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State-of-the-Art Indoor Calibration for Pyranometers and Pyrheliometers

Explore indoor calibration methods, hierarchy of traceability, uncertainties, & industry requirements for enhanced solar energy assessments.

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State-of-the-Art Indoor Calibration for Pyranometers and Pyrheliometers

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  1. State of the art of indoor calibration of pyranometers and pyrheliometers

  2. Main points • Most field pyranometers are calibrated indoors • Many procedures for indoor calibration • Not all well connected to ISO 98-3 GUM • Industry requires straightforward approach

  3. Industry • Meteorology - Solar renewable energy • Site assessment • Installation performance • Professionalisation / IEC

  4. Conclusion • Points for discussion • Normal incidence calibration is preferred (diffuse dome not) • Uncertainty & accuracy of reference can be optimised • Pyrheliometer indoor calibration must be added

  5. Myself • Kees VAN DEN BOS • Engineer Physics • Director / owner Hukseflux Thermal Sensors • Last 20 years sensor design

  6. Hukseflux 2010

  7. Hukseflux international

  8. Founded 1993 Thermal sensors 15 employees 5 radiometry compensation pyrheliometer Hukseflux DR01 pyrheliometer

  9. Hukseflux solar concentrator sensors

  10. Background • Most pyranometers and pyrheliometers have indoor calibration • Exception: highest accuracy (BSRN, outdoor) • Exception: Japan, China (outdoor) • Cost, time, weather; outdoor calibration is unacceptable to industry

  11. Present status (excerpt) • Eppley, US Weather Bureau: indoor integrating diffuse source • Kipp, Hukseflux: indoor normal incidence • EKO, JMA: outdoor tracker with collimation tube (changes) • China: outdoor

  12. ISO 9060

  13. ISO 9060

  14. Background • Measurement uncertianty is a function of: • Characterisation / class • Calibration • Measurement & maintenance conditions • Environmental conditions

  15. Background • Indoor calibration covered by ISO 9847 • Present ASME: “Indoor Transfer of Calibration from Reference to Field Pyranometers”

  16. Indoor calibration

  17. ISO 9846

  18. ISO 9847 also indoor

  19. ISO 98-3 GUM

  20. Hierarchy of Traceability • A: Reference calibration (uncertainty) • B: Correction of reference to indoor conditions (uncertainty) • C: Indoor calibration of field instrument (uncertainty) • Indoor calibration uncertainty estimate (A+B+C) • Field measurement uncertainty estimate

  21. Hierarchy of Traceability • A: Reference calibration (uncertainty) • B: Correction of reference to indoor conditions (uncertainty) • C: Indoor calibration of field instrument (uncertainty) • Indoor calibration uncertainty estimate (A+B+C)

  22. ISO 98-3 GUM

  23. Hierarchy of traceability

  24. ISO 98-3 GUM

  25. Hierarchy of Traceability • KNMI TR 235 "uncertainty in pyranometer and pyrheliometer measurements at KNMI in De Bilt".

  26. ISO 98-3 GUM

  27. Hierarchy of Traceability • A: Reference calibration (uncertainty) (conditions and class) • B: Correction of reference to indoor conditions (uncertainty) • C: Indoor calibration of field instrument (uncertainty) • Indoor calibration uncertainty estimate (A+B+C) • Field measurement uncertainty estimate (conditions & class)

  28. Strange… • Errors in reference calibration re-appear in measurement errors • Counted double • At least systematic errors (Zero offset A and directional errors) can be avoided.

  29. One step back • Present approach works well if calibrated instruments are used: • Outdoor / unventilated • Without applying GUM analysis • At same latitude

  30. One step back • Present approach does not work well calibrated if instruments are used: • As indoor reference • Applying GUM analysis • At other latitudes • Ventilated

  31. Typical calibration • Irradiance 800 W/m2 • 40 to 60 degrees angle of incidence, + / - 30 degrees azimuth • Zero offset A: -9 +/- 3 W/m2 (larger than ISO9060) • Directional: +/- 10 W/m2 @ 1000 W/m2 , now estimated +/- 5 W/m2

  32. Typical calibration • PMOD specified uncertainty +/- 1.3% • Systematic error -1%? Type B.

  33. Improved approach • Zero offset A: -9 +/- 3 W/m2 (larger than ISO9060) • Directional: +/- 10 W/m2 • Solution 1: ventilation • Solution 2: single angle of incidence

  34. For consideration • Japanese collimated tube with tilt correction and ventilation

  35. Diffuse sphere source • Uniformity of sphere top-edge (experimental -13%) • Weighing for non uniform source requires weighing of reference with source • Diffuse sphere: weighing requires weiging of field instrument with source. Complicated! • Normal incidence: weighing of field instrument is not necessary

  36. Conclusion • Indoor calibration offers only acceptable solution for manufacturers and solar industry • “Normal incidence” calibration fits within ISO 98-3 GUM

  37. Conclusion • Indoor normal incidence calibration is preferred (diffuse dome not) • Accuracy and precision of reference can be optimised (single angle, ventilated) • Pyrheliometer indoor calibration must be added

  38. P.S. • Memo available via server

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