Spectral Solar Radiation Data Base Documentation, Vol. I

Volume I

Table of Contents



Figure 2-1 Spectral and broadband solar radiation collection at FSEC, Cape Canaveral, Fla., in conjunction with photovoltaic module data in the same plane

Figure 2-2 Data collection site at PG&E, San Ramon, Calif.

Figure 2-3 Data collection site at Welby, Colo., where SERI acquired research data to study air pollution effects on solar radiation

Figure 3-1 The atmosphere acts as a temporally and spatially variable filter on solar radiation. The path length (air mass) of direct-beam radiation increases with increasing solar zenith angle; scattering and absorption increase with longer path lengths. Global radiation on a horizontal plane (Gh) is equal to the direct-beam radiation (from the solar disk) normal to the surface (Dn), multiplied by the cosine of the solar zenith angle (z), plus scattered radiation from the sky (S). For a tilted (rather than horizontal) plane, Dn is multiplied by the cosine of the incidence angle. The surface also receives radiation reflected from the ground to the surface (R).

These relationships are:

  Direct normal		Dn
  Global horizontal	Gh = Dn x Cos(z) + S
  Global normal		Gn = Dn + S + R
  Global tilt		Gt = Dn x Cos() + S + R


Figure 3-2 Spectroradiometers equipped with view-limiting tubes to acquire direct-normal solar radiation. Aluminum foil was placed over the instruments to reflect radiation and keep the instruments from overheating

Figure 3-3 Spectroradiometers equipped with integrating spheres to measure global solar radiation

Figure 3-4 Spectroradiometers equipped with the Teflon dome receivers

Figure 3-5 Outdoor intercomparison of four spectroradiometers

Figure 3-6 Examples of the very few distorted spectra in the data base (a,b,c). Broadband solar radiation data (d), corresponding with the spectra in b and c, show that irradiance was decreasing at 10:31 due to partly cloudy conditions

Figure 3-7 Example of all-sky photographs acquired at FSEC. These photographs provided evidence of rain, possible condensation on optics, and clouds

Figure 3-8 Example of all-sky photograph acquired at SERI with a disk blocking sun to show diffuse sky conditions

Figure 3-9 Example of the instrument configuration data recorded with the measured data

Figure 3-10 Example of the computer terminal output during a quality-control session

Figure 4-1 Examples of (a) direct-normal and (b) global-normal spectra and (c) broadband solar radiation measured at FSEC on a clear day

Figure 4-2 Examples of (a) direct-normal and (b) global-tilt spectra and (c) broadband solar radiation measured at FSEC on a cloudy day

Figure 4-3 Examples of global-normal spectra (upper) and broadband solar radiation (lower) measured at FSEC on a partly cloudy day. The spectrum at 16:31 shows data dropout during data transfer

Figure 4-4 Examples of solar spectra enhanced by cloud bright spots (a) at 10:31 on day 132 and (c) at 12:30 on day 133, and corresponding [(b) and (d), respectively] broadband solar radiation

Figure 4-5 Examples of direct-normal, global-horizontal, and diffuse-horizontal spectra measured by SERI on two days

Figure 4-6.a
Figure 4-6.b
Figure 4-6.c
Figure 4-6.d
Figure 4-6.e
Figure 4-6.f
The cumulative number of spectra (horizontal axis) measured over a range of air mass and atmospheric descriptors (vertical axis)

Figure 4-7 Examples of spectra showing noisy data in the ultraviolet (300- 400 nm) and near-infrared (1000-1100 nm) regions

Figure 5-1 Estimated total spectral measurement uncertainty for global measurements with the integrating spheres on (a) units number 102, 158, and 174; (b) global-normal measurements with the Teflon dome receivers on units 174 and 218; and (c) direct-normal measurements with the view-limiting tubes on units 158, 172, and 174. The measurement uncertainty is symmetrical except in (a) where a -8% bias is included in the lower limit for global-horizontal and global-tilt cases due to nonuniform sphere response when a strong direct-beam component is present

Figure 5-2 Comparison of the spectral intensity of an outdoor global- normal measurement and the NIST calibration lamp source. Low lamp values below 400 nm result in high measurement uncertainty

Figure 5-3 Between-instrument precision for global-normal spectral solar radiation measurements using the integrating spheres

Figure 5-4 Ratio of the spectroradiometer detector response at different temperatures to the response at 40° C

Figure 6-1 Example of the instrument configuration data on the data base tape. The numbers refer to:

  1. "C" indicating configuration
  2. FSEC 1987 Day 122 at 8:13 standard time
  3. Latitude
  4. Longitude
  5. Elevation
  6. Reference to configuration file that will be found in the data files
  7. Starting data-acquisition time plus number of attempts to acquire spectra (which would extend the data acquisition time)
  8. Number of data channels
  9. Number of spectra (0 for configuration files; 1 or 2 for data files)
  10. Number of lines in this segment

Figure 6-2 Examples of the data on the data-base tape

Figure 6-3 Example of quality-control information on the data-base tape

Figure 6-4 Examples of daily notes on the data-base tape

Figure 6-5 Examples of spectral measurement uncertainty on the data- base tape. A value of 100 indicates greater than 100% measurement uncertainty

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