38a06 100644
--- a/custom_components/solar_optimizer/const.py
+++ b/custom_components/solar_optimizer/const.py
@@ -38,6 +38,17 @@ def name_to_unique_id(name: str) -> str:
     return slugify(name).replace("-", "_")
 
 
+def seconds_to_hms(seconds):
+    """Convert seconds to a formatted string of hours:minutes:seconds."""
+    hours = seconds // 3600
+    minutes = (seconds % 3600) // 60
+    secs = seconds % 60
+    if hours > 0:
+        return f"{hours}:{minutes:02d}:{secs:02d}"
+    else:
+        return f"{minutes}:{secs:02d}"
+
+
 class ConfigurationError(Exception):
     """An error in configuration"""
 
diff --git a/custom_components/solar_optimizer/sensor.py b/custom_components/solar_optimizer/sensor.py
index de6b197..8775f78 100644
--- a/custom_components/solar_optimizer/sensor.py
+++ b/custom_components/solar_optimizer/sensor.py
@@ -36,6 +36,7 @@
     get_tz,
     name_to_unique_id,
     DEVICE_MODEL,
+    seconds_to_hms,
 )
 from .coordinator import SolarOptimizerCoordinator
 
@@ -155,6 +156,8 @@ class TodayOnTimeSensor(SensorEntity, RestoreEntity):
                 {
                     "max_on_time_per_day_sec",
                     "max_on_time_per_day_min",
+                    "max_on_time_hms",
+                    "on_time_hms",
                 }
             )
         )
@@ -293,6 +296,8 @@ def update_custom_attributes(self):
             "last_datetime_on": self._last_datetime_on,
             "max_on_time_per_day_min": round(self._device.max_on_time_per_day_sec / 60),
             "max_on_time_per_day_sec": self._device.max_on_time_per_day_sec,
+            "on_time_hms": seconds_to_hms(self._attr_native_value),
+            "max_on_time_hms": seconds_to_hms(self._device.max_on_time_per_day_sec),
         }
 
     @property