diff --git a/pvnet_app/data/satellite.py b/pvnet_app/data/satellite.py
index 8c77d30..2c8c0cf 100644
--- a/pvnet_app/data/satellite.py
+++ b/pvnet_app/data/satellite.py
@@ -2,6 +2,7 @@
 import pandas as pd
 import xarray as xr
 import logging
+from typing import Optional
 import os
 import fsspec
 import ocf_blosc2
@@ -214,7 +215,7 @@ def interpolate_missing_satellite_timestamps(max_gap: pd.Timedelta) -> None:
         ds_sat.to_zarr(sat_path)
 
     
-def extend_satellite_data_with_nans(t0: pd.Timestamp) -> None:
+def extend_satellite_data_with_nans(t0: pd.Timestamp, satellite_data_path: Optional[str] = sat_path) -> None:
     """Fill the satellite data with NaNs out to time t0
     
     Args:
@@ -222,7 +223,7 @@ def extend_satellite_data_with_nans(t0: pd.Timestamp) -> None:
     """
 
     # Find how delayed the satellite data is
-    ds_sat = xr.open_zarr(sat_path)
+    ds_sat = xr.open_zarr(satellite_data_path)
     sat_max_time = pd.to_datetime(ds_sat.time).max()
     delay = t0 - sat_max_time
 
@@ -244,8 +245,8 @@ def extend_satellite_data_with_nans(t0: pd.Timestamp) -> None:
         ds_sat = ds_sat.reindex(time=np.concatenate([ds_sat.time, fill_times]), fill_value=np.nan)
 
         # Re-save inplace
-        os.system(f"rm -rf {sat_path}")
-        ds_sat.to_zarr(sat_path)
+        os.system(f"rm -rf {satellite_data_path}")
+        ds_sat.to_zarr(satellite_data_path)
 
 
 def check_model_satellite_inputs_available(
diff --git a/tests/data/test_satellite.py b/tests/data/test_satellite.py
index 5a367bc..b43c753 100644
--- a/tests/data/test_satellite.py
+++ b/tests/data/test_satellite.py
@@ -26,6 +26,7 @@
     sat_path,
     sat_5_path,
     sat_15_path,
+    extend_satellite_data_with_nans
 )
 
 
@@ -183,7 +184,6 @@ def test_preprocess_old_sat_5_data(sat_5_data_delayed, sat_15_data, test_t0):
         check_timesteps(sat_path, expected_freq_mins=5)
 
 
-
 def test_check_model_satellite_inputs_available(config_filename):
 
     t0 = datetime(2023,1,1)
@@ -194,3 +194,46 @@ def test_check_model_satellite_inputs_available(config_filename):
     assert check_model_satellite_inputs_available(config_filename, t0, sat_datetime_1)
     assert check_model_satellite_inputs_available(config_filename, t0, sat_datetime_2)
     assert not check_model_satellite_inputs_available(config_filename, t0, sat_datetime_3)
+
+
+def test_extend_satellite_data_with_nans(sat_5_data, test_t0):
+
+    # make temporary directory
+    with tempfile.TemporaryDirectory() as tmpdirname:
+
+        # Change to temporary working directory
+        os.chdir(tmpdirname)
+
+        # save sat to zarr
+        filename = "sat_5_data.zarr"
+        sat_5_data.to_zarr(filename)
+
+        time = sat_5_data.time.values
+        t0 = pd.to_datetime(sat_5_data.time).max()
+        extend_satellite_data_with_nans(t0=t0, satellite_data_path=filename)
+
+        # load new file
+        ds = xr.open_zarr(filename)
+        assert (ds.time.values == time).all()
+
+
+def test_extend_satellite_data_with_nans_over_3_hours(sat_5_data, test_t0):
+
+    # make temporary directory
+    with tempfile.TemporaryDirectory() as tmpdirname:
+
+        # Change to temporary working directory
+        os.chdir(tmpdirname)
+
+        # save sat to zarr
+        filename = "sat_5_data.zarr"
+        sat_5_data.to_zarr(filename)
+
+        time = sat_5_data.time.values
+        t0 = pd.to_datetime(sat_5_data.time).max() + pd.Timedelta(hours=4)
+        extend_satellite_data_with_nans(t0=t0, satellite_data_path=filename)
+
+        # load new file
+        ds = xr.open_zarr(filename)
+        assert len(time) + 3*12 == len(ds.time)
+        assert ds.time.values[-1] == t0