BSRN limits

The BSRN limit checks specify upper and lower limits for solar irradiance measurements, defining boundaries for GHI, DHI, and DNI as a function of the extraterrestrial irradiance.

The BSRN limits can be calculated using solarpy.quality.bsrn_limits(), and the corresponding quality flags can be calculated using solarpy.quality.bsrn_limits_flag().

There are two sets of limits for each component: the extremely rare limits (ERL), which are expected to be exceeded only in very rare cases, and the physically possible limits (PPL), which are not expected to be exceeded.

In the example below, GHI, DHI, and DNI measurements are plotted against the extraterrestrial irradiance on a horizontal plane using solarpy.plotting.plot_bsrn_limits(). The red shaded areas correspond to the ERL and PPL limits; the width of each band accounts for the variation of the Sun-Earth distance over the course of a year.

Load example data

The example data is from DTU’s station in Lyngby, Denmark north of Copenhagen. The data is from 2023 and includes measurements of GHI, DHI, and DNI at a 1-minute resolution.

import matplotlib.pyplot as plt
import numpy as np
import pvlib
import solarpy

data, meta = solarpy.iotools.read_t16(
    "https://raw.githubusercontent.com/AssessingSolar/solarpy/refs/heads/main/data/LYN_2023.csv",  # noqa: E501
    map_variables=True,
)

# Calculate solar position
solar_position = pvlib.solarposition.get_solarposition(
    data.index, latitude=meta["latitude"], longitude=meta["longitude"]
)

# Calculate extraterrestrial irradiance on a horizontal plane
dni_extra = pvlib.irradiance.get_extra_radiation(data.index)
cos_sza = np.cos(np.deg2rad(solar_position["apparent_zenith"])).clip(lower=0)
ghi_extra = dni_extra * cos_sza

Plot BSRN limits for GHI

The irradiance data is plotted against the extraterrestrial irradiance using a scatter heatmap to differentiate between high and low density areas.

The BSRN limits are plotted as red shaded areas. # Measurements falling outside the red bands are flagged as suspicious by solarpy.quality.bsrn_limits_flag() and should be inspected further.

fig, axes = solarpy.plotting.plot_bsrn_limits(
    irradiance=data["ghi"],
    component="ghi",
    ghi_extra=ghi_extra,
)

fig.tight_layout()

Plot BSRN limits for all three components

fig, axes = plt.subplots(ncols=3, figsize=(10, 5), sharey=True)

for ax, component in zip(axes, ["ghi", "dhi", "dni"]):
    solarpy.plotting.plot_bsrn_limits(
        irradiance=data[component],
        component=component,
        ghi_extra=ghi_extra,
        ax=ax,
    )

fig.tight_layout()

Estimated memory usage: 311 MB