Interpreting Cylinder Plots
SERI_QC Flags:
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DQMS assigns a 2-digit data quality flag to each 1-minute data value for global (broadband hemispheric downwelling shortwave), direct normal, and diffuse horizontal irradiance components. This graphical portion of the report shows the worst offending flag value (worst flag from among all irradiance components at that point) as a gray-scale; white to light-gray is good data quality; dark gray to black is poor or missing data quality.
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DQMS converts the 1-minute irradiance data from units of Watts per square meter to fractional values based on the corresponding extraterrestrial value for the time and site location of the measurement. High irradiance levels translate to lighter shades and low irradiance levels are darker shades (black is night-time or heavy overcast when the pyrheliometer measures at or near zero irradiance).
| Irradiance Element | Symbol | K-Space Conversion |
|---|---|---|
| Global Horizontal | Kt | Global / Isc * ECF * Cos(Z) |
| Direct Normal | Kn | Direct / Isc * ECF |
| Diffuse Horizontal | Kd | Diffuse / Isc * ECF * Cos(Z) |
ECF = Eccentricity Correction Factor = (ro / r)2
r = current Earth-Sun distance |
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Data availability and data quality statistics are available for each irradiance component. Statistics are available for four levels of interest:
- High-quality (data judged to be within 5% of true values)
- Questionable data quality (greater than 10% uncertainties)
- Above or below empirical limits (time of day dependent; e.g., -1.23 for DHI is below empirical limits at 12:00 PM, or nighttime irradiances less than -10 Wm-2)
- Data seem outside quality limits, but collectively agree with internal constraints (global = direct normal * Cos(Z) + diffuse).
[NREL] [MIDC]