Add function for accessing ERA5

docs/sphinx/source/reference/iotools.rst

@@ -237,6 +237,17 @@ lower quality.
    iotools.read_crn
 
 
+ECMWF ERA5
+^^^^^^^^^^
+
+A global reanalysis dataset providing weather and solar resource data.
+
+.. autosummary::
+   :toctree: generated/
+
+   iotools.get_era5
+
+
 Generic data file readers
 -------------------------
 

docs/sphinx/source/whatsnew/v0.13.2.rst

@@ -27,7 +27,8 @@ Enhancements
   :py:func:`~pvlib.singlediode.bishop88_mpp`,
   :py:func:`~pvlib.singlediode.bishop88_v_from_i`, and
   :py:func:`~pvlib.singlediode.bishop88_i_from_v`. (:issue:`2497`, :pull:`2498`)
-
+* Add :py:func:`~pvlib.iotools.get_era5`, a function for accessing
+  ERA5 reanalysis data. (:pull:`2573`)
 
 
 Documentation

pvlib/iotools/__init__.py

@@ -45,3 +45,4 @@
 from pvlib.iotools.meteonorm import get_meteonorm_observation_training  # noqa: F401, E501
 from pvlib.iotools.meteonorm import get_meteonorm_tmy  # noqa: F401
 from pvlib.iotools.nasa_power import get_nasa_power  # noqa: F401
+from pvlib.iotools.era5 import get_era5  # noqa: F401

pvlib/iotools/era5.py

@@ -0,0 +1,196 @@
+import requests
+import pandas as pd
+from io import BytesIO, StringIO
+import zipfile
+import time
+
+
+VARIABLE_MAP = {
+    # short names
+    'd2m': 'temp_dew',
+    't2m': 'temp_air',
+    'sp': 'pressure',
+    'ssrd': 'ghi',
+    'tp': 'precipitation',
+
+    # long names
+    '2m_dewpoint_temperature': 'temp_dew',
+    '2m_temperature': 'temp_air',
+    'surface_pressure': 'pressure',
+    'surface_solar_radiation_downwards': 'ghi',
+    'total_precipitation': 'precipitation',
+}
+
+
+def same(x):
+    return x
+
+
+def k_to_c(temp_k):
+    return temp_k - 273.15
+
+
+def j_to_w(j):
+    return j / 3600
+
+
+def m_to_cm(m):
+    return m / 100
+
+
+UNITS = {
+    'u100': same,
+    'v100': same,
+    'u10': same,
+    'v10': same,
+    'd2m': k_to_c,
+    't2m': k_to_c,
+    'msl': same,
+    'sst': k_to_c,
+    'skt': k_to_c,
+    'sp': same,
+    'ssrd': j_to_w,
+    'strd': j_to_w,
+    'tp': m_to_cm,
+}
+
+
+def get_era5(latitude, longitude, start, end, variables, api_key,
+             map_variables=True, timeout=60,
+             url='https://cds.climate.copernicus.eu/api/retrieve/v1/'):
+    """
+    Retrieve ERA5 reanalysis data from the ECMWF's Copernicus Data Store.
+
+    A CDS API key is needed to access this API.  Register for one at [1]_.
+
+    This API [2]_ provides a subset of the full ERA5 dataset.  See [3]_ for
+    the available variables.  Data are available on a 0.25° x 0.25° grid.
+
+    Parameters
+    ----------
+    latitude : float
+        In decimal degrees, north is positive (ISO 19115).
+    longitude: float
+        In decimal degrees, east is positive (ISO 19115).
+    start : datetime like or str
+        First day of the requested period.
+    end : datetime like or str
+        Last day of the requested period.
+    variables : list of str
+        List of variable names to retrieve.  See [1]_ for options.
+    api_key : str
+        ECMWF CDS API key.
+    map_variables : bool, default True
+        When true, renames columns of the DataFrame to pvlib variable names
+        where applicable. Also converts units of some variables. See variable
+        :const:`VARIABLE_MAP` and :const:`UNITS`.
+    timeout : int, default 60
+        Number of seconds to wait for the requested data to become available
+        before timeout.
+    url : str, optional
+        API endpoint URL.
+
+    Raises
+    ------
+    Exception
+        If ``timeout`` is reached without the job finishing.
+
+    Returns
+    -------
+    data : pd.DataFrame
+        Time series data. The index corresponds to the start of the interval.
+    meta : dict
+        Metadata.
+
+    References
+    ----------
+    .. [1] https://cds.climate.copernicus.eu/
+    .. [2] https://cds.climate.copernicus.eu/datasets/reanalysis-era5-single-levels-timeseries?tab=overview
+    .. [3] https://confluence.ecmwf.int/pages/viewpage.action?pageId=505390919
+    """  # noqa: E501
+    start = pd.to_datetime(start).strftime("%Y-%m-%d")
+    end = pd.to_datetime(end).strftime("%Y-%m-%d")
+
+    headers = {'PRIVATE-TOKEN': api_key}
+
+    # allow variables to be specified with pvlib names
+    reverse_map = {v: k for k, v in VARIABLE_MAP.items()}
+    variables = [reverse_map.get(k, k) for k in variables]
+
+    # Step 1: submit data request (add it to the queue)
+    params = {
+        "inputs": {
+            "variable": variables,
+            "location": {"longitude": longitude, "latitude": latitude},
+            "date": [f"{start}/{end}"],
+            "data_format": "csv"
+        }
+    }
+    slug = "processes/reanalysis-era5-single-levels-timeseries/execution"
+    response = requests.post(url + slug, json=params, headers=headers,
+                             timeout=timeout)
+    submission_response = response.json()
+    if not response.ok:
+        raise Exception(submission_response)  # likely need to accept license
+
+    job_id = submission_response['jobID']
+
+    # Step 2: poll until the data request is ready
+    slug = "jobs/" + job_id
+    poll_interval = 1
+    num_polls = 0
+    while True:
+        response = requests.get(url + slug, headers=headers, timeout=timeout)
+        poll_response = response.json()
+        job_status = poll_response['status']
+
+        if job_status == 'successful':
+            break  # ready to proceed to next step
+        elif job_status == 'failed':
+            msg = (
+                'Request failed. Please check the ECMWF website for details: '
+                'https://cds.climate.copernicus.eu/requests?tab=all'
+            )
+            raise Exception(msg)
+
+        num_polls += 1
+        if num_polls * poll_interval > timeout:
+            raise requests.exceptions.Timeout(
+                'Request timed out. Try increasing the timeout parameter or '
+                'reducing the request size.'
+            )
+
+        time.sleep(1)
+
+    # Step 3: get the download link for our requested dataset
+    slug = "jobs/" + job_id + "/results"
+    response = requests.get(url + slug, headers=headers, timeout=timeout)
+    results_response = response.json()
+    download_url = results_response['asset']['value']['href']
+
+    # Step 4: finally, download our dataset.  it's a zipfile of one CSV
+    response = requests.get(download_url, timeout=timeout)
+    zipbuffer = BytesIO(response.content)
+    archive = zipfile.ZipFile(zipbuffer)
+    filename = archive.filelist[0].filename
+    csvbuffer = StringIO(archive.read(filename).decode('utf-8'))
+    df = pd.read_csv(csvbuffer)
+
+    # and parse into the usual formats
+    metadata = submission_response['metadata']  # include messages from ECMWF
+    metadata['jobID'] = job_id
+    if not df.empty:
+        metadata['latitude'] = df['latitude'].values[0]
+        metadata['longitude'] = df['longitude'].values[0]
+
+    df.index = pd.to_datetime(df['valid_time']).dt.tz_localize('UTC')
+    df = df.drop(columns=['valid_time', 'latitude', 'longitude'])
+
+    if map_variables:
+        # convert units and rename
+        for shortname in df.columns:
+            converter = UNITS.get(shortname, same)
+            df[shortname] = converter(df[shortname])
+        df = df.rename(columns=VARIABLE_MAP)
+
+    return df, metadata

tests/conftest.py

@@ -130,6 +130,19 @@ def nrel_api_key():
     reason='requires solaranywhere credentials')
 
 
+try:
+    # Attempt to load ECMWF API key used for testing
+    # pvlib.iotools.get_era5
+    ecwmf_api_key = os.environ["ECMWF_API_KEY"]
+    has_ecmwf_credentials = True
+except KeyError:
+    has_ecmwf_credentials = False
+
+requires_ecmwf_credentials = pytest.mark.skipif(
+    not has_ecmwf_credentials,
+    reason='requires ECMWF credentials')
+
+
 try:
     import statsmodels  # noqa: F401
     has_statsmodels = True

tests/iotools/test_era5.py

@@ -0,0 +1,81 @@
+"""
+tests for pvlib/iotools/era5.py
+"""
+
+import pandas as pd
+import pytest
+import pvlib
+import requests
+import os
+from tests.conftest import RERUNS, RERUNS_DELAY, requires_ecmwf_credentials
+
+
+@pytest.fixture
+def params():
+    api_key = os.environ["ECMWF_API_KEY"]
+
+    return {
+        'latitude': 40.01, 'longitude': -80.01,
+        'start': '2020-06-01', 'end': '2020-06-01',
+        'variables': ['ghi', 'temp_air'],
+        'api_key': api_key,
+    }
+
+
+@pytest.fixture
+def expected():
+    index = pd.date_range("2020-06-01 00:00", "2020-06-01 23:59", freq="h",
+                          tz="UTC")
+    index.name = 'valid_time'
+    temp_air = [16.6, 15.2, 13.5, 11.2, 10.8, 9.1, 7.3, 6.8, 7.6, 7.4, 8.5,
+                8.1, 9.8, 11.5, 14.1, 17.4, 18.3, 20., 20.7, 20.9, 21.5,
+                21.6, 21., 20.7]
+    ghi = [153., 18.4, 0., 0., 0., 0., 0., 0., 0., 0., 0., 60., 229.5,
+           427.8, 620.1, 785.5, 910.1, 984.2, 1005.9, 962.4, 844.1, 685.2,
+           526.9, 331.4]
+    df = pd.DataFrame({'temp_air': temp_air, 'ghi': ghi}, index=index)
+    return df
+
+
+@requires_ecmwf_credentials
+@pytest.mark.remote_data
+@pytest.mark.flaky(reruns=RERUNS, reruns_delay=RERUNS_DELAY)
+def test_get_era5(params, expected):
+    df, meta = pvlib.iotools.get_era5(**params)
+    pd.testing.assert_frame_equal(df, expected, check_freq=False, atol=0.1)
+    assert meta['longitude'] == -80.0
+    assert meta['latitude'] == 40.0
+    assert isinstance(meta['jobID'], str)
+
+
+@requires_ecmwf_credentials
+@pytest.mark.remote_data
+@pytest.mark.flaky(reruns=RERUNS, reruns_delay=RERUNS_DELAY)
+def test_get_era5_map_variables(params, expected):
+    df, meta = pvlib.iotools.get_era5(**params, map_variables=False)
+    expected = expected.rename(columns={'temp_air': 't2m', 'ghi': 'ssrd'})
+    df['t2m'] -= 273.15  # apply unit conversions manually
+    df['ssrd'] /= 3600
+    pd.testing.assert_frame_equal(df, expected, check_freq=False, atol=0.1)
+    assert meta['longitude'] == -80.0
+    assert meta['latitude'] == 40.0
+    assert isinstance(meta['jobID'], str)
+
+
+@requires_ecmwf_credentials
+@pytest.mark.remote_data
+@pytest.mark.flaky(reruns=RERUNS, reruns_delay=RERUNS_DELAY)
+def test_get_era5_error(params):
+    params['variables'] = ['nonexistent']
+    match = 'Request failed. Please check the ECMWF website'
+    with pytest.raises(Exception, match=match):
+        df, meta = pvlib.iotools.get_era5(**params)
+
+
+@requires_ecmwf_credentials
+@pytest.mark.remote_data
+@pytest.mark.flaky(reruns=RERUNS, reruns_delay=RERUNS_DELAY)
+def test_get_era5_timeout(params):
+    match = 'Request timed out. Try increasing'
+    with pytest.raises(requests.exceptions.Timeout, match=match):
+        df, meta = pvlib.iotools.get_era5(**params, timeout=1)