diff --git a/etl/bill_savings/KwhData.py b/etl/bill_savings/KwhData.py
index 6b5f594a..24ce9f2c 100644
--- a/etl/bill_savings/KwhData.py
+++ b/etl/bill_savings/KwhData.py
@@ -259,6 +259,9 @@ class KwhData:
         # Create new features:
         data['estimate_annual_kwh'] = data['energy-consumption-current'] * data['total-floor-area']
 
+        # Ensure this is string, because we could have mixed types
+        data["lodgement-datetime"] = data["lodgement-datetime"].astype(str)
+
         if save:
             self.model_training_data_filepath = f"energy_consumption/{self.run_date}/training_data.parquet"
             logger.info(f"Storing energy consumption dataset in s3 at {self.consumption_data_filepath}")