10 measuring the spectral and angular distribution of the diffuse solar radiance
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The document discusses the measurement of the spectral and angular distribution of diffuse solar radiance, emphasizing the need for accurate angle of incidence correction based on isotropic assumptions. It details the measurement equipment used, including various spectrometers and their specifications, as well as the procedures for calibration and data analysis. The findings highlight the angular distribution of sky radiance under different conditions, with suggestions for future tasks to enhance measurement accuracy and reliability.
10 measuring the spectral and angular distribution of the diffuse solar radiance
- 1. Measuring the spectral and angular distribution of the diffuse solar radiance Stefan Riechelmann, Thomas Fey, Dirk Friedrich, Stefan Winter Department 4.1: Photometry and Applied Radiometry Working Group 4.14: Solar Cells
- 2. Why do we need the angular distribution? 2 Stefan Riechelmann 61853-3 (Draft): Angle of incidence correction of diffuse irradiance is proposed after (Martin and Ruiz 2001): Assumption of an isotropic distribution of diffuse irradiance 𝐷p,corr = λ Ω 𝑠 Ω, λ ⋅ (𝐷p,sky(Ω, λ) + 𝐷p,ground(Ω, λ)) ⅆΩ ⅆλ If we measure the spectral and angular distribution of a real radiance field, we can evaluate the uncertainty arising from assumptions made in the energy rating. 𝐷p,ground 𝐷 𝑝,𝑠𝑘𝑦 𝐵𝑝
- 3. Measurement equipment - spectrometer 3 Stefan Riechelmann UV+VIS Spektrometer (CAS 140CT – 154) Wavelength range: 220 - 1020 nm Bandwidth : 3,7 nm Sampling interval : 0,8 nm Infrared Spektrometer (CAS 140CT – 171) Wavelength range: 780 - 1650 nm Bandwidth: 9 nm Sampling interval: 3 nm Extended IR Spectrometer (CAS 140CT – 175) Wavelength range: 1500 - 2150 nm Bandwidth: 15 nm Sampling interval: 4 nm Entrance Optics Field of View: 5° FWHM Stray light reduced design Digital Camera Field of View: 120° For quality control and documentation purposes Dual Axis Tracking Unit Range zenith: -42.5° - 105° Range azimuth: -10° - 370°
- 4. Measurement equipment – entrance optics 4 Stefan Riechelmann 5,9 mm 9,8 mm >17,7 mm 1° 2,5° 112,35 mm 168,53 mm ISO 9060/World Meteorological Organisation (WMO) Recommendations (Analog PM06 and Pyrheliometer) • Field of view (full angle): 5° • Slope Angle: 1° 10-6 10-4 10 -2 100 -20 20 600 40 80 with extension and spectral black foil and soot norm.signal/a.u. Radiance entrance optics: Field of View of 5° FWHM Reduced stray light effects by using black foil for the interior and soot for the baffles. Stray light at incidence angles > 10° is lower than 10-6.
- 5. Measurement equipment – radiance calibration 5 Stefan Riechelmann spectral irradiance transfer standard baffle reflection standard entrance optics Radiance emitted by reflection standard: 𝐿lamp,λ = 𝑅(0°, 45°, 𝜆) 𝜋 ⋅ Elamp,λ Responsivity of the instrument: r 𝜆 = 𝑋lab 𝜆 𝐿lamp,λ 𝑐𝑜𝑢𝑛𝑡𝑠 W m−2nm−1sr−1 Calibrated outdoor measurement: Lsky,λ = 𝑋sky 𝜆 𝑟 𝜆 W m−2 nm−1 sr−1
- 6. 6 Sky radiance measurement at 20.07.2016, 14:34 MEZ (clear sky) control picture (North direction) Angular distribution at 400 nm Angular distribution at 1000 nm
- 7. 7 Angular distribution at 400 nm Sky radiance measurement at 20.07.2016, 14:34 MEZ (clear sky) control picture (North direction) Angular distribution at 1000 nm
- 8. Wavelength dependence of sky radiance 8 Stefan Riechelmann Angular distribution of radiance: • Black points: 145 measurements • Yellow points: solar position during scan • Green line: horizon at 85° zenith angle • Ground albedo has been calculated based on horizontal global irradiance Spectral Irradiance: • Direct irradiance measured at the beginning of the scan • Diffuse irradiance calculated by integral of the hemisphere
- 9. 9 Sky radiance measurement at 12.07.2016, 14:56 MEZ (broken clouds) control picture (North direction) Angular distribution at 400 nm Angular distribution at 1000 nm
- 10. 10 Angular distribution at 400 nm Sky radiance measurement at 12.07.2016, 14:56 MEZ (broken clouds) control picture (North direction) Angular distribution at 1000 nm
- 11. Follow-up tasks 11 - Comparison to integrating measurement instruments (i.e. solar cells, pyranometer) - Weatherproof housing for measurement equipment - Longer time series of measurements Especially necessary for performance evaluation under cloudy conditions - Comparison to isotropic / anisotropic models
- 12. Acknowledgements 12 This work was supported by the European Metrology Research Programme (EMRP) Project ENG55 PhotoClass, which is jointly funded by the EMRP participating countries within EURAMET and the European Union.