Clearsky Limits for Daily Insolation

Checking the clearsky limits for daily insolation data.

Identifying and filtering out invalid irradiance data is a useful way to reduce noise during analysis. In this example, we use pvanalytics.quality.irradiance.daily_insolation_limits() to determine when the daily insolation lies between a minimum and a maximum value. Irradiance measurements and clear-sky irradiance on each day are integrated with the trapezoid rule to calculate daily insolation. For this example we will use data from the RMIS weather system located on the NREL campus in Colorado, USA.

import pvanalytics
from pvanalytics.quality.irradiance import daily_insolation_limits
import pvlib
import matplotlib.pyplot as plt
import pandas as pd
import pathlib

First, read in data from the RMIS NREL system. This data set contains 5-minute right-aligned data. It includes POA, GHI, DNI, DHI, and GNI measurements.

pvanalytics_dir = pathlib.Path(pvanalytics.__file__).parent
rmis_file = pvanalytics_dir / 'data' / 'irradiance_RMIS_NREL.csv'
data = pd.read_csv(rmis_file, index_col=0, parse_dates=True)
# Make the datetime index tz-aware.
data.index = data.index.tz_localize("Etc/GMT+7")

Now model clear-sky irradiance for the location and times of the measured data:

location = pvlib.location.Location(39.7407, -105.1686)
clearsky = location.get_clearsky(data.index)

Use pvanalytics.quality.irradiance.daily_insolation_limits() to identify if the daily insolation lies between a minimum and a maximum value. Here, we check GHI irradiance field ‘irradiance_ghi__7981’. pvanalytics.quality.irradiance.daily_insolation_limits() returns a mask that identifies data that falls between lower and upper limits. The defaults (used here) are upper bound of 125% of clear-sky daily insolation, and lower bound of 40% of clear-sky daily insolation.

daily_insolation_mask = daily_insolation_limits(data['irradiance_ghi__7981'],
                                                clearsky['ghi'])

Plot the ‘irradiance_ghi__7981’ data stream and its associated clearsky GHI data stream. Mask the GHI time series by its daily_insolation_mask.

data['irradiance_ghi__7981'].plot()
clearsky['ghi'].plot()
data.loc[daily_insolation_mask, 'irradiance_ghi__7981'].plot(ls='', marker='.')
plt.legend(labels=["RMIS GHI", "Clearsky GHI",
                   "Within Daily Insolation Limit"],
           loc="upper left")
plt.xlabel("Date")
plt.ylabel("GHI (W/m^2)")
plt.tight_layout()
plt.show()

previous

Irradiance-Quality

next

Clearsky Limits for Irradiance Data